8.1 Introduction

A range of marking techniques other than metal rings can be used to identify birds individually so they can be resighted without the need to catch them again, either for survival analyses, or to study movements and behaviour using data from devices attached to the individual. Well-designed projects with colour rings, colour marks, devices or using samples can provide valuable extra information on the lives of birds; however, the time needed to design and run a study should not be underestimated.

Whilst correctly fitted metal rings are thought to involve no or minimal risk to the bird carrying them, other marking techniques may present an increased risk to the bird, and could alter behaviour, breeding success or survival. Apart from the issue of bird welfare, such effects may invalidate the results of the study. The potential risks to the birds concerned, either from fitting or attaching the marks to the bird or from the mark itself, should therefore be considered carefully and weighed against the scientific benefits of the proposed study. Even simple colour rings may have a detrimental impact on some species; for example Hawfinch parents have been recorded removing colour-ringed chicks from the nest. Remote monitoring devices may  increase birds’ energetic costs as a result of the extra weight, aero or hydrodynamic drag and/or influence their behaviour or survival. Highly visible colour marks or devices may attract predators and also give rise to adverse comments from non-ringers. Careful design, taking into account colour, position and type of attachment or application, weight and season of application are important to reduce any potentially detrimental effects to acceptable levels. As a consequence, projects using Special Methods must be approved before they commence, and must be reviewed and permission renewed annually. This process is described in section 1.4.2 of Chapter 1 of the guidance, and referenced below in relation to the Special Methods Technical Panel.

Some of the less invasive sampling methods can also be licensed as Special Methods, as with certain conditions (agreed through discussion with the Home Office) they fall under the ASPA (Animals (Scientific Procedures) Act 1986) lower threshold (any procedure that causes a level of pain, suffering, distress, or lasting harm equivalent to, or higher than, that caused by inserting a hypodermic needle according to good veterinary practice is above the lower threshold). There are also several ‘non-conventional’ trapping methods that require Special Methods approval.

8.1.1 The roles of the Special Methods Technical Panel (SMTP) and BTO staff

Background

The Special Methods Technical Panel (SMTP) is a subcommittee of the Ringing Committee (RIN) and operates to agreed Terms of Reference.

BTO staff receive applications for new projects and for renewals and, depending on the type of project, may either approve the project, return it to the applicant with a request for more information, or refer it to SMTP. Whether or not a project needs to be assessed directly by SMTP depends on the overall level of risk the method poses, which varies between methods and between species, and is strongly influenced by how well established the method is for that particular species.

If a project is referred to SMTP, BTO staff will facilitate all communication between the applicant and SMTP. As with other RIN sub-committees, this is to ensure that members of the panel are not directly petitioned by applicants and that all discussion is visible to all members of the panel involved, and can be archived by staff to inform decisions about future applications.

Whilst much of the role of SMTP and BTO Licensing staff is focused on regulation of activities in order to ensure that all Special Methods projects comply with ASPA legislation, which both protects ringers and minimises the risk of reputational damage to the Ringing Scheme, we also aim to support ringers in their research, and to encourage collaboration between practitioners in order to improve methods and, ultimately, improve the welfare of birds.

Criteria for decision making

Applications are considered on a) the risk of harm to birds, b) whether the proposed technique will deliver the expected data and c) whether the data, if they are delivered, are of sufficient value to justify the risk, as set out in the SMTP Terms of Reference. This is assessed via the information provided in the application form; the level of detail required in the application form depends to some extent on the level of risk to birds represented by the method (see section 8.3 on Risk Assessments) as well as how well established the use of the method is on the species concerned. 

8.2 Making an application to use a Special Method (including colour rings)

8.2.1 What is a project?

A project relates to one species, and uses one attachment type, marking method, sampling method or trap. For projects fitting devices, multiple types of device can be used within a project, providing that it is clear in the annual report which type (e.g. make and model) of approved device has been applied to an individual. If multiple attachments or methods are to be used on the same individual, these need to be treated as separate projects, but the application should indicate that several methods will be applied to one individual. This is particularly important if multiple devices are to be fitted using different attachment methods, as the total weight of these devices will need to be taken into account when decisions are made regarding approval.

8.2.2 Who should be the project lead?

The project lead should be the person who is responsible for the practical implementation of the project, use of the method in the field, and for reporting on the project. They must be a C-, A- or S-permit holder with the relevant conventional endorsement(s) for the species in question, and sufficient experience of the method to be approved to use the method unsupervised. If the obvious choice to lead the project does not have sufficient experience, but is going to be trained by a practitioner with the relevant experience, the latter should be named as the lead initially, with the former being added as an agent once fully trained, and the project transferred to them at the next renewal. As an example, a student who is running a project as part of their PhD but is not sufficiently experienced to be approved as the lead could ask a ringer with the necessary experience to act as the project lead during the first season, training the student during that period. The student could then be added as an agent part way through that season, and then ask for the project to be transferred into their name at renewal.

8.2.3 Agents

Agents are permitted to carry out the method independently of the lead and therefore have to meet the same minimum standards of training and experience as the project lead before they can be added as an agent. To avoid Special Methods endorsements being added to permits where the skills have not yet been acquired, agents will not be added to a project before training has been completed. The application form allows you to indicate whether you consider the agents listed to be fully trained, in which case details of their experience will need to be provided, or if you are planning to train them in the initial stages of the project, in which case details of the planned training will need to be included in the application. When making your application, consider how many agents are needed. Whilst sometimes the complexities of fieldwork mean that it will be impossible to avoid adding agents speculatively, ideally, all of those listed should be an active part of the project. Adding additional agents can be done at short notice if needed during the fieldwork season, providing they already have sufficient training in, or previous experience of, the method. In order to add agents to a project, please complete the Adding or Removing Agent form.

Note that only ringers who need to use the method independently of the lead (or other agents) need to be added to the project; as with conventional methods, Special Methods can be carried out under the supervision of a suitably qualified ringer (i.e. someone with the appropriate endorsement and project permission). Anyone working under supervision should be added to the reporting form so that their experience working under the project is recorded. This will be useful should they wish to use the method independently at a later stage.

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8.3 Risk assessments/risk levels

The risk level of each method is determined by assessing the potential issues which could arise, the likelihood of each occurring, and the severity of any impact on the individual bird. This gives a risk level which influences several things:

• whether the method needs to be reviewed by SMTP, or if BTO licensing staff can approve the project using agreed protocols
• the type of training and experience that anyone using the method needs to have before they can operate independently
• which conditions are imposed on fieldwork
• what reporting is required

The following table provides a general summary for each method, based on the general risks involved. Most methods are not suitable for all species, and the risk level may be higher for some species due to their physiology, or simply due to the lack of evidence of safety.

Where a method is novel to the species, but safe on similar species, the method is likely to be allowed as a pilot study on a smaller number of birds, with more intensive monitoring and reporting requirements to mitigate any risk as much as possible. Details about which methods are likely to be approved on specific species groups can be found in the Approval Matrix section.

Table 8.1: Risk categorisation

8.3.1 How much training is needed?

Low risk - Although a demonstration of the technique from someone who has previously been approved to use the method is preferred, training can be achieved via written instructions or a video.

Medium risk - Requires one-to-one training from someone who has previously been approved to use the method with some practical field demonstrations (use of dead birds); except sampling which must include viewing of the BTO training videos (for buccal swabbing and feather pulling), submission of a video of the ringer performing the technique on a dead bird (for feather pulling), and followed up by the lead reviewing the ringer’s first live bird. (BTO staff perform this review function for the project lead).

High risk - Requires one-to-one training from a previously-licensed individual with some practical field demonstrations; supported with written instructions and/or a video.

Very high risk - In-person training from an individual who has previously used the method on that species (or from a very similar species, if the method is novel for the species). The ringer being trained will be expected to undertake the method on multiple individual birds under supervision. This should be preceded by other forms of training, such as demonstrating and practicing on a dead bird, or a captive bird. Written instructions and videos can also be helpful.

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8.4 Description of methods

8.4.1 Backpack tags

Backpack tags can be attached using harnesses, tape or glue, as described below. Their position offers several advantages: they are mounted close to the bird’s centre of lift, optimally exposed to sunlight for solar-powered devices, and well-placed for antenna orientation to communicate with satellites or other networks or receivers. Despite being the most effective position for solar charging, solar panels on backpacks remain vulnerable to shading from back feathers or closed wings. To try to mitigate the risk of solar shading, a tag is sometimes fitted with a soft foam pad that raises its height as well as making the base softer. 

The rule-of-thumb for backpacks (device and its attachments) is that they should weigh less than 3% of the bird's body weight. However, it may sometimes be acceptable for a proportionally heavier tag to be used for smaller species, especially for temporary attachments (e.g. glue or degradable harness). For large species 3% may be too heavy. 

Thoracic harnesses

There are several designs of 'thoracic', or 'full body' harnesses. In some, the straps converge at a single point on the sternum, while in others a breast strap runs along the sternum and is joined at each end by straps from the front and back of the tag. Harness materials, shape, and fitting techniques vary, and these differences can affect both safety and performance. Teflon ribbon is commonly used, but care must be taken to prevent twisting, which narrows the strap and increases the risk of abrasion. Teflon has no stretch, and in cases where a small degree of flexibility is desired, silicone tubing can be used. Low-tension elastic straps are rarely used and must be avoided for birds with long necks or bills, where they pose a risk of entanglement unless their stretch is very tightly limited. 

A tag fitted with a thoracic harness typically sits high on the bird's back. 

Leg-loop harnesses

These consist of two loops, one encircling the base of each leg. For larger species, Teflon ribbon is sometimes used, but more commonly the harness is made from a slightly elastic material such as silicone tubing. Low-tension elastic material should be avoided for large birds, as it increases the risk of entanglement. For smaller species, such as most passerines, the harness is typically made from 'beading elastic' (polyurethane). This material is suitable for long-term deployments (e.g. >1 year) because it degrades more slowly than rubber-based elastics, which are preferred for single-season deployments since the tag will detach from the bird sooner, when it breaks. 

A tag fitted with a leg-loop harness rests on the lower back, over the synsacrum. Care must be taken to ensure the tag does not interfere with the preen gland.

Weak Links

Some harness designs incorporate a weak link, intended to break and release the bird, ideally after the tag is no longer functioning (e.g. once its battery is depleted). While weak links are highly desirable from a welfare perspective, they also carry risks. It is difficult to predict precisely when a weak link will fail, particularly for tags that must remain attached for a year or longer. This creates the possibility of premature breakage, or conversely, of the link never breaking at all. When a weak link does fail, the harness must detach cleanly. Above all, harness fit and bird comfort remain the most important factors in ensuring safety, and the addition of a weak link must not compromise these.

Glue-mounting on the back (Adhesive Back)

Small tags can be glued to back feathers, usually with Superglue, but sometimes with epoxy resins or more flexible latex-based contact adhesives. On some tags the area for gluing is increased by adding a patch of thin, light material such as muslin cloth.

Tags can be fitted at any point on the back, and there are pros and cons of high and low locations. High on the back (the dorsal thorax) the tag is closer to the bird's centre of lift, but also at the highest/deepest point and therefore has greater effect on aerodynamic drag. Also, on some birds the shape of the upper back is somewhat 'roof-shaped', which doesn't match the flat underside of a tag. 

Lower down the back (the synsacrum) tends to be flatter, and a tag will have less impact on aerodynamics, but is further from the centre of lift. A solar-powered tag low on the back is more likely to be shaded by closed wing feathers. 

Glue-mounted tags will be shed at the next body feather moult, if not sooner, which is advantageous for bird welfare but unsuitable for long term remote tracking or where the tag must be recovered around a year after deployment to download data. 

Feathers may sometimes be trimmed before tags are attached and, particularly in these cases, tags may be deliberately or accidentally glued to skin as well as feathers. This can be problematic, especially if the glued area of skin is large or if the bird's skin is irritated by the glue. Most fast-curing glues are exothermic, which can exacerbate the problems. Generally, therefore, care should be taken not to glue to skin, or for the area to be small, with minimal quantity of glue. One potential exception is when fixing very small tags to downy chicks, and in these cases latex glues are preferred, including those specifically designed for gluing to human skin.

Tape-mounting on the back (Tape Back)

This method, mainly used for seabirds, uses single-sided adhesive tape to fix a tag to a small number (typically 3-4) of back feathers. The feathers must be quite substantial, restricting the species for which it is suitable.
In both tape and glue-mounting, it is important only to attach the tag to fully-grown feathers with a fully hardened shaft. This rules out the methods for birds in active body moult and is usually not appropriate for birds that are about to moult, unless the tag deployment is very short. 

8.4.2 Tail-mounted tags

For short-term deployments, fixing a tag to a bird's tail is usually the safest method to tag a bird. No harness is required, and the tag will be lost at the next moult. 

Tail mounts are necessarily positioned further from the bird's centre of lift, and therefore should be lighter than backpacks. The rule of thumb for tail mounts is 2% of a bird’s body weight.

Tags are usually attached to just one or two tail feathers, with glue and/or thread. For some larger species, especially seabirds, single-sided adhesive tape is used. 

It is even more important with tail mounts than backpacks that the feathers are full-grown with fully hardened shafts. As with other feather-mounting, the applicability of the method is critically dependent on the timing of moult.

8.4.3 Leg-mounted attachments

Leg-mounted tags are most often used on waders and seabirds for the attachment of light geolocators, which do not have antennas. However, radio tags (VHF tags) with external 'whip' antennas can also be used on some species, either with the antenna extending horizontally or, on long-legged species, with the antenna running parallel to the leg. In the case of horizontal antennas, care must be taken with antenna position and angle, to avoid the risk of birds tripping over the antenna when they walk. 

Leg-mounted radio tags are sometimes used for short-term tagging when tail mounts are unsuitable (e.g. raptor or owl nestlings with growing tail feathers). 

Leg-mounted GPS devices are rarely used, mainly because the technology currently does not suit this form of attachment, where the tags must be especially robust and solar panels and antennas have a poor view of the sky/satellites.

Leg ring with device

This typically comprises a conventional plastic leg ring with a tag affixed using thread, glue, or a plastic cable tie. Care must be taken to avoid creating protrusions inside the ring (e.g. from a cable tie) that could abrade the leg. Using thread or glue can also allow the tag to eventually detach, ideally after it ceases to function.

Leg flag with device

A leg flag is a rigid plastic leg ring with an extending flange (the ‘flag’) to which a tracking tag is attached. Positioning the tag on the flag, further from the centre of the ring increases leverage on the ring and can exert excessive pressure from the ring edges against the bird’s leg. For this reason, such fixtures must be carefully designed so that the tag remains lightweight and positioned as close as possible to the main body of the ring. Depending on the species, it may also be advisable to place a ‘spacer ring’ below the leg flag to counter this risk.

Temporary leg-ring mounts

For short-term use, instead of rings, tags are attached with straps, glued or riveted around the leg. Like falconry 'jesses', these are normally made of leather, but for smaller tags a faster degrading material such as waxed cardboard may be employed. These materials degrade naturally, causing both the ring and tag to fall away.

PIT tag on leg ring

PIT tags - Passive Integrated Transponders - can be attached to standard colour rings, but are usually bought as complete assemblies, where the PIT tag is integrated into a dedicated plastic leg ring. Although leg-mounted PIT tags are included here with tracking devices, their signal range is so short (usually a few centimetres and very rarely as much as a metre) that they are more correctly considered as being for ID only, not tracking.

8.4.4 Neck-mounted attachments

There are two basic forms of neck attachment: necklaces, usually comprising a soft narrow cord, and neck collars/rings, which are based on conventional numbered neck collars/rings traditionally used for ID of geese and swans. 

Neck collar without device

These are rigid plastic collars/rings engraved with individual codes, typically used on long-necked species such as geese and swans. These collars overlap for sealing and are commercially available in acrylic material.

Neck collar with device

Historically, a tracking device would be glued and bound (often cable-tied) to a standard plastic neck ring/collar. This is sometimes still done, but more usually nowadays the tracking electronics are integrated into a purpose-built package by tag manufacturers. 

Necklace with device

Most often used on Galliformes, where they have been shown to be safer than harness-mounted backpacks, these are tags fitted with a cord or similar material that runs around and hangs on the bird's neck. Care is needed when setting the loop diameter: if too large/loose, the tag can hang in the way, fall off, or the bird may trap its bill or foot when preening. If too tight, the necklace may obstruct swallowing of food items, which can be surprisingly large (e.g. female Galliformes swallowing large snails as a calcium source during egg formation).

8.4.5 Flags, tags, and rings for identification

These are for visual ID only and do not include any form of tracking device.

Colour ring

This is either an engraved plastic ring or a combination of smaller coloured rings, typically used alongside a standard metal ring to uniquely identify an individual.

Leg flag without device

Leg flags are rigid plastic rings with two projecting tabs that are cemented together to close around the leg. They are usually fitted on the tibia for optimal visibility in feeding birds, though sometimes placed on the tarsus for visibility in roosting birds. Leg flags are more conspicuous than colour rings, increasing the likelihood of resighting. They may be engraved or used with colour-ring combinations for individual identification. Although some species may in theory be large enough to carry two tibia flags, there are no current projects approved for more than one flag on an individual bird, and only the minimum number necessary should be used.

8.4.6 Other external marks and tags

Patagial tag without device

This is a flexible, coloured and numbered plastic tag (e.g. PVC) attached through the patagium (the skin fold at the leading edge of the wing). Produced in various shapes and colours, they have been widely used on raptors and other species. Birds tagged before fledging may accept the tag as if it were an additional feather.

Patagial tags can also carry tracking devices, but these are used almost exclusively on very large, soaring raptors, especially condors and other vultures. They have therefore not been licensed by BTO. 

Web tag

A small metal tag attached to the webbing of the foot, used to mark individuals too small for a metal ring. A standard ring can be fitted later when the bird has grown.

8.4.7 Non-device markings and samples

Sampling

This includes feather clipping, feather pulling, or swabbing of feathers, feet, cloaca or mouth.

Plumage marks

These are temporary markings used to identify individuals (e.g. within a brood) or cohorts. Markings are applied with waterproof markers (e.g. Sharpie) or sheep dye. These have been used successfully on waders, seabirds, and other species to enhance resighting and recovery rates (Calvo & Furness 1992). In the past, more hazardous dyes (e.g. picric acid, Rhodamine B, Malachite Green, Nyanzol A/D, and various clothing or hair dyes) were used. Paints and correction fluid should be avoided as they can damage feather structure. Plumage marks fade within months due to weathering and are shed completely during moult.

8.4.8 Special traps

Note that live vertebrate bait cannot be used by BTO ringers.

Bal-chatri

A domed cage containing bait, which could be a sound lure or dead prey item, covered with nooses to entangle feet and legs. Must be either weighted or secured to the ground. Used for birds of prey.

Dho-ghaza net

A large panel of net loosely set on poles so that it collapses and travels a short distance on capture, gently wrapping a fast travelling bird in flight.  Bait, such as a sound lure or dead prey item, placed either inside of a square (Cube-Net) or on an appropriate side of a single net. Typically used for fast flying birds of prey.

Drop lid trap

A large cage trap with a separate compartment at the bottom containing a decoy/lure/bait, with a perch above it. As the target enters the trap and lands on the perch the lid is triggered and drops securely trapping the target inside. Similar to a potter trap, but vertical. Typically used for birds of prey.

Noose carpet

A mesh square with nooses tied at regular intervals to entangle legs and feet. Must be secured to the ground. Frequently used around nesting birds, particularly but not limited to, gull species. In such cases care should be taken to avoid damage to eggs/chicks.

Pole noose (pole-mounted noose trap)

A rarely used method to capture raptors which takes advantage of birds that will perch on an elevated structure near the nest. The pole is set near the nest of the bird, and when the bird lands on the pole, the head of the pole is moved downwards by the weight of the bird, which triggers the noose to close around the bird’s leg. 

Purse net

A net used to catch individual burrow-nesting birds, i.e. Puffin, Storm Petrel, Manx Shearwater. A pocket of netting staked down over the burrow entrance which pulls closed as the bird enters or exits the burrow.

Trammel net

Small mesh netting is ‘set’ between two panels of larger-mesh netting such that a bird running through the larger mesh then pockets in the smaller mesh netting and can’t reverse out. Generally used only on Corncrake.

Pneumatic net

Rarely used technique similar to a cannon net, but using compressed gas instead of black powder to fire a large net over birds.

Net gun

A packed net, weighted at the corners, fired from a hand-held compressed CO2 device to target individual birds difficult to trap by other means, i.e. corvids and seabirds, or birds where a portable system is required. 

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8.5 Likelihood of approval of methods

8.5.1 Approval matrix

This summarises the suitability of each method for each species group, and therefore the likelihood of approval, based on current evidence at the time of publication. Section 8.9 provides more detailed information on each group, and detailed information for each species will be provided in the species pages as they are developed and published.

Table 8.2: Approval matrix

Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on this species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

8.5.2 Methods where approval likelihood is the same across all species and groups

Plumage marks 

No known issues with marks on any species or groups, though note that red marks should be avoided as these can be mistaken for blood.

Samples

As long as the guidelines (agreed with the Home Office) are followed and training is completed, these methods will be approved on all species.

Colour ringing

Whilst there are some species where issues are known (for example, Hawfinch chicks should not be colour ringed as they are likely to be removed from the nest by the adults) colour ringing is a safe method on almost all species. 

8.5.3 Methods which are not approved by BTO

Nasal tags and saddles

Coloured flexible plastic or rubber tape folded over the top third of the upper mandible and held in place by metal wire or nylon monofilament passing through the nasal opening. These are not approved for use by BTO/SMTP due to concerns about the risk of injury or death from entanglement, for example from aquatic vegetation. They are, however, used in other countries to mark waterfowl, particularly surface feeding ducks.

Implants

Includes subcutaneous or intraperitoneal implants or, more often, tags attached to subcutaneous anchors on the back of wildfowl. Due to the invasive nature of the attachment, an ASPA licence would always be required. 

Cut claw

Although this has occasionally been allowed in the past, due to the risk of bleeding and infection should an incorrect cut be made, this method is unlikely to be approved unless there is no other viable option, and the ringer has been trained to carry out the procedure safely by a veterinary professional.

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8.6 General principles/project design overview- selecting your method

Applicants are advised to consider the points below, and ensure that they explain why they selected the method applied for (including why the attachment method was selected, and why the device was selected, if relevant). It is helpful to explain reasoning and the thinking behind project design.

1. You should select the safest and most well-established method on your study species that will enable you to answer your research question. If using a device, temporary device attachments (e.g. to feathers) usually carry less risk than permanent attachments (e.g. harnesses), so should be selected if long-term data are not required.
2. If using a device, the attachment should ideally not last longer than the tag is expected to provide data, as it is not desirable for a bird to be carrying a device that has stopped providing data.
3. When deciding on a method, consider the likelihood that you will succeed in collecting the required data - depending on the method, factors influencing this include:
   1. Tag performance - including transmission, feather shading, battery life.
   2. Resightings - do you have a suitable plan in place to resight colour marks? Does the species behaviour make resightings likely? Do you need to consider using technology, such as camera traps, or engaging the wider public?
4. Consider how you will evaluate the safety of the method - for example, do you need to include a colour marked control cohort? You should also consider how you will evaluate any impact on breeding outcomes. If you are recording details of nesting attempts, please consider submitting this information as nest records, which are extremely valuable to BTO.

The following papers contain useful information about the specific study species concerned, but also provide examples of study design, the testing of materials and the level of detail needed with regard to materials to ensure repeatability.

Fijn et al. (2024) - this paper on terns includes a good example of testing the rate of deterioration of potential harness materials in different conditions.
Langlois Lopez et al. (2023) - this paper on Great Black-backed Gulls includes useful information on assessing the impact of tagging on breeding success.
Clewley et al. (2022) - this paper on Kittiwakes shows an example of how different harness styles can have different impacts on birds.

8.7 Tracking and logging devices

Tracking technology has evolved rapidly, with significant advances in recent years and further innovations are certain to follow. The categories and details provided here (including indicative lightest tag weights) represent a snapshot of current tracking devices and should be used as a general guide only. For the most up-to-date specifications and options, consult the websites of equipment manufacturers and suppliers. 
Tags are grouped below according to their function and mode of operation. Some technologies that are experimental or rarely used have not been included in the main tables but are listed later in the document.

8.7.1 Signal-only tags

Tags in this category do not collect data. They transmit simple radio signals to local receivers, which may be handheld units, vehicle-mounted, or stand-alone stations. Their range is relatively short (and in the case of PIT/RFID, extremely short), but they are very lightweight and consume little power, allowing for long operating lives. 

Signal-only tags are most often used on small passerines, where GPS or satellite tags would be too heavy. They include traditional radio-tracking (commonly known as VHF tracking), where each tag has its own frequency and is located manually by way of a tracking receiver and handheld directional antenna. These tags are best suited to studies of local bird movements and habitat use. 

More recently, coded VHF or UHF tags that share a common frequency have been developed for use with automated arrays such as the Motus Wildlife Tracking System. These tags, optimised for automated detection, are less suitable for manual tracking, but their slower pulse rates greatly extend battery life, allowing them to operate for much longer periods to track migration, stopover ecology and survival in regions where Motus logging stations are situated.

Unless otherwise stated in the table below, these tags are usually glued to the bird’s tail or harness-mounted or glued on its back. 

Table 8.3: Signal-only tags

8.7.2 Data-logging tags

Most modern tags collect and store location and other data on the device itself, and these data are either downloaded directly from the tag, or transmitted remotely to local receivers, ground-based or satellite-based communications infrastructure. 

As tags become more sophisticated, particularly when remote communications are added, they also become larger and heavier. The size increase is due less to the extra circuitry, than to greater power demands, which require larger batteries to achieve a useful lifespan.

Archival tags (retrieval required)

Sometimes referred to as “store-on-board” tags, these devices must be retrieved to access the data they record, which is their main limitation. Their main advantages are small size and weight, and low power requirements compared with tags that transmit data. 

For location data, archival devices fall into two main types: GPS loggers, which provide precise positions, and light-level geolocators (GLS - Global Location Sensor), with which positions are estimated from ambient light (using times of sunrise and sunset) to an accuracy of a few hundred kilometres. Both types can be combined with additional sensors, such as temperature, barometric pressure (altitude), submersion pressure (dive depth), accelerometers and magnetometers. Some tags have no capacity to determine location but carry only sensors; for example, Time–Depth Recorders (TDRs) used to measure dive profiles.

Table 8.4: Data-logging tags

8.7.3 Short-range data-transmitting tags

These are tags that log and then download data to a fixed base station or handheld logging receiver over ranges of hundreds of metres to several kilometres. The receivers are usually dedicated to an individual project, rather than part of a larger communications network. If the spatial range of the birds is relatively small, and especially if the study is long-term (e.g. one year or more), fixed stations can be used to collect data autonomously. If tagged birds are more widely dispersed, range over larger areas or the study is for a short period (e.g. breeding season only), it may be more cost-effective to track birds on foot and remotely download their data to a handheld receiver. Usually, different receivers are used to track and download data. The major advantage of data-transmitting tags is that data can be collected without the need to recapture birds. Their disadvantage is that data transmission requires higher power, which necessitates a larger battery and results in less data per unit tag weight. 

There is usually two-way communication between a tag and a receiver, which enables more energy-efficient data transfer (the tag ‘knows’ when its data has been received and doesn’t have to repeat transmissions). Two-way communications also allow for data collection schedules to be changed remotely. 

Table 8.5: Short-range data-transmitting tags

8.7.4 Terrestrial mobile-network tags

One of the most widely used methods to communicate remotely with tags is via the terrestrial mobile phone network. Early tags communicated over 2G or 3G GSM networks, via SMS text messages or low-rate GPRS data connections. As 2G and 3G networks are phased out, newer tags increasingly use LTE-M and NB-IoT technologies within the 4G/5G framework. These standards send data packets directly to the internet using energy-efficient, low-bandwidth protocols. They no longer operate on GSM networks and are better described more generally as ‘mobile-network’ tags, although the legacy term GPS-GSM may persist in common usage.

Tags are configured to connect to multiple national networks, similar to roaming mobile phones, and exchange data whenever they come within range of a mast. The main limitation of mobile-network tags is the need for periodic access to network coverage during deployment. They are therefore less suitable for tracking sedentary birds in areas with poor mobile reception, or to study migratory species breeding or wintering in remote areas where coverage is lacking. However, providing the birds survive until their next migration, stored data will be transmitted when they pass through populated regions.

Nearly all mobile-network tags are solar-powered, containing a rechargeable battery that varies in capacity with the size of the tag. They are almost always attached to the bird’s back, usually with a harness.

As they rely on public communications infrastructure, use of these tags usually incurs a service charge. 

Table 8.6: Terrestrial mobile-network tags

8.7.5 Satellite-based network tags

In some ways similar to mobile-network (GSM/NB-IoT/LTE-M) devices, these tags communicate with space-based rather than terrestrial communications networks. This gives them global coverage for data transfer, but as the distances over which they need to transmit are greater, they generally use more power and tend to be heavier. 

Because they depend on the more expensive infrastructure of satellite constellations and their ground-based support systems, they tend to have higher service charges than terrestrial mobile-network tags.

Table 8.7: Satellite-based network tags

8.7.6 Unusual tech

Reverse-GPS (ATLAS, Vildehaye)

These are a form of tag using ‘Time Difference of Arrival’ (TDOA), sometimes called ‘Reverse-GPS’, to provide GPS-level accuracy from light-weight transmitting tags. They require a fairly complex infrastructure of receiving stations and are currently available only as ‘build your own’ tags from open-source hardware and software/firmware. 

ICARUS

The ICARUS Initiative (International Cooperation for Animal Research Using Space) is an international project aiming to track global migratory patterns and behaviour of small animals, including birds, from space. It was initiated by academics at the Max Planck Institute of Animal Behaviour in Germany. Initial trials were based on receivers fitted to the International Space Station (ISS). The main appeal to researchers has been the provision of free tags, to encourage the use and further development of the system and to create Europe-wide studies of individual species, involving large numbers of birds. 

GPS–Bluetooth

The latest version of Bluetooth, known as Bluetooth Low Energy (BLE), is starting to be used for two-way comms to GPS logging tags. Because Bluetooth is so high frequency (2.4 GHz, at the upper end the UHF band), its signal range is relatively short and is severely reduced by vegetation, especially when wet. It is likely best suited to short range logging of birds in flight or at height in open terrain. Such a high frequency enables very fast data transfer, and communications can be via a smartphone (at even shorter range); these are probably the main advantages of Bluetooth use in bird tracking.

GPS–Globalstar.

Globalstar is a satellite constellation used in wildlife research for transmission of GPS and sensor data. It has been deployed rarely for bird tracking because Globalstar modems are quite heavy, and Argos has provided a lighter-weight alternative. However, it has some advantages over Argos that potentially make it attractive for a particular medium-sized range of bird species. 

These tags are, at the time of writing, untested in the UK.

Please note that it is the responsibility of each project lead using devices to ensure that the devices comply with appropriate regulations in relation to transmission power and frequency. Standard transmitters, supplied by most manufacturers or suppliers will already have type approval but if in doubt check with the supplier. If you are using non-standard transmitters, it is your responsibility to ensure that their transmissions are within legal bounds by consulting the Department for Business, Innovations and Skills.

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8.8 Guidelines for the use of novel automated tracking systems

Novel automated tracking systems, such as those described above in section 8.7.7, offer exciting potential benefits, such as GPS-level accuracy, rapid sampling rates (e.g. a location every few seconds), and real-time, remote data collection with small, lightweight tags.

However, SMTP wishes to highlight the importance of understanding and mitigating inherent risks in novel tracking systems before tags are fitted to birds. Experience has shown that even predictable risks cannot be entirely eliminated, and unforeseen issues can arise, particularly for inexperienced users. This section aims to address these concerns and provide basic guidance for safe and effective deployment.

8.8.1 Purpose of this guidance

As described in ‘Criteria for decision making’ in Section 8.1.1, SMTP’s role includes evaluating whether proposed tracking techniques will deliver meaningful data of sufficient value to justify the associated risks to tagged birds. This guidance aims to reduce the risk of tags yielding minimal or low-value data. Although the focus is on reverse-GPS systems, the principles apply to any tracking systems that require custom infrastructure or involve non-standard tags.

8.8.2 Key areas of risk

Two primary areas of risk are associated with the use of these tracking systems:

1. Tag construction
2. Receiving system set-up

Tag construction

Challenges in tag assembly

Unlike commercially produced tags, ATLAS and Vildehaye devices are typically supplied as bare circuit boards and batteries. These must be encapsulated (protected with a resin coating or housing) before attaching to birds. Additional assembly, such as soldering batteries and antennas, may also be required.

Encapsulation and protection

Encapsulation is a critical step to protect electronics from environmental hazards. Proper encapsulation prevents moisture ingress and ensures the tag functions as intended. However, materials like resins can diminish the performance of RF circuits. Basic requirements for encapsulation include:

• Using materials that do not interfere with electronics.
• Ensuring durability under prolonged exposure to water and other environmental stressors.

Antenna robustness

Antennas must withstand potential interference from the bird, including breakage, kinking, or fraying. Strain relief mechanisms at the antenna base can help prevent fatigue from constant bending, especially for long-term deployments. The choice of antenna should be tailored to the species being tagged; for instance, the requirements for a wader chick differ from those for a raptor (two real examples of proposed uses of these tags).

Battery soldering risks

Soldering batteries requires careful heat management. Excessive heat can damage the battery, leading to reduced capacity and shortened lifespan. Indicators of extreme heat damage include melted seals, which signify unsafe soldering methods.

Recommendations

SMTP does not prescribe specific encapsulation materials, antenna designs, or soldering techniques. Instead, users are advised to:

• Seek guidance from experienced users, including the designers of their tags.
• Conduct basic environmental tests, such as submerging the tag in water for several days, to evaluate durability.
• Replicate proven methodologies from similar studies.
• Collaborate with technical colleagues experienced in tag construction.

Receiving system set-up

System optimisation

These tracking systems rely on fixed receiving stations, which must be optimally positioned within the study area. The effectiveness of the system can be influenced by terrain, habitats, and species behaviour, all of which vary between projects.

Testing under realistic conditions

Thorough testing of the system under project-specific conditions is essential:

• Use fully assembled and encapsulated tags during testing.
• Place tags in scenarios that mimic real deployment, such as attaching them to objects resembling the bird's body. For example, use a small plastic bottle or sealed bag filled with 1% saline solution to simulate a bird’s body.
• Test the system across the study area, including at the expected limits of the signal range.

8.8.3 Application requirements

As part of your application to use novel tracking systems, SMTP requires detailed information about your plans to mitigate risks. Specifically, please address the following:

Tag encapsulation

• Describe the materials and methods you will use for encapsulation.
• Provide justification for your choices, such as evidence of prior success in similar studies.

Antenna selection

• Specify the antenna material and design.
• Explain your choice with supporting evidence or references.

Battery soldering techniques

• Outline the methods you will use to minimize heat damage during soldering.

SMTP are unlikely to know for sure that your chosen method will work, though we can provide additional guidance if a proposed material or method is known to be problematic.

Deployment criteria

Tags should only be deployed on birds after the system demonstrates satisfactory performance during testing.  

8.8.4 Reporting requirements

A detailed annual report is particularly important when using novel technologies, as it will help inform future project approvals, and any developments to techniques can be included in guidance materials to help other practitioners undertaking their own projects. Please provide as much information as possible on what worked (and what didn’t!) in your report.

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8.9 Species groups - group specific guidance

8.9.1 Passerines and near-passerines

Table 8.8: Suitability of methods for passerines and near-passerines

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harnesses: small species can generally be fitted with leg-loop harnesses, providing the harness and device do not exceed 3% of the bird’s body weight. Larger species, such as corvids and can be fitted with breastband or tracheal knot harnesses.

Adhesive back: glue. Generally a safe method, so comprehensive applications are likely to be approved.

Adhesive tail: glue or a combination of gluing and tying is used. Tail mounting is not suitable until feathers are fully hardened, so not suitable for pullus.

Leg rings and PIT tags: can generally be fitted to adults and to pulli as soon as the bird is old enough to be metal ringed, providing the device will not exceed the weight limit at fledging. Although PIT tags are safe for most species, one study found that Long-tailed Tits fitted with integrated PIT tags had suffered injuries on the leg carrying a PIT tag, potentially caused by the build up of shed leg scutes and debris under the tag, which birds are unable to reach to preen due to the length of the ring. PIT tagging projects should include a mechanism to monitor birds for similar effects.

Colour Marks

Colour rings: safe method for all species except Hawfinch pullus. Note that Spotted Flycatcher should be fitted with anodised metal colour rings, rather than plastic, and Hawfinch colour rings should not be glued. Applicants will need to consider visibility of rings, depending on habits of birds, and effort needed for resighting.

Patagial tags have been approved by BTO in the past on corvid species, but not in recent decades. A strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Notes on unsuitable methods

Leg flag: taped leg flags on rings have been used in the past though are no longer approved. It is unclear whether rigid flags would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck collar: only suitable for long-necked species

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for passerines and near-passerines, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Web tag: only suitable for species with webbed feet.

8.9.2 Birds of prey

Table 8.9: Suitability of methods for birds of prey

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harnesses: generally suitable for most species in this group, particularly large gliding species. Less evidence of safety for falcons. See paper by Dixon et al. (2016) on Saker falcons.

Adhesive back (glue): not commonly used, but likely to be safe.

Adhesive tail (glued/tied): well-established, safe method on adults. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: commonly-used method.

Colour Marks

Colour rings: safe method. Applicants will need to consider visibility of rings, depending on habits of birds, and effort needed for resighting.

Patagial tags: well-established method, suitable for many species in this group; not suitable for species which rely on a fast stoop (falcons) or silent flight (owls) to catch prey.

Notes on unsuitable methods

Leg flag: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck collar: only suitable for long-necked species

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for birds of prey, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval

Web tag: only suitable for species with webbed feet.

8.9.3 Waders

Table 8.10: Suitability of methods for waders

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harnesses: leg-loop harnesses are generally suitable and safe for waders. Can be fitted to full-sized juveniles, but not pulli.

Adhesive backpack (glued): commonly-used, safe method, providing best practice is followed.

Adhesive tailmounts: none recently approved by BTO, but generally a safe method on other species. Unsuitable for pullus as tail feathers not fully hardened.

Leg flag with device: there have been serious issues with flags with devices attached in the past, so a strong case would need to be made for approval, including reason for using a flag over other attachment methods, and evidence of safety.

Leg rings and PIT tags: few projects previously approved, but generally a safe method on other species.

Colour Marks

Colour rings: commonly-used, safe method. Note that combinations are approved by IWSG.

Leg flag without device: flag without device is a well-established method and safe if best practice is followed, including the use of spacer rings where necessary.

Patagial tags have been approved by BTO in the past for use on some wader species, but not in recent years. A strong case would need to be made for approval, including benefits/necessity over colour ringing or leg flagging, and evidence of safety.

Notes on unsuitable methods

Neck collar: only suitable for long-necked species.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for waders, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Web tag: only suitable for species with webbed feet

8.9.4 Gamebirds

Note the specific guidance around ringing Gamebirds in Section 1.3 of the Guidance.

Table 8.11: Suitability of methods for gamebirds

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: previously, studies have shown increased mortality in Galliformes fitted with harnesses, possibly due to an increased reluctance to fly, and therefore increased predation risk; however, recent studies suggest that fitting leg-loop harnesses may be safe for some species.

Adhesive backpack (glued): not a commonly-approved method by BTO, but generally safe for most taxonomic groups, so comprehensive applications are likely to be successful.

Adhesive tailmounts: none previously approved by BTO, but generally a safe method on other species, so comprehensive applications are likely to be successful. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: no projects previously approved, but generally a safe method on other species, so comprehensive applications are likely to be successful.

Necklace: established method, generally safe for adults if fitted correctly.

Colour marks

Colour ring: no known issues.

Patagial tags have previously been approved by BTO for use on grouse species , but not in recent years. A strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck collar: only suitable for long-necked species.

Web tag: only suitable for species with webbed feet.

8.9.5 Geese and swans

Table 8.12: Suitability of methods for geese and swans

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: breastband harnesses have previously been approved by BTO, but not commonly used. Generally unsuitable for long-necked birds, so other methods are preferred.

Adhesive backpack (glued): commonly used on many species in this group, so comprehensive applications are likely to be approved.

Adhesive tailmounts: none previously approved by BTO, but generally a safe method on other species. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: not commonly used, but generally a safe method on other species.

Neck Collar with device: generally safe for this group of species.

Colour marks/other

Colour ring: safe and widely used on this species group. Note that schemes are approved by WWT/Kane Brides.

Neck collar: generally safe. Note that colour schemes are assigned by WWT/Kane Brides, but projects must be approved by BTO.

Patagial tags have been used in the past, but not commonly used in recent years. A strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: a small number of projects mark cygnets prior to metal ringing.

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species; alternative colour marking and device attachment methods preferred.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for geese and swans, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

8.9.6 Ducks, divers and sawbills

Table 8.13: Suitability of methods for ducks, divers and sawbills

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Adhesive backpack (glued): commonly used on many species in this group, so comprehensive applications are likely to be approved.

Adhesive tailmounts: have been used in the past, but some issues around feather loss and birds severing tails to remove tag, so an application would need to trial on captive birds/show evidence of suitability from projects which have taken place elsewhere/start with a small field trial/explain why another method (e.g. back mounts) was not suitable. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: not commonly used, but no known welfare issues and generally a safe method on other species.

Colour marks

Colour ring: commonly used, safe method. Note that schemes are approved by WWT/Kane Brides.

Patagial tags: have been used in the past, but not commonly used in recent years. Issues reported with previous projects, including tag loss and excessive preening. A strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety. Not suitable for diving ducks.

Web tag: Potentially suitable, but not previously used so a strong case would need to be made for the use of this method over other options (such as applying wax inside a standard metal ring) and evidence of safety would need to be provided.

Notes on unsuitable methods

Harness: not currently considered suitable or safe because of concerns about impact on survival due to harnesses wicking water to the skin and chilling the bird. Would require successful trials on captive individuals before approval.

Leg flags: unclear whether this method would be safe for this species; alternative colour marking and device attachment methods preferred.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for ducks, divers and sawbills, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Neck Collar: only suitable for long-necked species.

8.9.7 Crakes, rails, grebes etc

Table 8.14: Suitability of methods for crakes, rails, grebes etc

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: some previous approvals on Corncrake and Water Rail.

Adhesive backpack (glued): used on several species in this group, so comprehensive applications likely to be approved.

Adhesive tailmounts: none previously approved by BTO, but generally a safe method on other species. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: used on several species in this group, so comprehensive applications likely to be approved.

Colour marks

Colour rings: well-established, safe method for this species group

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species; alternative colour marking and device attachment methods preferred.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for crakes, rails and grebes, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval

Neck Collar: only suitable for long-necked species

Patagial tags: as these marks have not previously been approved for use on this group by BTO, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: only suitable for species with webbed feet.

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8.9.8 Gulls and Fulmar

Table 8.15: Suitability of methods for gulls and Fulmar

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: although harnesses have been used successfully on several species of gull, significant issues were found with Great Black-backed Gull, due to significant nest failure of tagged birds.

Adhesive backpack (tape and glue): although these methods have been shown to be safe for most gull species, it is not safe for Kittwake due to increased nest failure of tagged individuals. There is some evidence of increased nest failure in tagged Fulmar, though these data are from projects with small sample sizes.

Adhesive tailmounts: commonly-used method on species in this group. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: commonly-used method on species in this group.

Colour marks

Colour ring: commonly used method on this species group. Note that Large Gull projects are approved by Peter Rock.

Notes on unsuitable methods

Leg flags: although leg flags have previously been approved for gulls, there have been no projects approved for several decades. Strong justification for the use of flags over other colour-marking methods, as well as evidence of safety, would need to be included in an application before the method could be approved.

Neck Collar: only suitable for long-necked species.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for gulls or Fulmar, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Patagial tags: as these marks have not been approved by BTO for use on these species  for many years, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: although these species have webbed feet, web tagging is not necessary, as metal rings can be fitted to pulli before they leave the colony.

8.9.9 Terns

Table 8.16: Suitability of methods for terns

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Adhesive backpack (glue): tendency of birds to remove devices is reduced by using glue rather than tape.

Adhesive tailmounts: although approved in the past, these have not been approved for some years, so good evidence of safety and efficacy from studies elsewhere would be needed before an application could be approved.

Leg rings and PIT tags: commonly-used method on species in this group.

Colour marks

Colour ring: safe method for these species. Note that Roseate Terns are fitted with an anodised metal colour ring in place of a BTO metal ring.

Leg flag: safe method for these species

Notes on unsuitable methods

Harness: low return rates for harnessed Arctic Tern, which may be due to changes in body mass outside of the breeding season which results in harnesses being too tight, indicate that harnesses are not suitable for Tern species.

Leg Flag with device: previous projects have reported severe issues, including injuries.

Neck Collar: only suitable for long-necked species.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for terns, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Patagial tags: as these marks have not been used on these species in the UK, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: although these species have webbed feet, web tagging is not necessary, as metal rings can be fitted to pulli from hatching.

8.9.10 Auks

Table 8.17: Suitability of methods for auks

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: although this method has been approved once previously for species in this group, it is not an established method, so good evidence of safety would need to be provided before a project could be approved.

Adhesive backpack (tape or glue): commonly-used method on most species in this group, so comprehensive applications are likely to be approved.

Adhesive tailmounts: commonly-used method on species in this group, so comprehensive applications are likely to be approved. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: commonly-used method on species in this group, so comprehensive applications are likely to be approved.

Colour marks

Colour rings: commonly-used method on species in this group.

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck Collar: only suitable for long-necked species.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for auks, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval

Patagial tags: as these marks have not been approved for use by BTO for several decades, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: although these species have webbed feet, web tagging is not necessary, as metal rings can be fitted to pulli prior to fledging.

8.9.11 Cormorant and Shag

Table 8.18: Suitability of methods for Cormorant and Shag

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable or potentially suitable methods

Device attachments

Harness: although this method has occasionally been approved in the past, it has not been used for some decades, and strong evidence of safety would need to be provided before a project could be approved.

Adhesive backpack (tape or glue): commonly-used method on species in this group, so comprehensive applications are likely to be approved.

Adhesive tailmounts: generally suitable, though less-commonly used than adhesive backpacks.

Leg rings and PIT tags: commonly-used method on this species in this group, so comprehensive applications are likely to be approved.

Colour marks

Colour rings: commonly used, safe method.

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck Collar: although this is suitable for long-necked species, neck collars are likely to interfere with the swallowing of large prey items, and therefore be unsafe for Cormorant and Shag.

Necklace: as above, this method is likely to interfere with feeding and thus not be safe for Cormorant and Shag.

Patagial tags: as these marks have not been approved by BTO for use on these species  for several decades, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: although these species have webbed feet, web tagging is not necessary, as metal rings can be fitted to pulli prior to fledging.

8.9.12 Gannet and skuas

Table 8.19: Suitability of methods for Gannet and skuas

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: potentially suitable for Gannet, but unsuitable for Great Skua. As this method has not been approved for Gannet for some years, evidence of safety from projects elsewhere would be needed before this method could be approved.

Adhesive backpack (tape or glue): commonly-used method on species in this group, so comprehensive applications likely to be approved.

Adhesive tailmounts (tape): commonly used on these species. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: commonly-used method on species in this group.

Colour marks

Colour ring: commonly used, safe method

Notes on unsuitable methods

Leg flag: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck Collar: suitable for long-necked species only.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for gannet and Skua, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Patagial tags: as these marks have not previously been approved for use by BTO on this group, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: although these species have webbed feet, web tagging is not necessary, as metal rings can be fitted prior to pulli fledging.

8.9.13 Petrels and shearwaters

Table 8.20: Suitability of methods for petrels and shearwaters 

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods

Device attachments

Harness: previously approved on petrels and shearwaters, though not for several years. Good evidence of safety would be required before this method could be approved.

Adhesive backpack (tape or glue): commonly-used method on petrels and shearwaters, so comprehensive applications are likely to be approved.

Adhesive tailmounts: generally suitable, though less commonly used than adhesive backpacks. Unsuitable for pullus as tail feathers not fully hardened.

Leg rings and PIT tags: devices on leg rings suitable for most species, though there have been severe issues reported with petrel species.

Colour marks

Colour ring: safe for this species group

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck Collar: only suitable for long-necked species.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for petrels and shearwaters, there would have to be a good reason to use them over other existing methods, and tests on captive birds or evidence of safe use in other countries would be required prior to approval.

Patagial tags: as these marks have not previously been approved for use  on this group by BTO, a strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Web tag: although these species have webbed feet, web tagging is not necessary, as metal rings can be fitted prior to pulli leaving the nest burrow.

8.9.14 Herons and egrets

Table 8.21: Suitability of methods for herons and egrets

Key
Y = Well-tested method; approval very likely with a good application
? = Has been used in the past but some issues reported so application would need to show how these would be mitigated for; or not used on these species but used on similar species and therefore likely to be safe; or potentially suitable but not widely or recently approved by BTO
N = Method unsuitable / serious issues reported in the past

Notes on suitable and potentially suitable methods
Device attachments

Harness: have been used successfully on Stork and Crane; harness design must ensure that the bird cannot trap its head in the harness.

Adhesive backpack: no projects approved by BTO, but generally a safe method on other species groups.

Adhesive tailpack: some projects approved by BTO; generally a safe method.

Leg ring/PIT tag: attachment method used successfully on species in this group.

Colour marks

Colour ring: safe for this species group.

Patagial tags: these have been used in the past on this species group, but not in recent decades. A strong case would need to be made for approval, including benefits/necessity over colour ringing, and evidence of safety.

Notes on unsuitable methods

Leg flags: unclear whether this method would be safe for this species group; alternative colour marking and device attachment methods preferred.

Neck collar: although these are long-necked species, neck collars are not suitable for these species as they might interfere with swallowing large prey items.

Necklace: this has previously only been used on Galliformes, as harnesses are not suitable for this group. Whilst necklaces may in theory be suitable for herons and egrets, there would have to be a good reason to use them over other existing methods, and tests on captive birds would or evidence of safe use in other countries would be required prior to approval. As with harness design, care would need to be taken to ensure that the bird can’t get its bill stuck in the necklace.

Web tag: only suitable for species with webbed feet.

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8.10 Special Methods administrative processes

8.10.1 Application and decision-making process

Once an application has been submitted, BTO licensing staff/SMTP will assess the application, and staff may contact the project lead to request additional information. The application may be approved without modification, or it may be approved with modifications and/or conditions. Finally, the application may be rejected entirely, though this is very rare, as there is usually a way of modifying the project so that it can be approved.

If a method or tag is novel or not widely used on a species, the approval is likely to be for a small number of birds initially, in order to test the method/device, and the lead will then be required to report back to SMTP before further birds can be approved.

8.10.2 Project approval and endorsements

Conditions

The conditions which apply to projects fall into two categories - those which apply to fieldwork, and those that apply to reporting. The former are designed to reduce the risks to the birds (either individuals or breeding outcomes) and the latter are designed to provide information on the safety of the method and inform future approvals, either for the project in question or similar projects.

All projects are approved with some generic conditions, which relate to both fieldwork and reporting- for example, following the method as specified in the application, and ensuring that records are kept for who has marked/sampled each individual.

There are additionally some conditions which are applied to a subset of projects, for example, projects fitting devices to birds of prey in Scotland are subject to additional conditions.

Finally, some projects have specific conditions- for example, a project may be restricted to tagging males only, or may be required to collect specific observations on tagged birds and report them to SMTP.

Any conditions which apply to a project will be included in the approval email which is sent to the lead, along with details such as the species, number of individuals approved to be marked in that year, and the names of approved agents. It is the responsibility of the project lead to ensure that agents are aware of the details of the approval so that they can comply with any conditions.

The lead and any agents will have their permits updated with the project permission and the Special Methods endorsement (if not already held) and reissued.

8.10.3 Reporting and Renewals

Project leads are contacted in the autumn by BTO licensing staff and provided with a link to their renewal form(s). Leads should report on all activities carried out within the relevant calendar year by 31st December; if the method is being used during December, an extension to this deadline until 31st January can be requested. If your project is active in January-March, you can continue to use the method until your renewal is processed and your renewed permit is reissued by the end of March, provided there have not been any obvious welfare issues. Reports must be completed, even if no birds were marked and even if the project is not going to continue in future seasons.

The report form is pre-populated with some information about the project(s), including a copy of the conditions for that project. Leads should check that they have met all of these conditions, especially those relating to reporting, before they mark their report and renewal form as complete and ready for review by staff/SMTP.

The form allows leads to indicate if they wish to renew the project for the following year in order to continue marking birds. If they do not, the report will still be reviewed, though less urgently. The project will usually be cancelled at this point. (See ‘zero marking’ approvals below for the exception to this).

‘Zero marking’ approvals

In some cases, a project has finished marking birds, is temporarily not marking birds, or has experienced issues which mean that the marking of further birds has not been approved but there are still tagged birds with tags which are transmitting, or which may still be caught and archival tags retrieved.

In these cases, BTO/SMTP still require reports from these projects to provide information on those birds which are still active in order to inform future approvals of similar projects. This may also apply if archive tags have been fitted for a trial year and the outcomes of the retrieval attempts the following season need to be ascertained before approval for further tagging will be given.

In these cases, the project will be renewed as usual, but with zero as the number of birds approved to be marked that year. This means that the lead will still receive reporting reminders to prompt them to update the outcomes of the birds annually. The project can then be easily amended to allow further birds to be marked, if appropriate.

8.10.4 Amendments and transferring projects

Amendments to projects

These can be made at any point during the year, if the method is being modified during fieldwork, or at the time of reporting/renewal. The project application form should be updated, with the changes highlighted. Requests to make changes to agents only should be made via the specific Agents form. Please note that, depending on the age of your project, you may be asked to transfer details of your project onto the most recent version of the application form when you make your amendment request.

Transferring projects

This should be done at the time of reporting/renewal, unless there are exceptional circumstances. As with amendments to the method, an updated application form will need to be submitted. We expect the new project lead to take the opportunity to review the form and ensure that all aspects are up to date, highlighting any changes. The new lead will ideally be an existing agent associated with the project, or will need to have sufficient experience as discussed in section 8.3.1 How much training is needed?. Once approved, the project will be reissued with a new project code.

8.10.5 Cancelling a project and unused projects

If the lead does not wish to continue marking or sampling birds using the method, the project will usually be cancelled once the report/renewal form has been completed, with the exception of some projects where birds are still active (see zero approval projects above).

If a project has not been used for three years (i.e. has submitted nil returns for three consecutive years) it may be cancelled, or the lead may be asked to submit an updated application form for reassessment if they want the permission to remain active. This will help to avoid any issues where the method approved initially is no longer best practice, or where new information or methods have developed in the interim. 

8.11 References

Clewley, G.D., Cook, A.S.C.P., Davies, J.G., Humphreys, E.M., O’Hanlon, N.J., Weston, E., Boulinier, T. & Ponchon, A. 2022. Acute impacts from Teflon harnesses used to fit bio-logging devices to Black-legged Kittiwake Rissa tridactyla. Ringing & Migration 36: 69-77.

Dixon, A., Ragyov, D., Purev-Ochir, G., Rahman, Md. L., Batbayar, N., Bruford, M. W., & Zhan, X. 2016. Evidence for deleterious effects of harness-mounted satellite transmitters on Saker Falcons Falco cherrug. Bird Study 63: 96–106.

Fijn, R.C., van Bemmelen, R.S.A., Collier, M.P., Courtens, W., van Loon, E.E., Poot, M.J.M. & Shamoun-Baranes, J. 2024. Evaluation of tag attachment techniques for plunge-diving terns. Ibis 166: 1003-1022.

Langlois Lopez, S., Clewley, G.D., Johnston, D.T., Daunt, F., Wilson, J.M., O'Hanlon, N.J. & Masden, E. 2023. Reduced breeding success in Great Black-backed Gulls (Larus marinus) due to harness-mounted GPS device. Ibis 166: 69-81.