How to record a nesting attempt

Bullfinch pair with young. John Harding 

This page explains what you should record when visiting a nest. For information about submitting data please refer to Demography Online (DemOn) guidance.

To collect the most useful information about a nesting attempt, it should be visited at regular intervals until no live eggs or young remain in the nest. If a nest is found at a later stage (with hatched young, for example), simply start monitoring from that point, but please only report nests that are being actively used. Any record consisting of two or more visits is of value and accurate details of eggs, young and the outcome of the nest are particularly useful.

The Code of Conduct must be followed at all times. 

Counting nest contents

To ensure that all the eggs and young are counted, it may be necessary to carefully move one or more eggs a fraction to reveal any that are hidden deeper in the nest cup. If this is done, ensure the nest contents are left as they were found, including any material that was covering the eggs or young.

Accurate counts of nest contents provide the most useful information, but this isn’t always possible, in which case you can use approximate counts.

  • If you can see some eggs or young in the nest but think there is likely to be more: record the number visible followed by + (for example, ‘6+’ if you could see 6 eggs).
  • If you cannot see the contents due to an adult sitting on the nest: record this with '?' 

Using status codes

The status of a nest, its contents and the adult birds can be recorded for each nest visit. Statuses are recorded using 'status codes', which describe the different stages and conditions you may find. 

For example, if you visited a nest and found a full clutch of warm eggs and a sitting parent that left the nest on your approach, you would record the fact that the eggs were warm (WA) and that a parent was incubating (AN). If you visited the nest at a later date and found the remains of predated young, you could record the fact that the nest failed at the young stage due to predation (JP). You can select the status from a drop-down menu in DemOn when you input your records.  

You can see a full list of the status codes and their definitions on the NRS Coding Card. If you want to refer to the status code definitions while out in the field, you can download the Coding Card to your smart device or install the BTO Ringing Information app from the App Store (for Apple devices) or Google Play (for Android devices).

Recording nest outcome

In order to see how successfully birds are reproducing, we need to know the outcome of each nest that you monitor. Every nesting attempt will either result in 'success' or 'failure': 

  • If at least one young from a brood is deemed to have fledged a nest, then we consider that nest to be a ‘success’.
  • If a nest fails to fledge even a single young bird, then we consider it to be a ‘failure’.

Most of the time you will be able to judge the outcome from the evidence found at the deserted nest. For example, you could conclude that a nest had failed if you found a brood of dead young lying in the cup, or if you found the nest entirely pulled apart with no live young present only days after hatching.  Alternatively, you might conclude that a nest was successful because you found it intact and empty just a few days after seeing the young almost ready to fledge. If you know that only some birds fledged, adding a 'failed' outcome code is useful, as it allows us to see what has happened to the eggs or young which didn't survive. 

The status codes for nest outcomes can be found on the NRS Coding Card

The visit at which you first conclude that a nest has succeeded or failed should be your final recorded visit. Please do not record subsequent visits to the nest, such as visits to a nestbox in Autumn to clean it out, or sightings of fledged young weeks later when passing the nest site. If you do visit an old nest and it has fresh eggs, this will be the start of a new record.

What to record if you're unsure of the nest outcome

You may be unsure of the nest outcome if you find an empty nest and are not confident about whether or not the young actually fledged, or if you began monitoring a nest but could not continue making visits.

In these cases, you can record 'Outcome Unknown' (OU) on the last recorded visit to the nest. 

If you monitor the nest of a nidifugous species (which leave the nest very soon after hatching), such as a wading bird, you would normally finish the record with ‘OU’ because it is not possible to follow the young once they have hatched and left the nest.

Frequency and timing of nest visits

A few well-planned visits to the nest can provide all the information you need. In general, if you are monitoring a passerine nest, you should plan to visit every 4 to 5 days, but it is important to understand the different stages of a nest in order to collect the most accurate information: 

  • The laying period can be calculated by the rate of egg-laying, so even if you don’t visit on the day the first egg is laid, two visits during the laying period mean this information can be back-calculated. 
  • Two visits during the incubation period will show completed clutch size and any egg losses which may occur. 
  • Visiting during or just after the hatching period will give the incubation period and an accurate count of the number of eggs hatched. Care is needed because parent birds are often sensitive to disturbance during hatching. 
  • Follow up visits during the nestling period when the young are half-grown and another at three-quarters grown shows how well the nestlings are surviving and gives the number which are likely to fly. If you are a licensed BTO ringer, you should refer to ringing scheme guidance and training with regards to ringing pulli in the nest at this stage. 
  • Care is required during the fledgling period to ensure the young do not ‘explode’ from the nest, causing premature flight. Visiting shortly after the young are expected to fly will give an accurate fledgling date. 
  • Once the young have fledged from the nest, the outcome can be recorded.

The timing of nest stages - and therefore your visits - will depend on the species being monitored. A Blackbird will take only 10 to 15 days to incubate a clutch of eggs, whereas a Sparrowhawk will take 30 to 36 days. The spacing of visits should therefore be planned carefully to suit the breeding cycle of each species and adhere to the Nest Recorder’s Code of Conduct. For more support planning your nest monitoring, visit our Develop Nest Recording Skills page. 

Recording habitat

The type of habitat surrounding the nest may influence a variety of factors such as food availability, competition for nesting sites and predator abundance. These could all have an effect on breeding success. Collecting habitat data allows us to investigate relationships between these factors.

You should record habitat using the habitat codes in column A of the NRS Coding Card. These codes are available from a drop-down menu when you input your data in DemOn, where you can also enter information about the nest site. This covers details such as nest height and orientation, whether the nest is hidden or exposed and the specific location of a nest, for example, in a bush or on a wall. 

Completing a nest record: step-by-step example

Below is an illustration of a nest being followed from nest-building to fledging, with observations being entered into DemOn.  For brevity, the example below only shows visits made every two weeks, not the recommended 4-5 days for passerine nests.

Visit 1

When first inspected on 15 April, the nest looks complete but there are no eggs. The date and time of visit are entered on the top row of the visit details section (right) and the nest code N4 is selected, as the nest is complete but unlined.

Visit 2

Returning on 28 April, an adult Blue Tit flies off the nest, revealing a clutch of eggs. The date and time are recorded on the next row and a count of the eggs is entered in the 'Live' eggs column. Had the eggs not been clearly visible, an approximate count could have been entered, e.g. ‘13+’. Adult activity code FN is given to show that a sitting female had been on the nest.

Visit 3

On 12 May, some of the eggs are hatched. A count of the chicks and the remaining live eggs are both put down (as there is no evidence that any eggs are dead). Status codes NA (chicks naked) and BL (chicks blind) are given to describe the appearance of the chicks. These codes help determine the likely hatching date.

Visit 4

On 25 May, 11 young are still in the nest. Code FM (feathers medium) is used to describe their appearance because the primary feathers of the largest chick are 1/3 emerged from their sheaths. There is also an egg present but it must be dead as eggs hatch within a few days of each other, so 1 is added to the 'Dead' eggs column.

Visit 5

By 8 June, the nest is empty, so an 'outcome' status code is used to indicate that the nesting attempt has finished. Here, the code NE is selected as the nest has every appearance of having fledged young successfully: complete and undisturbed and containing feather scales and droppings from large young.

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