Tagging Goshawks in the Brecks

Breaking New Ground Logo

Breaking New Ground, and ‘Wings Over the Brecks’ project, supported by the Heritage Lottery Fund to identify patterns in habitat use and dispersal within and beyond Thetford Forest.

Nationally, the Goshawk is a scarce breeding species and protected under Schedule 1 of the Wildlife and Countryside Act 1982.  Goshawk is one of the ‘iconic’ species of the Brecklands but the forest environment within the Brecklands is changing in response to forest management and recreational demands, as well as climate change. The Breckland SPA (Special Protection Area) population of Goshawks is considered to be below the number expected but the situation is improving. However, it would be helpful and fascinating to understand habitat use, both within and beyond the forest environment (such as the potential reliance on farmland or heathland) and just as importantly, to understand patterns of dispersal and settlement to other parts of East Anglia.

Heritage Lottery Fund Logo

Famously, the Goshawk is one of our most elusive and furtive birds of prey, whose movements are not amenable to normal visual observation. Literally nothing is known, locally, about this species’ use of habitats, daily movements or home range size (and therefore potential carrying capacity). There is no information on their use of farmland, woodland blocks or created habitats such as heathland.  Only remote tracking of individuals within and beyond the forest, and between seasons, can provide objective insights into such patterns of behaviour, and for this reason we applied for a license to track a small number of Goshawks in the Brecks. The novel ‘Movetech’ GPS tags used do not transmit via satellite, as used on the BTO Cuckoos(see Cuckoo web pages), but use the  mobile phone network to periodically send GPS locations back to the observer. The tags have some limitations, requiring sunlight to charge the batteries and a mobile network signal to transmit the data, but they are expected to operate for around two years. Similar work has been undertaken in Scotland for some years and is on-going involving a larger sample of birds. The two sites will provide interesting contrasts, with the birds moving over such very different landscapes.

Our original aspirations for this project were to fit tag to adult Goshawks in order to estimate home range size and carrying capacity within the Brecks. In the event, we chose to tag older nestling juveniles partly because adults are difficult to catch but mainly because the Scottish Goshawk study, and other raptors studies, have demonstrated that the juveniles accept tags very well.  As such, we fitted tags to five mature nestlings in 2016. The juveniles will provide different information to adults. Rather than home range estimates they will provide information on dispersal and links to other woodlands in the countryside.

Regulation and tag fitting

A 40 day old female Goshawk chick fitted with GSM/GPS tag.

Figure 1 - A 40 day old female Goshawk chick fitted with GSM/GPS tag.

Bird tagging is highly regulated in the UK and all such projects are closely monitored. Prior to commencing a project, it must be demonstrated, to an independent panel of experts, that the proposed tracking device and attachment method are both proven to be reliable and safe to use on the species being studied. There is always consideration given to the justification of tagging, relative to the potential gains in knowledge that may be acquired.  The ‘Movtec’ bird-tracking system is an innovative method of tracking bird movements, by connecting to the mobile phone network.  This technique has been successfully applied to similar sized birds, such as gulls.  Major advantages of this system are that it provides objective, high precision locations and data is regularly fed back over the mobile phone network regardless of how far away the bird moves.

The devices have been used successfully on Lesser Kestrels, amongst bird of prey, obviously in less gloomy conditions than we enjoy in Britain. The devices have not been deployed on a ‘woodland’ bird but similar devices fitted to Scottish Goshawks have relayed information, in once case for over two years.  We would expect to see two years at least out of the tags and technically longer as far as the componentry is concerned.  The harness method used enables the tag to be fitted as a back pack, and is designed to fall off the birds after an undetermined period of time, due to a central weak point attachment using cotton thread. This means that after the tag ceases to operate, the bird will not carry the devices for its entire life.  The harness material is made from Teflon ribbon, a ‘high-tech’, US designed woven tubing that is soft, strong and lies flat to the birds, slipping over the feathers easily. The tag with harness weighs 3% of the body weight of the birds. In the Brecks in 2016, one male and four female chicks were available for fitting (Fig. 1), each individual being from a different nest, for representation across the forest.  The tags were fitted to the nestling at around 30 days old.  All individual’s fitted with tags were later seen to be alive and well, successfully fledging from their nests, which they do from around day 35-40 or more.

Early data gathered

These devices cannot provide minute-by-minute information on bird movements. They should provide several fixes over a period of several days or intermittent days which we can examine for patterns in habitat use and location.

One of our Goshawks began automatically reporting its position soon after leaving its nest in Thetford Forest on 23 July 2016. Over the following few weeks it visited Narborough, Roydon Common and the Sandringham area. The bird was reported to BTO by Sandringham Estate as having been found dead on 9 August, and the tag was returned to the BTO intact. Initial uncertainties surrounding the information received, verbally and via the tag, led to an investigation by the police, who concluded that there were no suspicious circumstances surrounding the bird's death.

High levels of mortality in young birds are a fact of life, and through tracking we can begin to understand just how tenuous the lives of these nomadic young birds may be. In some parts of the UK, mortality in Goshawks is thought to be very high for a variety of reasons, both natural (birds of prey, other Goshawks) and human-related. We knew literally nothing about the survival prospects of Goshawks from the Brecks and so this information will further our understanding. In the meantime, the tracking data has provided some fascinating information on their dispersal, site use and movements. Furthers details will appear both here on the 'Breaking New Ground' website

A female adult goshawk attending her chicks

Figure 2 - A female adult Goshawk attending her chicks.

Plucking post used by adult Goshawks

Figure 3 - A typical plucking post used by adult Goshawks in the Brecks,
before delivering to the nest site.  The prey on this occasion was a Magpie.

Chick diet

In addition to the tagging and attending to another part of the ecology jigsaw for this species in the Brecks, we installed cameras on nests, under license, for the purpose of monitoring daily patterns of nest site behaviour and to identify prey items being fed to chicks (Fig. 2).  At the same time, a log was and is kept of the fragments of prey items discovered at around about the nest site (visited under license) (Fig. 3).   It is pretty clear from Fig. 4 that their principal prey at this stage of the life cycle at least, is Grey Squirrels, making up over 60% of the diet.  However, Woodpigeons and corvids (typically nestlings or recently fledged Carrion Crows, Rooks or Jackdaws, plus Jay and Magpie) are also significant.

Acknowledgements

The Goshawk population in the Brecks is closely monitored as has been the case for decades. This requires strong and devoted volunteer input, with dedicated and knowledgeable individuals who attribute hours of free time to nest finding and nest monitoring – and in particular, we thank Bernard Pleasance in this regard. The Forestry Commission England also maintains a strong interest in the species, encouraging understanding of its use of the forest estate. ‘The funding for the BTO Goshawk tagging project was provided by the ‘Breaking New Ground’ Landscape Partnership Scheme in the Brecks, supported by the Heritage Lottery Fund. For further information about the scheme, visit www.breakingnewground.org.uk’.  We would also like to thank Neil Thomas for tree climbing services, often in his own free time.

A breakdown of 63 prey items found on or by Goshawk nest in the Brecks.

Figure 4- A breakdown of 63 prey items found on or by Goshawk nest in the Brecks.