Understanding movements and ecology
The Goshawk is an intriguing raptor, as a powerful but normally elusive species. Nationally, it is still a scarce breeding bird, protected under Schedule 1 of the Wildlife and Countryside Act 1982, with a population considered to be far below carrying capacity in most regions. Apart from nest protection, as a generalist raptor, prey availability is unlikely to be severely limiting at present, though survival and recruitment may be key operators. But currently very little information is available on demographic rates for Goshawks in the UK and indeed, no basic, objective information is available on how the species interacts with the countryside, where it may incur risk. In 2015, the BTO began a programme of research on Goshawks aimed at improving our understanding of the species through its movements and ecology, by assessing lowland forest and farmland dependency. This work centered on the Thetford Forest in the Brecklands of East Anglia, where the Goshawk breeding population has been monitored closely for years and where forest management is sympathetic to the protection of nest site habitat. After fledging, however, virtually no information was available on this 'forest' species' behaviour, its scale of movement or its reliance on non-forest habitats. To address the knowledge gap we began a project that would improve our understanding of the way Goshawks interacted with the lowland countryside.
We began in 2015 with a brief study of prey selection when feeding chicks. Small nest cameras were installed on three nests and used to identify delivered prey species. Items at nests were usually ‘pre-processed’ but identifiable. Of these, Grey Squirrel contributed over 60% of items, with Woodpigeons and corvids (typically nestlings or juvenile Carrion Crows or Rooks, plus adults of Jay and Magpie) being important too. Other species included Green Woodpecker, Rabbit (especially at one nest) and Red-legged Partridge. The data are summarised in Fig. 1. This prey-base is biased towards only those prey items that the birds return to the nest with but the findings suggest that, currently, Breckland Goshawks are unlikely to be limited by prey availability at this stage in the annual cycle.
Figure 1- A 2017 update of the breakdown of 129 prey items found on or by Goshawk nests in the Brecks.
Tracking studies: investigating dispersal, home range, habitat use and dependency on forest and farmland
In 2016 we began a tracking programme using the ‘Movetech’ bird-tracking system, a bird-borne method where high precision GPS positions are transmitted via the mobile phone network. The system can help identify habitat use, roosting sites, scale of movement and provide home range estimates. Tag batteries are topped up by solar-power so gaps in the data can occur during long periods of dull weather. Initially, GPS tags were fitted to five juvenile Goshawks from five different nests, under the ‘Breaking New Ground’ project, supported by the Heritage Lottery Fund. A summary of the 2016 tagging project is available via: Henderson I., Conway G. 2017. Exploring the lives of Goshawks in the Brecks: identifying patterns in nest behaviour, habitat use and movements within and beyond the Brecks. Journal of Breckland Studies, 1, 19-27.
In 2017, a further five juvenile Goshawks were tagged (from four different nests) along with four juvenile Common Buzzards from three nests within the forest. Common Buzzards were able to carry identical tags to Goshawks so their contrasting styles of behaviour (furtive vs soaring) can help us interpret tag performance. Common Buzzards are also vulnerable to the same sorts of human-related mortality risk as Goshawks. Updates are provided below.
The Goshawk population in the Brecks is closely monitored by several dedicated individuals, with special thanks given to Bernard Pleasance and Simon Evans in this regard. We are also grateful the Neal Armour-Chelu and Rachel Riley at the Forestry Commission England for their interest and background support. Funding for the 2016 Goshawk tagging project was via the ‘Breaking New Ground’ Landscape Partnership Scheme in the Brecks, supported by the Heritage Lottery Fund. In 2017 we gratefully received funding via The Sound Approach.
Tracking summary, to September 2017
Four of the five Goshawks (two males and two females) are doing well. A fifth juvenile died in the nest-wood at about 30 days after fledging, from what looked like predation (eg., a fox or another Goshawk). The tag was retrieved undamaged. Overall, survival into September was good. All birds moved off the forest onto farmland or farmland-forest edge. After the initial phase of dispersal the females have tended to be less mobile than the highly active males.
Two of the four Common Buzzards are still active, mainly on farmland, occasional drifting far and wide in high pressure weather. One from, Kings Forest, is currently near Newmarket having first visited Reepham (north of Norwich), then Hadleigh (south Suffolk) and Cambridge. The other bird, from Cranwich, visited Huntingdon, then Fressingfield (Suffolk), then the Fens for many days before returning to Cranwich only recently. Two other buzzard tags have not transmitted since July, though after having left the nest itself. The birds probably have died within their natal wood (given their age) and therefore probably due to natural causes. Officially, the outcome for both individuals is unknown but searching will continue as the forest field-layer recedes.
Goshawk updates spring 2018
Three of our five Goshawks survived the winter, two females and one male. Sadly one additional male that had been very active all winter died in February after having collided with a car. It transpired, however, that this individual was also carrying avian influenza. The corpse is with Defra (via ZSL) as we wait to hear what the official cause of death was. Defra (via ZSL) also have the tracking data as obviously ther are questions as to how and where the bird contracted the virus.
Of the surviving individuals, all three settled into a regular winter home range in and around the Brecks, with the male generally being more adventurous. But through spring all three expanded their range, often moving back into the forest and frequently interacting with known territories during the displaying season. In one female, this triggered an extraordinary journey that pretty much circumnavigated East Anglia (see tracks), before returning to the Brecks. We wonder if this individual would have crossed to the continent had the sea not appeared so daunting?
Since April all three birds settled back into their more familiar winter pattern, albeit with a stronger focal point for the two females. The male is unlikely to breed in its first year but it is possible the females are now paired up…
Image: Tracks for three Breckland Goshawks, two females (red and green), and a male (blue), as of end April 2018. All three were hatched in 2017. The green female took a 20 day tour of East Anglia between 16th March and 4th April, visiting Rendlesham and Dersingham before returning to the Brecks.
Buzzards: Our remaing active Common Buzzard, we think, is still living at Exning by the A14 but unfortunately the tag is not working well and only transmits infrequently, so we lose contact for long periods.