In early August this year I finished five months of fieldwork studying the breeding biology of the common buzzard. Over this period I located the nests of 36 buzzard pairs and followed their fortunes through the breeding season until they either failed or fledged. ‘South West Peregrine’ have kindly asked me to write a little about this monitoring project and the aims of the research.

Two Young Buzzards
Two young buzzard chicks with the remains of a squirrel in the nest

To start, a little about me. I have been interested in buzzards since first being introduced to the world of raptor research by BTO ringing trainer David Anderson during my MSc. One of the things that attracted me to studying this species was that, considering that they are one of the most abundant large predators in the UK, these birds have been little studied. Buzzards are also an excellent model species to investigate wider questions concerning predators and prey selection. In 2013 I was given the opportunity to come down to the Cornwall campus of the University of Exeter to study for a PhD with the supervisory team of Professors Robbie McDonald, Stuart Bearhop and Steve Redpath.

George Swan
Myself at one of the nests following ringing. You quickly get used to heights when working on buzzards, this nest was 50ft high and the tree was swaying horribly.

One of the areas that we are interested in is how buzzards, with such a broad dietary range, decide what to hunt given that each prey species will require different searching, hunting and handling strategies. Ultimately it would be great to try and answer the question: do individual buzzards display preferences for certain types of prey? These are known as foraging or dietary specialisations. There has been anecdotal evidence of this from elsewhere (see this BTO blog from earlier in the year). The observation of individual foraging specialisations would create further questions, for example: what are the costs and benefits of specialising against staying a generalist? The question of whether buzzards specialise on certain prey is also pertinent to the on-going debate surrounding buzzard predation on released gamebirds. Impartial evidence as to whether these specialisations exist and how they develop may help inform this debate.

Three chicks and Rabbit

A chick with it’s back to food is a rare sight on any buzzard nest, to have three chicks ignoring food is quite remarkable. This pair of adults achieved it by bringing in lots and lots of rabbits. Here, the female is standing on a pile of three young rabbits all brought in over the last few hours.

In order to look at dietary specialisations in a predator you need to understand two things: (1) what they could eat (prey availability) and (2), what they are or have been eating (diet). Although there are various methods to estimate the abundance of prey species, observing the diet of known individuals can be very difficult. The great thing about buzzards is that during the breeding season they bring prey back to the nest whole. This allowed us to explore the diet of different pairs through both the prey remains found on the nests and through recording the adults returning with prey using surveillance equipment.

OLYMPUS DIGITAL CAMERA

One of the nest cameras in action

While collecting this information, the welfare of the birds was paramount. To ensure there was no danger of chick explosions (when the chicks fly from the nest early due to disturbance) we gave ourselves a conservative ringing window of 8 days when the chicks were between 18-25 days old. To further minimise harm we also avoided any work in wet or cold weather conditions. This meant that all the sunny days through June and July I was racing round as many nests as possible ringing the chicks and setting up cameras. Now that it’s over, I can look back on the 2015 field season with rose-tinted glasses but at the time it was hard work!

Snake eggs3

 Watching buzzard nests over hundreds and hundreds of hours of video you get to see some pretty interesting things. Here the female had bought a large grass snake back and proceeded to feed the chick the 10+ eggs she pulled out of it!

The following month was spent lugging huge batteries around the Cornish countryside to keep the cameras running. One of the nice things about our cameras (Supplied by Mike from HandyKam.com) was that the recording box was at the bottom of the tree. This reduced time spent near the nest during the weekly battery changes. The cameras recorded footage every time a chick or parent moved on the nest. Within a month I had over 200,000 videos, consisting of over 4000 buzzard hunting hours and over 1500 prey item deliveries. I don’t want to give too much away here as I’m just starting to analyse the dataset but I’ve included some nice snippets from the footage above. If you’d like to see some more nest camera highlights you can find them by searching #buzzarddiet on twitter. I’ll keep SWP posted with further results as and when we publish them.

In the mean time, we colour-ringed over 40 chicks with an orange ring with a 2-digit code on their right leg, if anyone spots one of these birds please get in touch g_swan@exeter.ac.uk

George Swan

Three birds

Both Adults on the nest present a chick with a mole.

“If you’re interested in this study, here’s a link to George’s 2011 MSc Thesis on buzzard breeding ecology in Scotland. “

Thesis