AN ASSEMBLAGE OF 13 COMMON BUZZARDS BUTEO BUTEO (L., 1758)

Paul Whitehead

The visibility on the morning of Monday May 27th 2002 was exceptionally clear, the sunlight strong and the atmosphere humid. At 1106 hrs BST at Little Comberton (SO94), hearing the resonant concerted call of a Carrion Crow I glanced up to see a Common Buzzard heading strongly east at about 25m height. To the north of it were two others also circling to the east.

I then noticed two spirals of raptors mostly near the tops of high thermals, thought to be at about 700m in height, also in the east. Using binoculars I could not make these into anything other than Common Buzzards; the birds were in close contact, tumbling and swirling together off the thermals.

Birds of the Western Palaearctic refers to Common Buzzards assembling in numbers during the breeding season, and with their increasing population in midland England, it is something that has already been noted elsewhere, and that might be observed more often. It is their great visual acuity and marked site fidelity that may bring them together in this way in the breeding season, probably as part of the mechanics of territory maintenance, or the testing of territories by non-breeding individuals.

The ten birds on the thermals were in no hurry to go anywhere and were watched for some 10 minutes after which they gradually dissipated and became harder to track. One bird of this group, which was tracked, demonstrated interesting behaviour known by glider pilots as 'porpoising.' This bird came off the top of its thermal in a steep closed-wing dive of perhaps 20m, heading north towards Pershore, accelerating upwards each time a new thermal was encountered, a process repeated several times during which it eventually covered a couple of kilometres rapidly with no visible wing-action and minimal energy-expenditure.

P.F. Whitehead, Moor Leys, Little Comberton, Pershore, Worcestershire WR10 3EH