Rough-legged Buzzard (Buteo lagopus)

The fortunes of all raptors are determined ultimately by the abundance or otherwise of their prey, but few species show this quite as obviously as the Rough-legged Buzzard. This is a bird of the northern tundra and it feeds mainly on voles and lemmings. Both of these mammals have distinct cycles of abundance which include years of boom and bust; on average there is a peak every three or four years, followed by a collapse. In boom years, when small mammals can be literally thick on the ground as they try to move away from their own untenable pressure of population, the buzzards respond by laying more eggs than normal (5-7 as opposed to 2-3). And because the rodents keep on producing litters throughout the summer, the resulting young are likely to prosper, with high numbers reaching the fledging stage, raised on easy meat. In good years the Rough-legged Buzzard may also breed far to the south of its normal range, and at the end of the season large numbers may spill further down than usual to winter in temperate climates.

By Walter Siegmund (talk) – Own work, CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=3408643

In lean years food can be hard to find, and the Buzzards might then be forced to search for more difficult prey, such as birds, in order to keep going. Even then the older chicks within the reduced broods sometimes kill and eat their younger siblings to make up for the lack of food. Before they attempt to breed in poor years birds may travel far across the tundra searching for anywhere with a moderately suitable rodent supply, and many do not even try.

In many other aspects of its life the Rough-legged Buzzard resembles the Common Buzzard, although it hovers more while it is searching for prey, and most often nests on the ground, on a tundra hummock or rocky outcrop.

From ‘Birds: A Complete Guide to All British and European Species’, by Dominic Couzens. Published by Collins and reproduced with permission.