Diet, nesting density, and breeding success of rough-legged buzzards ( Buteo lagopus) on the Nenetsky Ridge, Arctic Russia.

The rough-legged buzzard, a circumpolar avian predator, is usually defined as rodent specialist in the tundra but as a generalist in the boreal zone, leaving open the question of where the shift in feeding strategy occurs. Here, we investigated the diet and breeding biology of buzzards as well as abundance of their possible prey during 5 years in the low-Arctic shrub tundra on the Nenetsky Ridge, Russia. We employed three complementary methods to assess the diet of this Arctic predator-pellet dissection, identification of prey remains on nests, and stable isotope analysis-to overcome their respective limitations. We documented fluctuations in abundances of the likely prey, namely rodents, ptarmigans, and hares. Nesting density of buzzards changed substantially over the years, but did not track the abundance cycle of the rodents. The number of buzzard fledglings was relatively low (1.08 ± 0.3) and did not change according to the density of rodents. In the year when rodents were at their lowest abundance, diet analyses of nestlings documented a shift from rodents to alternative prey, with a decrease in the proportion of tundra voles and an increase in proportion of hares, ptarmigans, and ducks. Here, we argue that buzzards may adopt different feeding strategies along the gradient from generalists to specialists. While the rough-legged buzzard is usually considered a small rodent specialist, our study shows that it can shift to alternative prey where or when rodents are scarce and when alternative prey are sufficiently abundant to provide subsistence for breeding. [ABSTRACT FROM AUTHOR]