Comparison of Gyrfalcon Distributions Between the Palearctic and Nearctic.

Abstract

—The Gyrfalcon (Falco rusticolus) is a circumpolar arctic raptor, using tree nests of other birds or cliff ledges for nesting. Its breeding distribution coincides with the distributions of its main prey, Rock Ptarmigan (Lagopus muta) and Willow Ptarmigan (L. lagopus). In the Palearctic, the range of the Gyrfalcon is relatively well studied except for the area between the Ob River and the Taimyr Peninsula in Russia. Uncertainty also existed for the Kamchatka Peninsula, which was regarded as a “possible, but yet proven” area for nesting until 2007 when Lobkov, with coauthors, published their data about nesting Gyrfalcons on the whole peninsula. Breeding Gyrfalcons in the Palearctic are mainly restricted to the forest-tundra zone and coastal rock cliffs, and they rely more often on tree nests than cliff nests, which is almost the reverse picture of the Nearctic, where Gyrfalcons are able to nest further north than Peregrines (Falco peregrinus), their direct competitors. The range overlap between these two top-predators is very small (ca. 10%) in the Palearctic compared to the Nearctic, where overlap can be up to 30%. We explore the reasons for that contrast, pointing out that overlap occurs mostly in areas where the two species of ptarmigan coexist (at the limit of the tree line, for example). In the context of climate change, with southern species predicted to move northward, it is still difficult to predict the outcome of potential increasing competition with Peregrines, considering that the Willow Ptarmigan is well known as a very flexible species under various climatic conditions. In Russia, perhaps the most pressing conservation issue is not the possible climatic impacts, but a heavy pressure of poaching of both adult and nestling Gyrfalcons, which has the potential to limit the population of this key predator. Received 9 September 2011, accepted 21 September 2011. POKROVSKY, I., AND N. LECOMTE. 2011. Comparison of Gyrfalcon distributions between the Palearctic and Nearctic. In R. T. Watson, T. J. Cade, M. Fuller, G. Hunt, and E. Potapov (Eds.). Gyrfalcons and Ptarmigan in a Changing World. The Peregrine Fund, Boise, Idaho, USA. http://dx.doi.org/10.4080/gpcw.2011.0107