Short-toed snake eagles Circaetus gallicus (Gmelin, 1788) (Aves: Accipitridae) approaching a water barrier show reverse direction of migration

Abstract

We investigated the directions of migration (reversed vs. expected) of raptors approaching a geographical strait in relation to local wind conditions, time of day, flock size and location of the observation post (coastal zone vs. inland zone). Fieldwork was conducted during autumn migration in 2011, 2012 and 2013 at a migratory bottleneck located in the southernmost part of the Italian Peninsula (Calabrian Apennines), using four watch points. In this area, migrating birds face the narrowest water surface between continental Italy and Sicily, the Strait of Messina. The only species showing substantial reverse migration was the short-toed snake eagle (Circaetus gallicus). In particular, eagles, mostly first calendar year (cy) birds, showed this behavior when passing closer to the coast (5 km inland of the Strait of Messina). Our results could reflect the reluctance of these birds to head south when approaching this relatively short stretch of sea, even before reaching the coastline. This behavior could be evidence of the strong selective pressure, which would have led to the evolution of the extremely detoured flight path of birds breeding in Italy.