Motion capacity, geography and ecological features explain the present distribution of a migratory top predator

Abstract

Presence and distribution of ecological barriers shapes the distribution of migratory birds as well as any other living organism. In Italy, short-toed snake eagles (Circaetus gallicus) breed in the northern and western areas of the peninsula but the species is rare in the south or the islands. The Italian population of this species migrates across the Mediterranean at the Strait of Gibraltar rather than crossing the large stretch of sea between Sicily and Tunisia. This suggests that, in Italy, fall migration is oriented south-north and spring migration north-south. In this paper we test the hypothesis that the accessibility of the suitable habitat area along the Italian Peninsula is in relation to the geographical migration pattern of the studied species. We integrated information from the movement ecology, the geography and the traditional ecological features in order to provide an ecological explanation of the current biogeographical pattern of our model species. We compared statistical models with and without latitude as a predictor. Each model was based on ecological and geographical variables, including land use, prey availability, spatial distribution of environmental elements (patch analysis), geomorphology, and geography. These models predict two patterns of suitability for short-toed snake eagles in Italy. Our results suggest that the abundance of this species increases with latitude despite the existence of large areas of suitable habitat in southern Italy. We suggest that the actual distribution of the short-toed snake eagle in Italy is influenced by the particular migration path used by this population, supporting the hypothesis that this species is still colonizing the Italian Peninsula through an unexpected colonization direction from north to south.

Sea crossing as a major determinant for the evolution of migratory strategies in soaring birds

“…This comparison among the three species highlights how the response to a major obstacle like the sea crossing is species‐specific and depends mainly upon wing morphology (Agostini, Panuccio, & Pasquaretta, 2015). Such differences in motion capacity have profound effects also on the colonization patterns of these raptors: while the osprey is virtually cosmopolitan, the short‐toed eagle is absent from large Mediterranean islands, perhaps because its colonization pathways are much more constrained by the distribution of land masses (Panuccio, Lucia, Agostini, Ottonello, & Bogliani, 2015).…”

Individual variation in orientation promotes a 3000‐km latitudinal change in wintering grounds in a long‐distance migratory raptor

“…, Agostini & Mellone , Panuccio et al . , ). Interestingly, however, observations carried out in Marettimo Island, between Sicily and Tunisia, also showed the existence of another migratory pathway, comprising almost exclusively juveniles (Agostini et al .…”

“…, Panuccio et al . , ). In this paper, we present data for five additional satellite‐tracked juveniles, which included birds that followed the more direct southerly route.…”

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

“…As a result, we focused the analysis on this species. Since this eagle does not breed in the study area (Panuccio et al 2015), our observations involved migrating birds. The median date of the passage of this species was on 26 September, and among aged eagles (N = 40) 33 (82.5%) were first calendar year (cy) birds.…”