Understanding the factors driving phenotypic and genomic differentiation of insular populations is of major interest to gain insight into the speciation process. Comparing patterns across different insular taxa subjected to similar selective pressures upon colonizing oceanic islands provides the opportunity to study parallel evolution and identify shared patterns in their genomic landscapes of differentiation. We selected four species of passerine birds (common chaffinch Fringilla coelebs/canariensis, red-billed chough Pyrrhocorax pyrrhocorax, house finch Haemorhous mexicanus and dark-eyed/island junco Junco hyemalis/insularis) that have both mainland and insular populations. For each species, we sequenced whole genomes from mainland and insular individuals to infer their demographic history, characterize their genomic differentiation, and identify the factors shaping them. We estimated the relative (FST) and absolute (dxy) differentiation, nucleotide diversity (π), Tajima’s D, gene density and recombination rate. We also searched for selective sweeps and chromosomal inversions along the genome. Changes in body size between island and mainland were consistent with the island rule. All species shared a marked reduction in effective population size (Ne) upon island colonization. We found highly differentiated genomic regions in all four species, suggesting the role of selection in island-mainland differentiation, yet the lack of congruence in the location of these regions indicates that each species adapted to insular environments differently. Our results suggest that the genomic mechanisms involved, which include selective sweeps, chromosomal inversions, and historical factors like recurrent selection, differ in each species despite the highly conserved structure of avian genomes and the similar selective factors involved.

Quantifying space use and segregation, as well as the extrinsic and intrinsic factors affecting them, is crucial to increase our knowledge of species-specific movement ecology and to design effective management and conservation measures. This is particularly relevant in the case of species that are highly mobile and dependent on sparse and unpredictable trophic resources, such as vultures. Here, we used the GPS-tagged data of 127 adult Griffon Vultures Gyps fulvus captured at five different breeding regions in Spain to describe the movement patterns (home-range size and fidelity, and monthly cumulative distance). We also examined how individual sex, season and breeding region determined the cumulative distance travelled and the size and overlap between consecutive monthly home-ranges. Overall, Griffon Vultures exhibited very large annual home-range sizes of 5,027 ± 2,123 km2, mean monthly cumulative distances of 1,776 ± 1,497 km, and showed a monthly home-range fidelity of 67.8 ± 25.5 %. However, individuals from northern breeding regions showed smaller home-ranges and travelled shorter monthly distances than those from southern ones. In all cases, home-ranges were larger in spring and summer than in winter and autumn. Moreover, females showed larger home-ranges and less monthly fidelity than males, indicating that the latter tended to use the similar areas throughout the year. Overall, our results indicate that both extrinsic and intrinsic factors modulate the home-range the social Griffon Vulture and that spatial segregation depend on sex and season at the individual level, without relevant differences between breeding regions in individual site fidelity.