Spatial patterns of territorial large falcons influence mixed pair formation in an arid environment

Interspecific crossbreeding among breeding populations can lead to outbreeding depression and reduce individual fitness. Mixed pairs occur more frequently in areas with fragmented habitat where individual species often have low population densities. Due to the genetic affinities among falcons, hybrids from within this group exhibit full or partial fertility, presumably over indefinite generations. This study aims to ascertain the influence of spatial patterns of territory holders (pairs and non-paired individuals) on the occurrence of mixed pairs among large falcons (Barbary Falco peregrinus pelegrinoides and Lanner Falcons F. biarmicus tanypterus) in Saudi Arabia. We found that mixed pairs occurred in study areas (5.4% of territories) with higher nearest neighbour distances (NND). Densities per se had no effect on the occurrence of mixed pairs, and neither did the quality of territories. Favourable but restricted core areas maintain a healthy breeding population but separated by very large unfavourable terrains. Distances from core areas affect the presence of pairs and unpaired falcons. Higher distances (>200 km) force potential breeders to mate and breed interspecifically. Probably a modest risk of outbreeding depression occurred, but the desirable re-establishment of gene flow between population fragments, also using reintroduction techniques will minimize the risk by decreasing the chance for the occurrence of mixed pairs.