relationship between brood size and prey selection in a Peregrine Falcon population located in a strategic region on the Western European Flyway

In raptors, brood size seems to be closely related to the size of prey brought to the nest, the delivery rate and the degree of parental effort. In the case of Peregrine Falcons (Falco peregrinus), any increase in the size of prey is considered to be linked to the increased role of the female in hunting. We investigated the possible effects of differences between sexes in prey composition on the brood size of a Peregrine Falcon population in northern Spain during 1998–2010. The study area was located on the Gulf of Biscay, in the middle of the Western European Flyway, hence a wide range of prey species were available during the breeding season. We monitored a total of 320 Peregrine nests, which produced 603 fledglings (average brood size = 2.67) and identified 2,832 prey, from 128 different bird species. Our results indicate that brood size was negatively related to bad weather (e.g. rainfall in April), but not with the body mass of the prey species delivered to the nest. There were no significant differences in body mass between attacked versus captured prey, nor was mass affected by the sex of the attacking Peregrine, and gender had no significant effect on the probability of a successful capture. Therefore, males and females hunted prey species of similar body size. Our data suggest that prey size is not related to the number of fledglings, although this may play an important role; Peregrines can compensate by hunting for more or larger prey.