Correlates of Hunting Range Size in Breeding Merlins

Abstract

I studied variables affecting size of hunting range in breeding Merlins (Falco columbarius) from May to July, 1987-1990 in Saskatoon, Canada. Males were monitored during most of the breeding season, whereas females were observed only in the fledging period when they hunt. During the incubation period, the abundance of total prey birds (<100 g) and House Sparrows (Passer domesticus, the primary prey) was negatively correlated with hunting range size of males whereas in the nestling period, only total bird abundance was negatively correlated with the hunting range size. Most males changed their range sizes from the incubation to nestling period inversely with changes in prey abundance on their ranges. For females, both body mass and House Sparrow abundance were negatively correlated with hunting range size. I found no significant effect of clutch/brood size and intruder density on hunting range size of Merlins. Similarly, no clear seasonal pattern emerged in the size of hunting ranges of males.