Determinants of Dispersal in Breeding Merlins (Falco Columbarius)

Abstract

Determinants of adult dispersal were studied in a population of color—banded Merlins (Falco columbarius). In the analysis, I examined the effects of local population density, breeding performance, survival, and characteristics of the mate on movements between breeding seasons. The distance moved between successive breeding seasons varied greatly, both between and within individuals. Fidelity to the breeding areas was higher in males than females, and females dispersed nearly three times as far as males did. Males breeding at high density dispersed shorter distances than other males. Dispersal distances of females were related to aspects of the mate. Females that mated with older males, and with males that survived to the next season, made shorter movements than other females. In both sexes, low reproductive success was associated with long dispersal distances in the next year. Moreover, nest predation in one season resulted in lower return rate by females, but not males. Hence, breeding Merlins responded to their social as well as natural environment by dispersing from areas associated with low survival and poor reproductive performance.