Local Recruitment and Natal Dispersal Distances of American Kestrels

Abstract

Variation in recruitment patterns and dispersal behavior can have important consequences for population viability, genetic structure, and rates of evolutionary change. From 1992 to 2006 we studied a marked population of American Kestrels (Falco sparverius) nesting in boxes in southwestern Idaho to identify factors that affect local recruitment and natal dispersal distances. A low proportion (4%) of locally produced kestrels (n = 2180) returned to nest in study area boxes. Offspring of locally produced individuals were 3.1 times more likely to return than offspring of parents that did not hatch in study area boxes and, independent of a parent's origin, males were 1.8 times more likely than females to return. Kestrels that hatched earlier in the breeding season and those that hatched immediately prior to a mild winter were more likely to return. Local natal dispersal distances were best explained by sex and parental origin but not by hatching dates. Fifty-four males moved an average of 5.3 km from their natal box to the location of their first breeding in the study area, and 27 females moved an average of 9.8 km. Offspring of locally produced parents dispersed shorter distances within the study area than offspring of other parents, and local natal dispersal distances of locally produced parents correlated with those of their same-sex offspring. Patterns of natal dispersal of American Kestrels in southwestern Idaho appear to be driven by a combination of parental dispersal tendencies and ecological factors. The population consists of a mix of immigrants and philopatric birds.