Data for Long-Distance Natal Dispersal Is Relatively Frequent and Correlated with Environmental Factors in a Widespread Raptor

Dispersal is a critical process influencing population dynamics, and long-distance dispersal (LDD) can be especially important for gene flow and adaptability. However, little is known about the mechanisms of LDD because of the challenges of studying large-scale movements. We studied correlates of natal LDD using North American bird banding data for American kestrels (Falco sparverius) from 1960-2015. We used Bayesian hierarchical and spatial models to investigate temporal trends and the effects of sex, migration strategy, weather, and agricultural landcover on LDD frequency and distance and account for sampling bias. Nearly half of all natal dispersal (48.7%) was LDD (classified as > 30 km), and the likelihood of LDD was positively associated with the proportion of agricultural landcover around natal sites. LDD distance was positively correlated with latitude, a proxy for migration strategy, indicating that migratory individuals disperse farther than residents. For male kestrels, LDD was positively associated with maximum summer temperature. Unlike previous studies of short-distance dispersal (SDD), we did not find sex-bias in dispersal distance or frequency. Sampling affected frequency and magnitude of LDD, likely because local studies more frequently capture short-distance dispersal within study areas. We suggest that LDD and SDD may be distinct processes rather than two outcomes originating from a single dispersal distribution. Long-distance dispersal and SDD have different ultimate effects, and the results presented here suggest that LDD frequency and distance are influenced by different proximate intrinsic and environmental factors compared to SDD.