Influence of phenotypic and social traits on dispersal in a family living, tropical bird

Individual variation in natal dispersal behaviors has extensive ecological and evolutionary consequences. Traits such as offspring sex, age, and body condition may influence dispersal, resulting in a potentially complex suite of associations in traits that can affect fitness. Conceivably, individuals with particular phenotypes may breed in different habitats, thus potentiating the development of geographic variation. Moreover, studies typically underestimate dispersal distance owing to sampling issues and rarely consider the direction of movement, limiting understanding of this important life history stage. I examined the influence of phenotypic and social traits on dispersal distance and direction in a family living bird, the western slaty antshrike (Thamnophilus atrinucha). When accounting for detection probability, juveniles dispersed 114 territories and 461268 m. The age at dispersal and body mass upon leaving the nest influenced dispersal distance and direction. Older and heavier individuals dispersed shorter distances. Younger individuals dispersed towards comparatively younger forest with a higher density of antshrike territories. Older and heavier offspring may be more competitive and/or have increased experience with the local habitat, increasing their probability of acquiring nearby territories. Contrary to other studies, sex-biased dispersal distance was not observed. Instead, the sexes dispersed in different directions, potentially to reduce the risk of inbreeding. This study revealed the importance of age at dispersal and body mass on variation in dispersal behaviors and highlighted the need to investigate sex biases in dispersal direction.