Limited dispersal by large juvenile males leads to kin-structured neighborhoods in the black-crested titmouse (Baeolophus atricristatus)

Abstract

Dispersal of young from natal home ranges can result in gene flow and increased variation within populations. However, juveniles that remain near kin and form familial groups can accrue indirect fitness benefits. Between 2013 and 2015, we studied families (n = 34) of black-crested titmice (Baeolophus atricristatus) in central Texas to assess factors affecting juvenile dispersal. Our results suggest that males of greater mass relative to siblings tended to be more philopatric than smaller males or females of any size. Dispersal of juveniles was not affected by home range size of the territorial male, habitat composition of the home range (percent woodland cover), or date in which young fledged the nest. Interactions between neighboring groups of related titmice were more tolerant than interactions between unrelated groups. In most cases, retained male juveniles established territories adjacent to their natal home range, likely increasing their fitness by saving energy through tolerant interactions with kin. Certain species form family groups that provide additional fitness benefits to related individuals. However, not all kin-structured organisms respond to the same factors that enable the persistence of family-dominated populations. We examined factors that could influence the limited dispersal behavior of the black-crested titmouse, Baeolophus atricristatus, in central Texas. Limited dispersal occurs when a juvenile disperses a short distance (< 400 m) and establishes a territory adjacent to its natal home range the following year. In the black-crested titmouse, sex and mass of juveniles greatly influence limiting dispersing individuals, typically with the heaviest male juveniles exhibiting philopatry. Thus, overtime, kin-structured neighborhoods develop, allowing related family groups to spare energetically taxing aggressive behaviors and instead forage passively near one another.