Natal dispersal and philopatry in a group-living but noncooperative passerine bird, the vinous-throated parrotbill

Dispersal is a key factor affecting the dynamics and genetic structure of populations. Patterns of natal dispersal vary widely depending on the selection pressures that each species encounters, but the underlying factors determining this variation are poorly understood. We studied the pattern of natal dispersal in a small passerine, the vinous-throated parrotbill, Paradoxornis webbianus, using both direct ringing data and indirect genetic methods. The social structure of this species is characterized by group living without apparent territorial behaviour. The dispersal rate of juveniles from their natal groups was moderate (about 40%) and dispersal distance was short, most individuals moving to neighbouring flocks. Sibling groups that included both sexes usually dispersed or were philopatric together so that they were found in the same winter flock where pairing occurs. Thus, the avoidance of inbreeding or intrasexual competition among siblings appears not to affect natal dispersal in this species. Instead, our results suggest that the benefits of dispersing in groups and/or selection of kin structure within social groups via kin-selected reproductive benefits may promote the observed dispersal pattern: sibling associations without separation of the sexes. This behaviour may have important implications for the kin structure of populations and the evolution of sociality.