Data and code from: Density and kinship interactively affect natal dispersal in a social bird

Dispersal in animals is influenced by diverse environmental cues, among
which population density and kinship are key drivers. High density can
promote dispersal by intensifying intraspecific competition or inhibit it
through group-living advantages. Likewise, kin interaction may enhance
dispersal via kin competition or limit it through kin-selected fitness
gains. However, the interplay between them remains inadequately
elucidated. We investigated how density and kinship interacted to
influence natal dispersal in silver-throated tits (Aegithalos
glaucogularis), a social species showing facultative cooperative breeding
during the breeding season and group-living thereafter. We found
female-biased natal dispersal, consistent with male-biased helping
behaviour. For males, the natal dispersal distance was negatively
associated with the number of male siblings fledging from the same nest,
and this relationship intensified with increasing fledgling density around
the natal nest, indicating that density can modulate kin selection’s
constraining effect on dispersal. Furthermore, with increasing male
sibling number, fledgling density’s effect on male dispersal distance
shifted from positive to negative, suggesting that potential kin selection
opportunity can reverse the direction of the density effect. These
findings demonstrate that density and kin selection opportunities interact
to shape dispersal dynamics, offering new insights into their combined
roles in driving the evolution of dispersal strategies.