Data from: The price of associating with breeders in the cooperatively breeding chestnut-crowned babbler: foraging constraints, survival and sociality

Understanding the costs of living with breeders might offer new insights
into the factors that counter evolutionary transitions from selfish
individuals to cooperative societies. While selection on early dispersal
is well-understood, it is less clear whether costs are also associated
with remaining with family members during subsequent breeding; a
pre-requisite to the evolution of kin-based cooperation. We propose and
test the hypothesis that living in groups containing breeders is costly
and that such costs are exacerbated by increasing group size. For example,
in group-living central-place foragers, group members might suffer from
resource depletion when foraging in a restricted area during breeding and
significant costs of repeatedly travelling between foraging patches and
the site of offspring. Using the cooperatively breeding chestnut-crowned
babbler (Pomatostomus ruficeps), for which grouping during breeding is
obligatory, we show that reproduction is associated with substantially
reduced foraging areas and evidence of resource depletion, particularly in
larger groups. Such effects largely persisted from the onset of incubation
through to offspring independence 4-5 months later. All group members,
irrespective of their breeder or helper status, lost significant body mass
over this period, and, in males, mass loss was associated with reduced
inter-annual survival. Although babblers are constrained from living
outside of breeding groups due to high risks of predation and the poor
success of breeding without helpers, we suggest that the effects we
describe may generally select against group-living during breeding
attempts in species where constraints to independent breeding and costs of
dispersal are less acute.