Data from: Sex roles, parental care and offspring growth in two contrasting coucal species

The decision to provide parental care is often associated with trade-offs,
because resources allocated to parental care typically cannot be invested
in self-maintenance or mating. In most animals, females provide more
parental care than males, but the reason for this pattern is still debated
in evolutionary ecology. To better understand sex differences in parental
care and its consequences we need to study closely related species where
the sexes differ in offspring care. We investigated parental care in
relation to offspring growth in two closely related coucal species that
fundamentally differ in sex roles and parental care, but live in the same
food-rich habitat with a benign climate, and have a similar breeding
phenology. Incubation patterns differed and uniparental male black coucals
fed their offspring two times more often than female and male white-browed
coucals combined. Also, white-browed coucals had more `off-times´ than
male black coucals, during which they perched and preened. However, these
differences in parental care were not reflected in offspring growth,
likely because white-browed coucals fed their nestlings a larger
proportion of frogs than insects. A food-rich habitat with a benign
climate may be a necessary, but – perhaps unsurprisingly – is not a
sufficient factor for the evolution of uniparental care. In combination
with previous results (Goymann et al. (2015) J. Evol. Biol. 28, 1335-1353)
these data suggest that white-browed coucals may cooperate in parental
care because they lack opportunities to become polygamous rather than
because both parents were needed to successfully raise all offspring. Our
case study supports recent theory suggesting that permissive environmental
conditions in combination with a particular life-history may induce sexual
selection in females. A positive feed-back loop between sexual selection,
body size, and adult sex-ratio may then stabilize reversed sex-roles in
competition and parental care.