Data from: Interplay of cooperative breeding and predation risk on egg allocation and reproductive output

Predation risk can influence behaviour, reproductive investment and,
ultimately, individuals’ fitness. In high-risk environments, females often
reduce allocation to reproduction, which can affect offspring phenotype
and breeding success. In cooperative breeders, helpers contribute to feed
the offspring, and groups often live and forage together. Helpers can
therefore improve reproductive success, but also influence breeders’
condition, stress levels and predation risk. Yet, whether helper presence
can buffer the effects of predation risk on maternal reproductive
allocation remains unstudied. Here, we used the cooperatively breeding
sociable weaver Philetairus socius to test interactive effects of
predation risk and breeding group size on maternal allocation to clutch
size, egg mass, yolk mass, and yolk corticosterone. We increased perceived
predation risk before egg laying using playbacks of the adults’ main
predator, gabar goshawk (Micronisus gabar). We also tested interactive
effects of group size and prenatal predator-playbacks on offspring
hatching and fledging probability. Predator-exposed females laid eggs with
4% lighter yolks, but predator-calls’ exposure did not clearly affect
clutch size, egg mass or egg corticosterone levels. Playback-treatment
effects on yolk mass were independent of group size, suggesting that
helpers’ presence did not mitigate predation risk effects on maternal
allocation. Although predator-induced reductions in yolk mass may decrease
nutrients’ availability to offspring, potentially affecting their
survival, playback-treatment effects on hatching and fledging success were
not evident. The interplay between helper presence and predator effects on
maternal reproductive investment is still an overlooked area of life
history and physiological evolutionary trade-offs that requires further
studies.