When approached by predators, prey must decide whether to flee or remain and fight. The economics of such decisions are underlain by the trade-off between current and residual fitness. The trade-off predicts that (i) breeders should be less prone than non-breeders to flee from approaching predators, as breeders can lose their investment into current reproduction
(ii) among breeders, parents should increasingly defend their offspring with increasing investment into the brood (brood value hypothesis), at least until the offspring can independently take part in anti-predator defenses
and (iii) for a similar investment into reproduction, breeders with lower perspectives to fledge or wean their young should invest less into offspring defense. We tested these predictions in a colonially breeding seabird, the king penguin (Aptenodytes patagonicus). Specifically, we considered how antipredator behaviors varied according to life history stage (molting, courting, breeding), offspring age and their dependence on parents for antipredator defenses, and the timing of breeding, with late breeders being very unlikely to fledge offspring in this species. Using non-lethal human approaches to mimic the threat of predation, we approached >
500 penguins and measured their alert and flight initiation distances, as well as the distance fled. We found that birds showed increasingly stronger antipredator behaviors as they initiated and increased their investment into reproduction, from non-reproductive stages to courting and brooding small, thermo-dependent chicks. However, once offspring gained thermal independence and freedom of movement, parents reduced their antipredator behaviors. Late breeders were more likely to flee from the approaching threat than early breeders. Altogether, our results demonstrate that parental antipredator responses are dynamic and shaped by the levels of investment into current reproduction, the ability of offspring to defend themselves, and the perceived future value of the brood.