Faster growth and larger size at creche onset are associated with higher offspring survival in Adelie Penguins

We conducted the first assessment of Adelie Penguin (Pygoscelis adeliae) chick survival that accounts for imperfect resighting. We found that when chicks are larger in size when they enter the creche stage (the period when both parents forage at the same time and chicks are left relatively unprotected), they have a higher probability of survival to fledging. We investigated the relationships between growth, creche timing, and chick survival during one typical year and one year of reduced food availability. Chicks that hatched earlier in the season entered the creche stage older, and chicks that both grew faster and creched older entered the creche at a larger size. These relationships were stronger in the year of reduced food availability. Thus, parents increased their chicks' chance of fledging if they provided sufficient food for faster growth rates and/or extended the length of the brood-guarding period. Early nest initiation (i.e., early hatching) provided parents with the opportunity to extend the guard period and increase chick survival. However, to extend the guard stage successfully, they must provide larger meals and maintain higher chick growth rates, even if just one parent at a time is foraging, which previous work has shown is not possible for all individuals. We show that the factors governing tradeoffs in chick-rearing behavior of Adelie Penguin parents may vary in accord with environmental conditions, a result from which we can better understand species' adaptations to environmental changes. Lay Summary center dot When raising dependent young, animals must balance how much to invest in guarding the brood versus finding food for them. These so-called tradeoffs can influence how well the current brood grows and survives to independence. center dot During two breeding seasons, one typical and one apparently food limited, we related Adelie Penguin chick survival rates to how fast they grew and the timing of a critical transition in brood-rearing when chicks switch from being guarded continuously by a parent to being left alone while both parents forage at the same time. center dot We found that with a combination of early hatching and fast-growing, chicks entered the unguarded ("creche") stage older and larger and, therefore, had a better chance of surviving to independence. center dot Certain parents can manage tradeoffs to maximize breeding success even during unfavorable conditions. These results can help us understand how populations will respond to changing climate and habitats.