Flexible reproductive timing can buffer reproductive success of Pygoscelis spp. penguins in the Antarctic Peninsula region

Varying the timing of reproduction in response to local environmental conditions is a key factor influencing reproductive success. We used 19 yr (1991 to 2009) of data on breeding chronology and reproductive success of Adelie penguins Pygoscelis adeliae and gentoo penguins P. papua at King George Island, Antarctica to compare clutch initiation dates (CIDs), hatch rates, and creche rates at population and individual levels. The CIDs of both species occurred earlier with warmer October temperatures, but gentoo penguins adjusted CIDs twice as much per C of temperature as Adelie penguins. Gentoo penguins also exhibited lower variances in hatch and creche rates than Adelie penguins, suggesting that greater ability to respond to ambient conditions can buffer reproductive success. Mixed-effects models revealed that individual-and year-specific random effects on the overall population mean best accounted for observed variation in CIDs, with some individuals routinely breeding earlier than others. However, individual differences in the relative timing of breeding provided no advantage for long-term reproductive success. The results suggest that, among gentoo and Adelie penguins, plasticity in CIDs with respect to environmental conditions is primarily a population-level rather than an individual-level response. Energetic constraints of contrasting migratory and fasting behaviors likely contribute to the different abilities to respond to warming spring temperatures. Overall, larger responses of gentoo penguin CIDs to October temperature and lower variability in reproductive success, despite reduced reproductive success with delayed breeding, suggests that gentoo penguins are better equipped than Adelie penguins to adjust to rapid warming in the Antarctic Peninsula ecosystem.