Reproductive consequences of environment-driven variation in Adelie penguin breeding phenology

Adelie penguins Pygoscelis adeliae exhibit phenological variability across their geographic range due to fixed and variable forcing factors acting differentially on populations. Shifts in breeding phenology can be indicative of environmental change when cues for breeding initiation are tightly linked with environmental conditions. Adelie penguins on opposite sides of Antarctica display contrasting trends in clutch initiation dates, with different explanations of underlying causes. To make comparisons possible with a third significant Adelie penguin population region, we examined temporal trends and driving factors of breeding phenology at Bechervaise Island in East Antarctica. We have extended existing knowledge by examining how phenological dates are related throughout a breeding season, as well as the reproductive consequences of phenological variation. In contrast to other sites, we saw no evidence at this site of shifts towards early or delayed arrival or clutch initiation. Arrival, clutch initiation dates and the length of the incubation period had different environmental forcing factors, which explained up to 36% of the temporal variability. Penguins had a reduced courtship and egg-lay period when their arrival was delayed, and this led to later clutch initiation, later parent departure for foraging trips and later chick hatch. The phenological variations recorded here were not detrimental to chick-rearing. In particular, a delay in the start of breeding activities did not result in poor reproductive success. This indicates the importance of other factors for chick survival. Inter-annual phenological variability at this location is compared with that at other locations to further develop the colony latitude-breeding phenology relationship for Adelie penguins.