A comprehensive review of the phenology of <Emphasis Type="Italic">Pygoscelis</Emphasis> penguins

Phenology, the study of stages within the life cycles of plants and animals, has served as a proxy for weather and climate throughout human history, but has only recently become its own field of environmental science. Phenological constraints are particularly demanding in avian species because of the necessity of matching chick provisioning with high food abundance, while allocating time for migration. Within avian species, seabird phenology is of particular interest because many seabird species exhibit colonial breeding behaviour. Penguins, representing roughly 90 % of the biomass in the Southern Ocean, are well studied in the context of population dynamics, prey abundance, and phenology. Here I review the annual cycles of Pygoscelis penguins, a genus including gentoo (Pygoscelis papua), chinstrap (Pygoscelis antarctica), and Adélie (Pygoscelis adeliae) penguins, to better understand what is known about their phenology, what causes known changes, and how their phenology influences fitness. Major differences exist between species, particularly in relation to winter migration, incubation shifts, and the timing of breeding. Even with the numerous studies examining phenology in Pygoscelis penguins, large gaps in our understanding of plasticity in the annual cycle remain. In particular, certain phases are neglected because they are logistically difficult to record or have erroneously been ignored. In addition, temporally, large gaps exist in our understanding of phenology, where studies have not been updated in over 20 years at a particular field site. Because phenology does vary greatly between years, depending on the colony, when possible, researchers should strive to update phenological records by recording the dates of phases each year.