Structural size measurements and isotopic signatures of foraging among adult male and female Adélie penguins (Pygoscelis adeliae) nesting along the Palmer Archipelago near Palmer Station, 2007-2009

Sexual segregation in vertebrate foraging niche is often associated with sexual size
dimorphism (SSD), i.e., ecological sexual dimorphism. We examined ecological sexual dimorphism
among sympatric nesting Pygoscelis penguins near Palmer Station, Antarctica, asking whether
environmental variability in the form of winter sea ice is associated with differences in male
and female pre-breeding foraging niche. Each season, study nests, where pairs of adults were
present, were individually marked and chosen before the onset of egg-laying, and consistently
monitored. When study nests were found at the one-egg stage, both adults were captured to
obtain blood samples used for molecular sexing and stable isotope analyses, and measurements
of structural size and body mass. At the time of capture, each adult penguin was quickly blood
sampled (~1 ml) from the brachial vein. After handling, individuals at study nests were
further monitored to ensure the pair reached clutch completion, i.e., two eggs. Molecular
analyses were conducted at Simon Fraser University following standard PCR protocols, and
stable isotope analyses were conducted at the Stable Isotope Facility at the University of
California, Davis using an elemental analyzer interfaced with an isotope ratio mass
spectrometer