Isotopic niches of emperor and Adelie penguins in Adelie Land, Antarctica

The emperor and Adelie penguins are the only two species of penguins that co-occur at high-Antarctic latitudes. We first measured and compared their isotopic niches on the same year in Adelie Land in spring, when the two species co-exist. Emperor and Adelie penguins segregated by their blood isotopic signatures, with adult delta(13)C values (-24.5 +/- 0.2 and -25.4 +/- 0.2 parts per thousand, respectively) suggesting that emperor penguins foraged in more neritic waters than Adelie penguins in spring. At that time, difference in their delta(15)N values (4.1 parts per thousand, 12.0 +/- 0.4 vs. 7.9 +/- 0.1 parts per thousand) encompassed more than one trophic level, indicating that emperor penguins preyed mainly upon fish (and squids), while Adelie penguins fed exclusively on euphausiids. Second, we compared the food of breeding adults and chicks. The isotopic signatures of adults and chicks of emperor penguins were not statistically different, but delta(15)N value of Adelie penguin chicks was higher than that of adults (10.2 +/- 0.8 vs. 9.0 +/- 0.2 parts per thousand). The difference showed that adult Adelie penguins captured higher trophic level prey, i.e. higher-quality food, for their chicks. Third, the isotopic signatures of Adelie penguins breeding in Adelie Land showed that adults fed on Antarctic krill in oceanic waters in spring and shifted to neritic waters in summer where they preyed upon ice krill for themselves and upon fish and euphausiids for their chicks. A comparison of isotopic niches revealed large overlaps in both blood delta(13)C and delta(15)N values within the community of Antarctic seabirds and pinnipeds. The continuum in delta(15)N values nevertheless encompassed more than one trophic level (5.2 parts per thousand) from Adelie penguin and crabeater seal to the Weddell seal. Such a broad continuum emphasizes the fact that all Antarctic seabirds and marine mammals feed on varying proportions of a few crustacean (euphausiids) and fish (Antarctic silverfish) species that dominate the intermediate trophic levels of the pelagic neritic and oceanic ecosystems.