Stable isotopes document the winter foraging ecology of king penguins and highlight connectivity between subantarctic and Antarctic ecosystems

Abstract

The poorly known winter foraging ecology of the king penguin, a major Southern Ocean consumer, was investigated at the subantarctic Crozet Islands where the largest global population breeds. Blood δ13C and δ15N values were used as proxies of the birds’ foraging habitat and diet, respectively, and circulating prolactin levels helped in determining the birds’ reproductive status. Plasma prolactin concentrations showed that king penguin adults of unknown breeding status (n = 52) that were present at the colony in winter were in fact breeders and failed breeders, but were not non ‐breeders. Circulating prolactin was neither related to δ13C nor δ15N values, thus suggesting that both breeders and failed breeders used the same foraging habitats and fed on the same prey. Plasma and blood cell isotopic values depicted four new relevant biological features on the feeding strategies of king penguins during the critical winter period: (1) 42% of the birds foraged in the distant Antarctic Zone, but 58% fed primarily in subantarctic waters (δ13C), (2) they preyed upon myctophids in both zones (δ15N), (3) individuals were consistent in their foraging strategies over the winter months (δ13C and δ15N), and (4) a higher proportion of females (77%–80%) than males (27%–31%) favored feeding in distant Antarctic waters (δ13C). This study highlights trophic connectivity between subantarctic and Antarctic ecosystems and hence the key role of energy export from Antarctic waters to sustain breeding populations of subantarctic predators, including during the Austral winter.

Exploration during early life: distribution, habitat and orientation preferences in juvenile king penguins

“…6). Previously, both breeders and failed-breeders from the Crozet islands have also been reported to forage within the AZ during winter [65, 66], and within the SAF [66].…”

Sea-ice edge is more important than closer open water access for foraging Adélie penguins: evidence from two colonies

“…They also were only slightly lower than the isotopic ratio of Adélie penguin chicks of 10.2 ± 0.8‰ (whole blood analysis; Cherel 2008). Our samples consisted of delipidated plasma, for which δ 15 N values are about 0.8‰ higher than in the red blood cells (but not δ 13 C), as shown in king Aptenodytes patagonicus and gentoo penguins Pygoscelis papua (Xavier et al 2017, Cherel et al 2018. With this in mind, the difference in δ 15 N values between krill and Adélie penguins in our results corresponds to the natural enrichment factor of about 3.4‰ between trophic levels (Post 2002), suggesting that these penguins were feeding principally on Antarctic krill, with males probably feeding on a small proportion of Antarctic silverfish and ice krill leading to an increase in their δ 15 N values.…”

Decades of dietary data demonstrate regional food web structures in the Southern Ocean

“…Understanding the structure and function of food webs during the winter remains one of the largest gaps in Southern Ocean ecosystems research. Increasing amounts of data are becoming available on the winter activity and diet of some predator species (Cherel et al., 1996) with new techniques such as stable isotopes, fatty acids, and DNA also beginning to provide further insight into predator–prey dynamics in the Southern Ocean (Cherel et al., 2018). Such techniques help fill gaps that result from the limitations of stomach content data.…”