Do penguins share? Evidence of foraging niche segregation between but not within two sympatric, central-place foragers

Abstract

Niche theory predicts that sympatric species should differentiate ecologically in order to co-exist and conspecifics will also differentiate to reduce intra-specific competition. As central-place foragers, colonial breeding seabirds represent an ideal model system to test this theory and examine the mechanism of niche segregation. We used GPS-TDlog devices for tracking and diving data and stable isotope analysis to examine patterns of inter- and intra-specific niche segregation among southern rockhopper penguins Eudyptes chrysocome chrysocome and Magellanic penguins Spheniscus magellanicus breeding on Isla de los Estados, Argentina, across 3 consecutive breeding seasons. Tracking data indicated strong inter-specific spatial segregation of foraging locations and little overlap. Diving data also highlighted vertical foraging niche segregation as female rockhopper penguins dove deeper than male and female Magellanic penguins. δ13C values supported the general pattern of habitat segregation, with lower values for female rock-hopper penguins that dove deeper and foraged off the shelf break. Female rockhopper penguins exhibited a lower relative trophic value (δ15N) than male and female Magellanic penguins, consistent with previous dietary studies of both species. These differences likely act to reduce competition between the 2 species during the breeding season, when they are constrained to exploit the resources around their colonies. In contrast, male and female Magellanic penguins shared a similar foraging niche as measured by areas used to forage, dive depths, relative habitat use and trophic values. The lack of sex-specific foraging niche segregation of Magellanic penguins at Isla de los Estados could be related to the availability of food in the area and/or the small population size.