Spatial and isotopic niche partitioning during winter in chinstrap and Adélie penguins from the South Shetland Islands

Abstract

Abstract. Closely related species with similar ecological requirements should exhibit segregation along spatial, temporal, or trophic niche axes to limit the degree of competitive overlap. For migratory marine organisms like seabirds, assessing such overlap during the non-breeding period is difficult because of longdistance dispersal to potentially diffuse foraging habitats. Miniaturization of geolocation devices and advances in stable isotope analysis (SIA), however, provide a robust toolset to quantitatively track the movements and foraging niches of wide ranging marine animals throughout much of their annual cycle. We used light-based geolocation tags and analyzed stable carbon and nitrogen isotopes from tail feathers to simultaneously characterize winter movements, habitat utilization, and overlap of spatial and isotopic niches of migratory chinstrap (Pygoscelis antarctica) and Adélie (P. adeliae) penguins during the austral winter of 2012. Chinstrap penguins exhibited a higher diversity of movements and occupied portions of the Southern Ocean from 1388 W to 308 W within a narrow latitudinal band centered on 608 S. In contrast, all tracked Adélie penguins exhibited smaller-scale movements into the Weddell Sea and then generally along a counter-clockwise path as winter advanced. Inter-specific overlap during the non-breeding season was low except during the months immediately adjacent to the summer breeding season. Intra-specific overlap by chinstraps from adjacent breeding colonies was higher throughout the winter. Spatial segregation appears to be the primary mechanism to maintain inter-and intra-specific niche separation during the nonbreeding season for chinstrap and Adélie penguins. Despite low spatial overlap, however, the data do suggest that a narrow pelagic corridor in the southern Scotia Sea hosted both chinstrap and Adélie penguins for most months of the year. Shared occupancy and similar isotopic signatures of the penguins in that region suggests that the potential for inter-specific competition persists during the winter months. Finally, we note that SIA was able to discriminate eastward versus westward migrations in penguins, suggesting that SIA of tail feathers may provide useful information on population-level distribution patterns for future studies.

Seasonal consistency and individual variation in foraging strategies differ among and within Pygoscelis penguin species in the Antarctic Peninsula region

“…These results also agree with tracking studies indicating that Adélie and chinstrap penguins disperse broadly during the post-breeding period while gentoo penguins remain close to their breeding colonies and forage in open-water, near-shore habitats (Wilson 2010;Hinke et al 2015).…”

“…Therefore, whole blood samples provide a proxy for dietary information during the incubation period of the 2010 breeding season at Admiralty Bay and the 2014 breeding season at Wiencke, Rongé, and Elephant Islands. Molt in the three penguin species occurs immediately after the breeding season (i.e., late February through March; Hinke et al 2015) and feathers are metabolically inert after synthesis (Hobson and Clark 1992). As such, body feathers collected for this study reflect trophic level and foraging areas visited during the pre-molt period in the post-breeding stages after the 2009 breeding season at Admiralty Bay and 2013 breeding season at Wiencke, Rongé, and Elephant Islands, respectively.…”

Overwinter habitat selection by Antarctic krill under varying sea-ice conditions: implications for top predators and fishery management

“…Comparatively less monitoring of predator populations has occurred during postbreeding periods, especially in winter. Many species that are monitored within the CEMP undergo latesummer migrations to overwinter in other areas of the Antarctic or sub-Antarctic (Stevick et al 2004, Lea et al 2008, Hinke et al 2015. It was assumed that spatial overlap and negative interactions between these krill predators and the fishery were minimal during winter in the Antarctic Peninsula.…”

Stable isotope analyses of feather amino acids identify penguin migration strategies at ocean basin scales

“…While the spatial resolution of essential AA δ 13 C is coarse compared to direct tracking, this modified from Hinke et al [10]. Dotted lines represent 50% probability of assignment.…”