Fig 1.
The study sites are located along the cost of Northern Victoria Land, Antarctica. Sampling sites are marked with colored circles (red: Cape Hallett; blue: Cape Washington; green: Cape Möbius; and yellow: Inexpressible Island), and breeding sites of potential prey species of the South Polar Skua are indicated with triangles. This map was generated by the authors using publicly available map data (coastlines and breeding sites of prey) from the Korea Polar Research Institute (www.kopri.re.kr). The figure was prepared in Microsoft PowerPoint and is published under a CC BY 4.0 license.
Table 1.
Stable isotope values (δ13C and δ15N (mean ± SD)) of potential food sources at four sites in the Ross Sea region: Cape Hallett (CH), Cape Washington (CW), Cape Möbius (CM), and Inexpressible Island (II). Presence and absence of the species at each site are denoted by “O” and “X,” respectively.
Fig 2.
Stable isotope values in whole blood samples of South Polar Skuas at each site (CH: Cape Hallett; CW: Cape Washington; CM: Cape Möbius; and II: Inexpressible Island).
Values were adjusted using trophic enrichment factors (1.1‰ for δ13C and 2.8‰ for δ15N), shown alongside those of their potential food sources.
Fig 3.
Boxplots of stable isotope values (δ¹³C and δ¹⁵N) in whole blood samples of South Polar Skuas.
(a) δ13C of individuals (n = 39) at each breeding site. (b) δ15N of individuals (n = 39) at each site (CH: Cape Hallett; CW: Cape Washington; CM: Cape Möbius; and II: Inexpressible Island). Asterisks indicate significance levels from Tukey’s post-hoc pairwise comparisons between sites: ***p ≤ 0.001. **p ≤ 0.01.
Fig 4.
Isotopic niches (CI = 0.95) for South Polar Skuas (n = 39) from four breeding sites.
CH: Cape Hallett (n = 7); CW: Cape Washington (n = 12); CM: Cape Möbius (n = 14); and II: Inexpressible Island (n = 6).
Fig 5.
Estimated proportional contributions of potential food sources to the diet of South Polar Skuas at each breeding site.