Table 5 Historical changes, based on recent and museum feather samples, in bulk stable isotope values, in trophic positions calculated from CSIA-AA and δ¹⁵N values of the trophic amino acid Glx (glutamic acid) and the source amino acid Phe (phenylanaline)

Rockhopper penguin

ns

t (5.6) = 5.3, P = 0.002

ns

t (5.9) = 5.3, P = 0.002

t (5.7) = 3.5, P = 0.014

Gentoo penguin

t (8.0) = − 3.6, P = 0.007

t (7.7) = 3.0, P = 0.018

t (6.6) = − 4.3, P = 0.002

ns

t (6.6) = 5.8, P < 0.001

Magellanic penguin

ns

ns

ns

ns

t (6.4) = 4.4, P = 0.004

Thin-billed prion

 Polar

t (8.0) = − 2.5, P = 0.035

t (4.4) = − 7.3, P = 0.001

t (6.9) = − 5.0, P < 0.001

t (5.4) = − 2.9, P = 0.032

ns

 Temperate

ns

ns

ns

ns

ns

Wilson’s storm-petrel

ns

ns

t (4.6) = 3.5, P = 0.007

ns

ns