Cephalopods in the diet of nonbreeding black-browed and grey-headed albatrosses from South Georgia
Résumé
The food and feeding ecology of albatrosses
during the nonbreeding season is still poorly known, particularly
with regard to the cephalopod component. This
was studied in black-browed Thalassarche melanophris
and grey-headed T. chrysostoma albatrosses by analysing
boluses collected shortly after adults returned to colonies at
Bird Island, South Georgia (54S, 38W), in 2009. Based
on stable isotopic analyses of the lower beaks, we determined
the habitat and trophic level (from d13C and d15N,
respectively) of the most important cephalopods and
assessed the relative importance of scavenging in terms of
the albatrosses’ feeding regimes. Based on lower rostral
lengths (LRLs), the main cephalopod species in the diets of
both albatrosses was Kondakovia longimana, by frequency
of occurrence (F[90 %), number (N[40 %) and mass
(M[80 %). The large estimated mass of many squid,
including K. longimana, suggests that a high proportion
([80 % by mass) was scavenged, and that scavenging is
much more important during the nonbreeding season than
would be expected from breeding-season diets. The
diversity of cephalopods consumed by nonbreeding birds in
our study was similar to that recorded during previous
breeding seasons, but included two new species [Moroteuthis
sp. B (Imber) and ?Mastigoteuthis A (Clarke)].
Based on similarities in LRL, d13C and d15N, the squid
consumed may have been from the same oceanic populations
or region, with the exception of Taonius sp. B (Voss)
and K. longimana, which, based on significant differences
in d15N values, suggest that they may have originated from
different stocks, indicating differences in the albatrosses’
feeding regimes.