Southern Giant Petrel counts and Magellanic Penguin fledging weights

Southern Giant Petrels (Macronectes giganteus) are important consumers
that range across the oceans throughout the southern hemisphere. In
Argentina, previous studies have shown they eat primarily pinnipeds and
penguins, which they are assumed to scavenge, although there are
occasional anecdotes of them attacking living penguins. Here we describe a
predation attempt by a trio of Southern Giant Petrels on a molting adult
Magellanic Penguin (Spheniscus magellanicus) at the large colony at Punta
Tombo, Argentina. We relate giant petrel attendance patterns at the colony
to the penguins’ phenology, showing how giant petrel numbers rise with the
increasing prevalence of vulnerable penguins. We suggest that living
penguins—both fledglings and adults—may constitute a more seasonally
significant proportion of the giant petrel diet than previously assumed,
and their capture may represent a specialized predation technique.