The sea is the limit: Foraging ecology of breeding Antarctic Procellariiformes

In the dynamic marine environment, highly mobile predators are expected to select profitable foraging areas, especially when provisioning young in addition to meeting their own energy needs. Knowing how and where animals choose to forage is not only important to advance ecological theory, but also to assess and mitigate the impact of anthropogenic threats. In this thesis I examine the breeding-season foraging behaviour of several of the Procellariiformes, a wide-ranging, long-lived group of seabirds, many of which have experienced steep population declines since the mid-20th century. Advances in biologging technologies over the last four decades have made it possible not only to accurately track individual movements, but also to identify important behaviours at sea. In my first data chapter (Chapter 2), I combine data from multiple tag types to describe diving behaviour in three albatross species, and discuss the implications for both foraging ecology and bycatch susceptibility. Moving from foraging capability of the individual to foraging preferences at the level of genus, in Chapter 3 I analyse the divergent niches of a summer- and a winter- breeding species of Procellaria petrel. Here I compare the habitat preferences of Grey Petrels and White-chinned Petrels breeding at Gough Island and South Georgia, respectively. Using high-resolution remote sensing environmental data, I identify divergent foraging preferences in dynamic habitats. Finally, in Chapter 4, I compare habitat preferences and accessibility between the two species of Phoebetria albatrosses across six colonies. While most studies of habitat preference consider only a single species or site, here I investigate whether closely-related species inhabit the same ecological niche at sympatric and allopatric colonies throughout their range. I show that Light-mantled Albatrosses have a consistent foraging niche, whereas Sooty Albatrosses select different habitats in sympatry and allopatry. I then discuss the impact of interspecific competition on plasticity in habitat preferences in general. Overall, my thesis examines diverse aspects of seabird foraging ecology from the individual to community level, discusses habitat preferences (and their potential flexibility) in relation to species' evolutionary history and as drivers of community structure, and considers the implications for conservation planning.

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