Following in the footsteps of John Warham: quantifying the ecological factors that underpin the post-moult nonbreeding foraging of Eudyptes penguins

Knowing how marine predators utilise the high seas against a changing marine environment is crucial for informing management and conservation. Eudyptes penguins are the most diverse and abundant penguin genus in the world and range from the subtropics to maritime Antarctica. The genus includes eight extant taxa (seven IUCN recognised taxa) which include the southern rockhopper penguin (Eudyptes chrysocome), eastern rockhopper penguin (Eudyptes chrysocome filholi), northern rockhopper penguin (Eudyptes moseleyi), Snares penguin (Eudyptes robustus), Fiordland penguin/tawaki (Eudyptes pachyrhynchus), macaroni penguin (Eudyptes chrysolophus), erect-crested penguin (Eudyptes sclateri) and royal penguin (Eudyptes schlegeli). While these penguins are a conspicuous and charismatic component of island ecosystems throughout the Southern Ocean, there remains a large gap in our knowledge on several aspects of the ecology of Eudyptes penguins including how these penguins utilise their marine environment.
Despite their abundance, several of these taxa have undergone population declines over the past century. Of the seven listed Eudyptes taxa, four are listed as Vulnerable and three are listed as Endangered, however they are among the least researched group of penguins in the world. Australasian Subantarctic islands hold the largest diversity of these penguins, with Snares, royal, Fiordland/tawaki and erect-crested penguins being confined to the area. Two different taxa can typically breed in sympathy, and the five taxa on the Australasian Subantarctic Islands breed in close proximity. These penguins perform a post-moult nonbreeding migration when they leave their colonies and disperse into the Southern Ocean, without returning ashore, for up to 6 months. Each year during this nonbreeding season millions of individuals of Eudyptes penguins disperse into the Southern Ocean, which generates questions regarding niche partitioning between closely related and/or sympatric populations, the roles energetics and oceanic currents play in influencing migration routes and how climate change may affect these populations in a rapidly changing marine environment.
Chapter 1 provides the context for the work presented in this thesis. Chapter 2 is a synthesis of the post-moult nonbreeding tracking data available for seven taxa of Eudyptes taxa across the Southern Ocean, representing 585 individual birds across 28 colonies from 13 island groups, all processed, published and/or archived during this project. Chapter 3 explores niche partitioning between two closely related and recently diverged lineages of Eudyptes penguins, Fiordland penguins/tawaki and Snares penguins, with an annual cycle offset by 8 weeks (referred to as allochrony) by comparing utilisation overlap indices of the observed migrations and a hypothetical scenario where both taxa commenced migration simultaneously. The results suggest that allochrony did not arise to reduce interspecific competition during the post-moult nonbreeding season. Rather, allochrony is likely to be at the root of segregation because the relative profitability of the different water masses that the penguins forage in changes seasonally which results in the two taxa utilising different areas over their core nonbreeding periods.
Chapter 4 examines the post-moult nonbreeding distributions of eight populations (from four taxa) of Eudyptes penguins from the Australian Subantarctic region to explore how spatiotemporal partitioning may influence the distributions of migrations and their associated cost of transport and prey availability. The migration routes allow niche partitioning but require trade-offs between energy needed to perform the migrations and potential energy gained in terms of prey availability. Chapter 5 collates the largest Southern Ocean wide tracking dataset for southern rockhopper, eastern rockhopper, northern rockhopper and macaroni penguin, the four most abundant and widely distributed taxa of the Eudyptes genus, to investigate habitat selection and the potential for