Foraging dynamics of little penguins in a hotspot of ocean warming
thesisposted on 2022-03-28, 10:14 authored by Gemma Carroll
In an era of rapid environmental change, predators can act as sentinels of shifts in ecosystem structure. By studying when, where and how much prey predators find under different foraging conditions, we can gain insight into how environmental changes affect food webs. Advances in bio-logging technology have opened a window into animal lives, and it is increasingly possible to identify feeding behaviour by cryptic predators under natural conditions. By linking feeding events to key physical and biological parameters, we can improve our understanding of the factors underpinning prey availability and predator ecology in complex and changing systems. In this thesis, I explored factors that influence prey capture by little penguins (Eudyptula minor) off the southern east coast of Australia. This region is a hotspot of global ocean warming, owing to the intensification of the warm, nutrient-poor East Australian Current. The pelagic food web in this area remains poorly characterised, and it is unknown how the system will respond to increasing oceanographic change. Understanding interactions among predators, prey availability and the physical environment can therefore provide a lens through which to explore changes in the East Australian Current ecosystem. I developed a prey capture signature from accelerometry to identify feeding events by wild penguins. Using this index, I showed that prey capture was related to sea surface temperature at multiple spatial and temporal scales. Penguins usually caught prey in foraging habitat associated with the coolest available temperatures, and high offshore temperatures (> 21oC) were related to low prey capture rates. I showed that patterns of prey capture by penguins matched independent estimates of the distribution of prey at nested spatial scales. I also found that penguins exhibited a flexible foraging strategy in this dynamic environment, incorporating information on prior foraging success and in situ conditions. These findings present new perspectives on predator prey interactions and resource availability in the pelagic ecosystem off eastern Australia, providing a foundation for future examination of this food web as the East Australian Current intensifies.