Oceanic thermal structure mediates dive sequences in a foraging seabird

1. Changes in marine ecosystems are easier to detect in upper-level predators, like seabirds, which integrate trophic interactions throughout the food web.

2. Here, we examined whether diving parameters and complexity in the temporal organisation of foraging sequences of little penguins (Eudyptula minor) are influenced by sea surface temperature (SST), water stratification and wind speed – three oceanographic features influencing prey abundance and distribution in the water column.

3. Using fractal time series analysis, we found that foraging complexity (i.e. temporal organisation of diving behaviour as expressed by long-range correlation or memory in the dive series) was associated with SST and water stratification throughout the breeding season, but not with wind speed. Little penguins foraging in warmer/more-stratified waters exhibited less stochastic foraging sequences likely as a response to prey aggregations nearby the thermocline. Ultimately, they showed higher foraging efficiency and numbers of dives, and lower mean dive depths than those foraging in colder/less-stratified waters.

4. Studied individuals devoted a greater proportion of their diving activity to exploration in colder/less-stratified waters, when environmental conditions are presumably more challenging and prey patches less predictable.

Methods
Methods are detailed in the associated manuscript.