Shallow divers, deep waters, and the rise of behavioural stochasticity

Little penguins (Eudyptula minor) have one of the widest geographic distributions among penguins, exposing them to variable ecological constraints across their range, which in turn can affect their foraging behaviour. Presumably, behavioural flexibility exists to allow animals to adapt to prevailing environmental conditions throughout their foraging range. This study examined whether complexity in the temporal organization of foraging sequences corresponds to characteristics of the foraging area across four colonies geographically distributed along the entire species’ range. Complexity and fractal scaling in spatiotemporal patterns of foraging behaviour have been theoretically linked to foraging efficiency in heterogeneous environments. Using fractal time series methods (detrended fluctuation analysis), we found that foraging complexity along a stochastic–deterministic gradient was associated with bathymetry in local foraging areas; little penguins foraging in deeper waters produced more stochastic/less deterministic foraging sequences than those foraging in shallower waters. Corresponding data on fledging success suggest that little penguins foraging in deeper waters also experienced reduced reproductive success. A principal component analysis further showed that our fractal scaling index, which specifically measured the degree to which sequences are long-range dependent (a deterministic phenomenon), correlated positively with foraging efficiency (prey encounter per unit time) and negatively with foraging effort (total time underwater). Our statistical models showed that production of complex foraging sequences with high degrees of stochasticity appears to be energy intensive. However, we could not determine which strategy would have maximized foraging success, a variable we could not measure, under the conditions observed. We propose that increasing stochastic elements in foraging behaviour may be necessary under challenging environmental conditions, but it may not be sufficient to match fitness gains attained under more favourable conditions.