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