4.3 Optimal foraging theory
Predatory animals may have a series of alternative foraging modes
(Kuwae, Miyoshi, Sassa, & Watabe, 2010). The optimal foraging theory
(Pyke, 1984) predicts that decisions on foraging strategy, including
what, where and how to hunt, are based on a maximization of currencies
(Bautista, Tinbergen, & Kacelnik, 2001). Therefore, in their natural
habitat, predators are expected to take different foraging strategies in
response to both prey abundance and vulnerability such that they attain
the highest energy intake rate.
As predicted by OPT, M. squamatus showed high behavioural
flexibility by adjusting its foraging methods and behavior profiles in
shallow and deep areas. In deep waters, where prey abundance and
vulnerability are lower, M. squamatus allocated most of the time
to repeated pursuit diving to minimize the foraging energy cost. This
strategy was awarded with bigger gains and resulting in comparable
energy gain as in shallow waters, where smaller preys are more abundant
and easier to catch. The wintering grounds of M. squamatus are
mainly mountainous streams (Zhao & Pao, 1998), which resources are
patchily distributed (Taylor & Warren Jr, 2001). The behavioural
flexibility is critical for predators foraging in heterogeneous
environment (Abrahms et al., 2020), where prey is patchily distributed
and may be unpredictable for diving birds (Tessier & Bost, 2020).