Abstract: Throughout evolutionary history, animals are finely
tuned to adjust their behaviors corresponding to environmental
variations. Behavioral flexibility represents an important component of
a species’ adaptive capacity in the face of rapid anthropogenetic
environmental change, and knowledge of animal behaviours is increasingly
recognized in conservation biology. In aquatic ecosystem, variation of
water depth is a key factor affecting the availability of food, thus the
foraging behaviours of many waterbirds, especially piscivores. In this
study, we compared the foraging behaviours of Scaly-sided Merganser
(Mergus squamatus ), an endangered migratory diving duck endemic
to east Asia, in habitats with different water depth
(Shallow water: 0-40cm; Deep
water: 40-300cm), using video camera records obtained from the known
wintering sites during three winters from 2018-2020. Further, the energy
expenditure of foraging behavior profile and energy intake based on fish
sizes were calculated to study the foraging energetics. In total, 200
effective video footages that contained 1,086 minutes with 17,995
behaviours and 163 events of catching fish were recorded. Results showed
that 1) time length for fishing (including eye-submerging, head-dipping,
diving and food handling) of Mergus squamatus in shallow waters
was significantly more than in deep waters; 2) Mergus squamatusspent significantly more time for preparing (including vigilance,
preening and swimming) in deep waters than in shallow waters; 3) the
mean catch rate was 0.28 fish/minute in shallow waters, which is
significantly higher than the value of 0.13 fish/minute in deep waters;
4) despite the distinct foraging behaviour profiles and energy intakes,Mergus squamatus showed similar energetics in shallow and deep
waters. We concluded that Mergus squamatus is a good example of
behavioural flexibility that aligns with expectations of optimum
foraging theory, in that it behaves in accordance to resource
availability in different environments, resulting in high foraging
efficiency. The behavioural flexibility can be related to its evolution
history.
Keywords : Foraging behaviours adaption; Foraging energetics;
In-stream habitats; Morphological specialization.