4.3 | The effect of capture event on fat score change
in winter
Interestingly, we found that robins that had previously been captured
tended to have more fat reserve in all three models. Two possible
hypotheses were constructed from this result: (1) birds perceive capture
as a heightened predation risk and respond by reducing body mass or (2)
birds perceive capture as an interruption to foraging and respond by
increasing body mass. Our results supported the second hypothesis and
were consistent with a previous study on great tit (Parus major ),
in which the body size of the bird showed a significant increase on the
day after capture and persisted for one week (Duarte, 2013; Macleod and
Gosler, 2006). Meanwhile, from a physiological perspective, a capture
event could cause acute stress and additional status change. During an
acute stress response, the adrenal gland of the bird secretes
corticosterone via the hypothalamic–pituitary–adrenal axis (HPA). The
initiation of HPA would then result in increased synthesis of
glucocorticosteroids that mediate behavioral and physiological changes
(such as an increase in body mass) to help the organism cope with the
stressor (Dickens et al., 2009). This outcome can be a reference case
for further study using classical ornithological field study methods,
helping to analyze disturbance caused by human capture.