Abstract
Winter, the most challenging season for animals, is usually accompanied
by extremely cold temperatures and limited food resources. Harsh winter
conditions force birds to develop behavioral and physiological
adaptations to reduce mortality. Birds might select for sexual
segregation to reduce conflict between different social hierarchies at
the population level. They can also adjust their body conditioning via
fat reserve to balance the trade-off between starvation and predation at
the individual level. Using mist-netting surveys and bird banding, we
traced 61 orange-flanked bush-robin (Tarsiger cyanurus ), an
abundant and easily-observed long-distance migratory bird exhibiting
delayed plumage maturation, to better understand the winter adaptation
of these songbirds. We found that the number of 2yr+ adult males with
bright-blue plumage was significantly lower than the number of males
with olive-brown plumage. However, the sex-ratio was only slightly
skewed to males with olive-brown plumage, suggesting that habitat-type
influences sexual segregation. This robin tends to become heavier and
store more fat over the course of winter, as they can fine-tune their
fat reserve in response to changes in weather (including temperature,
humidity, and snowfall) and food abundance. Interestingly, capturing the
birds may also have a significant positive effect on their fat reserve.
Overall, these results improved our understanding of the flexibility in
adaptation of small passerine birds wintering in a subtropical forest
and provided vision for considering the inevitable influence by
ornithology field methods.
Keywords: Tarsiger cyanurus ; winter; fattening strategy;
sex ratio; sexual segregation; adaptation