Birds possess an extreme ability to regulate their own body temperature. On cold winter nights, they reduce their body temperature several degrees to save energy and increase their chances of survival. The disadvantage is that the birds become more lethargic, and there is a risk of becoming easier prey for predators.
Now, researchers have shown that supplemental winter feeding is good for great tits, at least for females. The females that had access to extra food in winter did not reduce their body temperature at night as much as females who received no supplemental food. Among males, no difference in their body temperature response was noted.
“We believe it is due to males being dominant, and they manage to secure sufficient food regardless of how much is available. Females, on the other hand, are subordinate and do not have priority access to food. If there is only a little food, males have priority and ensure that they eat enough to maintain a high body temperature”, says Johan Nilsson, biologist at Lund University.
The study was carried out in winter at Vombs Fure, a coniferous forest outside Lund. In one part of the forest, the researchers put out bird feeders. In another, the birds received no supplemental food. The researchers then measured and compared the birds’ body temperature at night.
Johan Nilsson points out that the study was carried out in a forest, and it is therefore uncertain whether bird feeding in cities is always good in general.
“What we can say, with certainty, is that females in nature benefit from being fed in winter”, he says.
Publication in Biology Letters: Predictability of food supply modulates nocturnal hypothermia in a small passerine
Johan Nilsson, researcher
Department of Biology, Lund University
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johan [dot] nilsson [at] biol [dot] lu [dot] se