How birds maintain their body temperature - Story and photographs by Don Cowie
Common sense tells us that when we are cold seek out the sun and when we are hot, look for some shade. However, we also know that it is not quite as simple as that in practise and birds employ many strategies to keep their body heat between the core 40-42 degree band that maintains life.
Many bird species adopt the simple process of sunning themselves, particularly in the early mornings when their body temperatures are at a low due to cold night time temperatures.
Doves are commonly seen ‘sunning’ themselves, lying on the ground their wings spread out to expose as much of their body surface to the rays of the sun as possible. They will also raise their wings alternately in an upright position while lying on their sides to warm the undersides. Birds such as herons and egrets can be seen perched on the tops of trees taking advantage of the early morning sun. Cattle Egrets fly off from their night time roosts in large numbers to their feeding grounds as soon as their body temperatures are sufficiently raised. Birds that spend a great deal of time in water such as cormorants and darters can regularly be seen with their backs to the sun wings outstretched their black feathers acting like solar panels soaking up the warmth from the sun. Black Crakes clamber up fallen rushes and sun themselves their wings drooping down to expose as much surface area to the sun as possible.
Many smaller birds such as manikins, finches sociable weavers and waxbills will seek shelter at night in their own nests or those of other species. Bronze mannikins will roost in their old breeding nests often re-lined with plant material for the cold months or will construct elongated tunnel shaped nests especially for roosting purposes, and many birds will cram into them at night huddling together to benefit from shared body heat. Numbers of black-cheeked waxbills will utilise the old nests of white-browed sparrow weavers or Buffalo Weavers communally at night for the same purpose. Species that utilise nests for shelter can benefit by 5-10 deg C above the external ambient temperature.