Chilly weather poses its own challenges for birds. if you spend your life beating gravity you need to be light, so birds can't afford to put on a little timber around the middle. here are some tricks they've evolved to survive the season's cold, wet and wind.
Survival by degrees
Like us and other mammals birds are endothermic, meaning they produce heat from within their bodies. Unlike us, they can also alter their temperature quite a bit depending on their needs. A small bird like a blue tit can save a third of its night-time energy budget by dropping its body temperature by around 8°C, a trick called nocturnal facultative hypothermia. The downside of this strategy is that they’re more vulnerable to predation.
Big yourself up
Many birds appear to swell in size on particularly cold or windy days. They’re ﬂufﬁng up their feathers, with muscles at the base of each shaft causing them to stand more upright and trapping more air. If they’re still feeling the chill, birds can shiver just like us to create extra metabolic heat. It’s a last-ditch strategy, though, as it uses up precious fat reserves.
Sun bathing isn’t a pastime you’d associate with winter. However any of the sun’s energy – even if it’s weak and wintry – can give birds a degree or two of free heat; even a degree up the scale is one degree a small bird doesn’t have to ﬁnd from its own heat budget. So look out for birds huddled in those sheltered sun traps. Out in the wild, anywhere that gets ﬁrst sunlight is a good place to concentrate your bird watching efforts.
Birds of a feather
A thrush has around 2,500 feathers, all playing a big role in winter survival. Different layers do jobs analogous to our own clothes. The down works like your thermal underwear, trapping heat radiated by the body in pockets against the skin. Like the shell layer of a waterproof jacket, the outer feathers are coated with oils from the preen gland to keep rain out. The contour feathers’ tightly interlocking barbs and barbules keep the wind off, reducing the chill factor and exposure risk.