Birds often seek protected places to roost or sleep at night, especially in the winter. Dense vegetation found in thickets or the interior branches of evergreens serve as a windbreak and conceal the birds from predators. A few species of songbirds – the ones that nest in tree cavities or bird houses – will also roost in cavities in the winter. Research has shown that these shelters, through reduction of wind speed, can increase the temperature by 40°F. Energy savings in one study ranged from 25% – 38% for birds roosting in cavities and resulted in an increased fasting endurance of six to seven hours in winter. Sometimes more than a dozen birds will pile into a single box or cavity to conserve heat. This may well have been the case in this pileated woodpecker cavity, given the amount of bird droppings found in it, or perhaps one lone chickadee took up residence night after night. (Judging from the droppings usually found in such cavities, mice use them for shelter even more than birds.)
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.