How Do Birds Stay Warm?

The temperatures in the Colvin Run Habitat have been brutally cold (for the US mid-Atlantic region), ranging from near zero to a few degrees above freezing with nighttime and early winds of ten to twenty knots. So how do the small birds that are wintering in the Habitat stay warm?

>They fluff their feathers, which traps air between their feathers and bodies. The result is a natural layer of insulation. In a related manner, when they sleep the birds tuck their bills under their wing feathers so as to breath in this warmer air.
>They eat which gives them the energy to shiver. As in humans, the shivering generates warmth. In the last week, the birds are consuming seed and suet at nearly three times the normal year round rate.
>They seek shelter out of the wind and cold. Some, such as the titmice, huddle together in natural shelters.
In the Habitat are three Hellera Holly bushes that the birds, as well as the squirrels and some times the fox, use for shelter. In the first photo (click on the photo to get an enlarged photo), you can see that this is really a very overgrown holly shrub that measures about ten feet square. The inside is a dense tangle of branches covered by small holly leaves that does not allow rain or snow to pass. Notice in the first photo, arrows shows two starlings and a white-throated sparrow on the outside covering of one of these holly bushes.
In second photo, a white-throated sparrow has just come from roosting inside. In the third photo, the white-throated sparrow is flying out, while a starling is flying into the bush. In the fourth photo, a bird is entering the bush in a well-worn opening created by the squirrels and the fox. With the exception of the woodpeckers, nearly all of the small songbirds in the Habitat are seen on, in, and through these holly bushes.
With the snow and sleet predicted this coming week, these holly bushes will provide a haven for the birds.