This is Bird Note.

For small songbirds, surviving a cold winter night can be challenging.

Their bodies lose heat faster than those of larger birds,

so little birds have found resourceful ways to stay warm,

like huddling close together with others.

Some snuggle into old bird nests,

others shelter in a dense mass of leaves.

But the burden, a tiny bird of the southwest,

does something few other birds do to keep warm.

It builds special nests to roost in in the winter.

Desert nights are often cold, so warm roosts are crucial.

The birds build roosting nests all year long,

as well as breeding nests in the spring.

But the nests they build for the winter are smaller

and warmly lined with feathers and dry grass.

Birdons are prolific nest builders,

who have several nests at the ready.

This generous supply of snug bungalows can help other birds too.

In Arizona, one burden nest hosted 15 black-tailed net catchers,

all crammed in for five cold nights in a row.

For a burden, having net catchers crash in one of its nests

isn't a big problem.

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