This is bird note.

When the bitter cold of winter arrives, songbirds face an emergency.

How to keep warm through the night.

On normal nights, many prefer sleeping solo in a sheltered

spot but in severe cold some kinds of birds may have a greater prospect of

survival by roosting with others.

The tiny Eurasian wren is a common garden bird in England,

quite similar to the winter wren of the US.

And both are expert snugglers.

In England, nine Eurasian wrens hunkered together in an old song thrush nest

and an astonishing 46 packed into a vacant nest box.

Some of the wrens came from a mile away to seek the warm company of their peers.

In the US 31 winter winter ends were found squeezed together in a nest box. Bluebirds and nut hatches will also cluster in nest boxes or tree hollows during extreme weather.

When masked together like this, birds may crouch in layers on each other's backs.

Some of these species also nest in cavities during the warmer months.

Perhaps because of this, they may be more inclined to tuck up together in a warm enclosure

on those bitter nights.

For Bird Note, I'm Michael Stein.