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.More info and transcript at BirdNote.org. Want more BirdNote? Subscribe to our weekly newsletter. Sign up for BirdNote+ to get ad-free listening and other perks. BirdNote is a nonprofit. Your tax-deductible gift makes these shows possible.