Even in winter, some birds — including Black-capped Chickadees, House Finches, and American Robins — greet the sunrise with song. We normally hear the dawn chorus in springtime, when birds sing to define territory and attract mates. But birds don’t breed by warmth alone. Day length is a far more reliable spark than weather. We know that photo-receptors in birds’ brains sense the increasing light. It triggers the production of hormones, which helps bring on the breeding season. Our early birds aren’t breeding in February. But they’re warming up. Learn more at BirdNote.org.