What are crows saying when their loud cawing fills a dark winter’s evening? Despite the inescapable ruckus, nobody knows for sure. Birds congregate daily before and after sleep, and they make some noise, but what might be happening in those brains is a mystery.Curious about these raucous exchanges, researchers at the University of Washington Bothell are listening in. They are placing equipment on the roof of their building — a meeting place for some of the thousands of crows that sleep in nearby campus trees — and using a sort of computerized eavesdropping to study the relationship between calls and the birds’ behavior.