Ravens feed on dead carcasses in winter. Carcasses are hard to find, hard to break into because the surface can freeze. Ravens aren t common either. Heinrich saw 15 ravens eating a dead moose. Thought that ravens had yelled to attract other ravens.
Birds are one big family.
Birds should be related. Hauled out dead cow carcasses to see if first ravens would yell. Froze butt off. First ravens didn t yell or sometimes yelled when carcass was already opened. Birds should stop yelling once there are lots around.