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Posted by Ken Schneider on 13:59:33 03/29/08
The Red-breasted Mergansers are still on our lake, and still cruising endlessly around the perimeter of our lake. Watching them closely led me to form a hypothesis about their fishing technique. Is it possible that they are actually engaged in cooperative feeding? Almost always, one or two would lead the group, and the rest tailed off a little ways behind. The group will course along quite rapidly, with heads or even half their bodies underwater. Suddenly, they would stop, and they would converge on a school of fish. The leading birds, which appeared to overshoot the school, would then retreat back in to join the others at the shoreline. Could they have been "herding" the fish?
I asked Google about it, and to my great surprise, one of the first hits was "Cooperative feeding behavior in Red-breasted Mergansers," a 1965 article in The Auk, in which Bayard H. Brattstrom of California State College at Fullerton makes this same observation. He states that this behavior, while reported previously in cormorants, had never been described in mergansers. I was only 45 years late!
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