How do birds find their prey when hunting in muddy water?

This week's question comes from Craig Smith in Saanich, British Columbia. He asks: 

As I squat at the bank of the Fraser River, I see cormorants, grebes and mergansers catching small fish. When I poke my finger in the water, it is so muddy and opaque that I cannot even see my fingernail. So the question is, how do birds catch their dinner if they cannot see their prey?

Scott Reid, an associate professor of biology at the University of British Columbia suggests that birds usually rely on vision to hunt in water, provided that it is clear. But when a river, for example, becomes cloudy or muddy, their sensory abilities are much more limited.

For the local birds along the Fraser River there is some evidence that suggests they use their beaks to feel for fish when the water is not clear. They may move their beaks from side to side in the hopes of randomly locating a fish, or poke into crevices where the prey may be hiding.