Monday, April 29, 2013

Diving Horned Grebe

Horned Grebes usually feed in water six meters or less in depth (Stedman 2000). Last week I photographed this grebe in Goodhue County, Minnesota, along Lake Byllesby. I believe the water under this bird is about a meter deep. These grebes swallow small prey under water, but disable larger prey with their bills on the surface. They will also occasionally take flying insects from the air or glean other arthropods from the water surface. About 35% of their diet is fish, while 46% is insects—the rest is composed of crustaceans, small frogs, salamanders, leeches and tadpoles (Stedman 2000). Dives last for up to a minute.
As you can see in the final series of photographs, Horned Grebes are foot-propelled divers. First the grebes flatten their plumage to expel air from between the feathers and their bodies. As they begin their dives, Horned Grebes can spread their feet and legs out to the left and right—this allows them to leap almost straight up and then arch down into the water. When diving, they do not use their wings, which are only used underwater to make sharp turns or avoid danger. In the final photo, only a small splash of water remains—a splash that would please an Olympic diver. A close examination of these photos also reveals that drops of water remain on the grebe’s back throughout the dive!

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