Friday, March 22, 2013

A Few Good Terns

This photo was taken on the causeway that runs downstream from the Oahe Dam near Pierre, South Dakota. This location, in my opinion, is one of the region’s premier birding spots. Interesting birds can be seen during any season. The huge Lake Oahe attracts vagrants like Long-tailed Ducks and jaegers and, as can be seen in this picture, a host of more common species. The Missouri River in South Dakota hosts both eastern and western North American birds.

Five species of gulls and terns loafed on the causeway. The gull in the foreground is a Ring-billed. The large bird behind the gull is a Caspian Tern. The black terns scattered throughout the background are Black Terns. Most of the gray and white terns in this photograph are Common Terns. The two terns with back sides to their heads and white crowns are non-breeding Forster’s Terns. A sixth species, a Least Tern, occurred nearby.

Although Forster’s Terns are more common than Common Terns in Minnesota, Common Terns are the most widespread North American tern. Note the Common Terns’ orange-red bills and grayish underparts. It is hard to see here, unlike in Forster’s Tern, the tails are usually shorter than the wingtips. All of these field marks can be subtile. I suspect the bird directly to the right and slightly behind the Caspian Tern is a breeding-plumaged Forster’s Tern. It is brighter white underneath and appears of have a more yellowish bill.

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