A bird on the water might look like a duck and swim like a duck, but that doesn't mean it's a duck.

A handful of common water birds are often confused with ducks, but they actually belong to other groups of waterfowl. Here's a look at five such impostors.

Common loon (9 lb.) Largest of the duck-like waterfowl, it was introduced to nonbirders in the 1981 movie "On Golden Pond." Really too big to be confused with ducks, though it is a diver; black head and neck marked with an area of black and white stripes on the mid-neck; back resembles a black and white checkerboard; best known for its breeding season yodel. Look for loons during spring migration on large lakes and rivers.

Pied-billed grebe (1 lb.) A common breeder in wetlands and marshes; dark overall with a black ring around bill; bill is laterally compressed like a chicken bill; dives to feed on invertebrates, amphibians, and small fish.

Double-crested cormorant (3.7 lb.) An increasingly common sight at large lakes and rivers, often seen perched on emergent and shoreline dead trees. All black body, long bill with hook at tip, often described as a "big black duck with a long neck." Look for them up and down the three rivers and on Lake Erie.

American coot (1.1 lb.) The mascot of Cpl. Klinger's ("M• A• S• H") beloved Toldeo Mud Hens; all black body with white chicken-like bill; swims and dives like a duck; common in large wetlands and ponds and lakes with emergent vegetation; member of the rail family.

Common moorhen (11 oz.) Another rail fond of marshy habitat; less common than coots; dark charcoal gray body with yellow-tipped red bill; may be seen wading in shallow water or swimming in jerky fashion.

These are just a few of the duck-like waterfowl that can be encountered during spring migration in western Pennsylvania wetlands and along lake shores and rivers. Other imposters to watch for include red-throated loons (3.1 lb.), horned grebes (1 lb.) and ring-billed gulls (1.1 lb.). Armed with a good field guide and binoculars, even beginning birders should be able to identify most of these species.

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