In the U.S. we have three species of merganser, and the Hooded Merganser Lophodytes cucullatus is the smallest of the three. The male Hooded Merganser is also pretty spectacular, especially when it has its hood fully erect, as it often does at the time of year when pair bonds are being strengthened before the breeding season. I cam across this "Hoodie" as we call them in a flooded backwater while birding this morning. Hooded Mergansers are cavity nesting birds, building nests in hollow logs, old woodpecker cavities, or other natural cavities. They feed on a variety of water-related prey, and seem to especially favor crayfish, though small fish, insects, and crustaceans are also taken. Like other cavity nesting ducks like Wood Ducks they often lay their eggs in other ducks nests, both other Hooded Mergansers, and the nests of other cavity nesting species. Common Mergansers are the largest merganser species, and so Hooded Mergansers often lay their eggs in the nest of Common Mergansers, but because the much larger Common Mergansers often cannot fit into the nest cavity of the smaller Hooded Merganser the opposite is less common. Similar sized Wood Ducks and Common Goldeneye are other species where nest predation in either direction is considered common.
Here are some photos of the other commnon U.S. cavity nesting ducks along with this female Hooded Merganser:
Common Goldeneye Bucephala clangula
Common Merganser Mergus merganser (note that in Europe this species is called Goosander, and some experts feel that the two subspecies will be split to full species at some point)
Good birding.
