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Hooded Merganser

Order: Anseriformes
Family: Anatidae
Genus/Species: Lophodytes cucullatus

Description

The Hooded Merganser is the smallest of the three species of mergansers, also known as saw-bills or fish-ducks, found in North America. All mergansers have slender elongated serrated bills tipped with a hooked nail. These bills are ideally suited for capturing and controlling the slippery fish that make up a large part of their diet. They are extremely agile swimmers and divers but awkward on land because their legs are set well back on their bodies.

Hooded Mergansers are highly sexually dimorphic. Both sexes have a bushy erectile crest of head feathers which forms the distinctive "hood". In breeding males this hood has a large central white patch boldly bordered in black. When the hood is down, the visible white is reduced to a narrow band trailing back from the bright yellow eye. Females and non-breeding males have brown hoods that match the rest of their plumage.

The breeding male has a black face, neck and back. The breast and underparts are bright white. Two bold black lines running down the side of the bird separate the white of the breast from the finely vermiculated rufous flanks. The upperparts of the wings are blackish with white striping on the flight feathers. The underparts of the wings are light grey to nearly white.

The plumage of the females and non-breeding males is dusky brown throughout, lighter on the underparts and a richer reddish-brown in the crest. They also have some white striping on the wings. Males have entirely black bills. Females and juveniles have some orange coloration at the base of the bill and on the lower mandible. Females have dark brown eyes.

Distribution and Habitat

The Hooded is the only merganser whose range is entirely restricted to North America. They can be divided into western and eastern populations. Western birds breed from Montana and Oregon north to southern Alaska. They winter along the Pacific coast from southern Alaska to California. The eastern population has a much larger range. They breed from the eastern half of southern Canada south through the United States from the Northern Great Plains and Mississippi Valley east to the Atlantic. The southern edge of their breeding range stops just short of the Gulf Coast. Breeding eastern Hooded Mergansers reach their highest concentration in the Great Lakes Region. Wintering birds concentrate in the coastal regions of south-eastern United States.

Breeding occurs in a wide variety of forested wetlands habitats including small lakes, beaver ponds, marshes, swamps, and river edges. Where man-made nest boxes are available they have been known to utilize treeless areas.

Diet

Hooded mergansers locate their prey visually, swimming with their faces submerged, surveying the water beneath them. Once prey is observed it is actively pursued underwater. Their diet includes fish, crayfish, frogs, mud crabs, clams, aquatic insects, and insect larvae. They have extremely muscular gizzards to help them grind down the exoskeletons of shellfish. Hooded Merganser ducklings are primarily insectivorous.

Reproduction

Male courtship behavior involves a number of elaborate displays featuring the erectile crest and distinctive vocalizations. One of the most common is the "Head-Throw". A male raises his crest and swims parallel to a female. He throws his head back sharply until it touches his back and then brings it forward slowly while emitting a rolling frog-like croak. Other ritual displays include wing flapping and stretching, shaking, or pumping the head. The female may bob or pump her head in response to the male's overtures. She solicits copulation by stretching her neck and head out just above the water and laying her tail flat on the water surface. Copulation occurs on the water and is preceded and followed by more highly choreographed displays by the male. Pair bonds dissolve once the female begins incubation.

Although woodpecker cavities in both live and dead trees in close proximity to water are their preferred nesting sites, active cavity nests have been found as far as 27 meters off the ground and 0.5 km from the nearest water. The female does not bring any additional nesting material to the cavity, but she will rearrange material already on site and complete the nest by plucking down from the brood patch on her belly. She lays 10-12 nearly spherical white eggs and incubates them alone for 29-33 days.

Within 24 hours of the last egg's hatching the mother surveys the surroundings for predators then calls her brood from the nest. They use sharp claws to clamber up the sides of the nest cavity to the entrance then make the long drop to the forest floor. The family must then make its way overland to the safety of water. Day old ducklings are very precocious, able to feed themselves and make short shallow dives. They respond to predators by diving or freezing in place in the cover of heavy vegetation. A female with a very young brood will perform a distraction display, feigning a broken wing as she attempts to lead the predator away from her ducklings. Mothers probably leave the young a month before they fledge at approximately 10 weeks of age.

Conservation

Habitat destruction and degradation has undoubtedly played a role in limiting the species. Forest management can be altered to preserve cavity trees and corridors of vital riparian habitat. Nesting cavities lost through logging practices can be partially replaced by programs providing artificial nest boxes. Water quality changes in many parts of the country due to increased sedimentation and water turbidity make it harder for mergansers to find food. Improving water quality and restoring natural hydrology in wetlands areas benefits the species.

Hooded Merganser numbers are difficult to assess due to their habit of dispersing widely in wooded habitat rather than gathering in large easily censused flocks. One researcher in the 1970s estimated that the total continental population was approximately 76,000 birds despite the fact that hunters were shooting that many birds every year according to U.S. Department of the Interior statistics. The true population is probably closer to 270,000-385,000 birds.


References

Del Hoyo, J., Elliot, A. and J. Sargatal. eds. 1992. Handbook of the Birds of the World. Vol. 1. Ostrich to Ducks. Lynx Edicions, Barcelona.

Dugger, B.D., Dugger, K.M. and L.H. Fredrickson. 1994. "Hooded Merganser (Lophodytes cucullatus)" In The Birds of North America. No. 98 (A. Poole and F. Gill, Eds.) Philadelphia, PA. The Academy of Natural Sciences; Washington, D.C.: The American Ornithologist's Union.

Madge, S. and H. Burn. 1988. Waterfowl. Houghton Mifflin Co., Boston.

Todd, F. S. 1996. Natural History of the Waterfowl. Ibis Publishing Co., San Diego, CA.