First-winter birds differ from adult females in appearance in that they have a grey-brown neck and upper parts; the upper parts of adult females are much darker — nearly black. Furthermore, the young birds have narrower white edges to their tertial feathers than adults do. Females of all ages are dark-eyed, whereas in males the eyes become pale during their first winter. Hooded mergansers are short-distance migrants, and they winter in the United States in regions where winter temperatures allow for ice-free conditions on ponds, lakes and rivers. They have two major year-round ranges. One is in the Eastern United States from the southern Canada–US border along the Atlantic Coast to the Gulf Coast in the region of the Mississippi delta. A smaller year-round range extends from Washington state and southern British Columbia to northern Idaho. They also breed to some extent in regions from Missouri to southern Canada and from Nova Scotia to eastern North Dakota and Saskatchewan, migrating when necessary to avoid winter conditions. For preference the hooded merganser lives on small bodies of water such as ponds and small estuaries where there is ample emergent aquatic vegetation, but it also inhabits larger wetlands, impoundments, flooded timber, and rivers. They prefer fresh water but do occur on brackish water bodies as well. Although the hooded merganser is a common species in captivity in Europe and most specimens recorded in the wild are regarded as escapes, a small number of birds have been regarded as genuinely wild vagrants. Britain's current first accepted record is a bird which was seen on North Uist in October 2000. Small numbers are seen regularly in Dublin, but these are presumed to be escapes. The hooded merganser is a diving predator that largely hunts by sight while under water. Most studies report that its diet varies according to circumstances, usually being dominated by fishes (44-81%). In addition it feeds on aquatic insects (13-20% of its diet) and other aquatic invertebrates such as crabs and crayfish (22-50%). Males and females of the hooded merganser form monogamous pairs and they remain together until the female has selected a nesting cavity and completed laying her clutch. After that, the male leaves the female to incubate and care for the brood. Females will actively seek out cavities in dead trees or artificial nest boxes such as those provided for nesting wood ducks. They prefer cavities 4–15 feet off the ground. Breeding occurs anytime between the end of February and the end of June, depending on the region.