The red-breasted merganser (Mergus serrator) is a waterfowl species with clearly expressed sexual dimorphism – the female and male are very differently colored. When stretched, it measures between 51 and 62 cm, and the wingspan ranges from 70 to 86 cm.
The female is unobtrusively camouflaged. It wears fairly uniform gray- and brown-colored plumage. It is characteristic for her that the brown color of the head and cheek on the neck smoothly transitions into the gray body. Her belly and chest are light gray, the flanks, back and wings are dark gray. Toward the end of the wings she has a snow-white stripe. Her bill is long and fairly evenly slender at the base. The bill is red on the underside and black on the upper side.
The male, with its contrasting iridescent plumage, is the exact opposite of the female. Similar to the female, the male also has tufted plumage at the back of the head, but his head and cheeks in nuptial plumage are metallic, iridescent dark green. A notable ornament of his green head is the blood-red eye, and the red lower mandible and the black upper mandible provide a beautiful color feature. On the neck the male has a white collar, and almost all of his wings are white. The back is black, the flanks gray, and the belly dirty white. Also characteristic for him are reddish-brown breasts with a pattern of black spots.
The red-breasted merganser is a migratory bird that prefers to overwinter along coastal shores. It returns to breeding areas in Scandinavia and the northern parts of Great Britain, North America, Russia and Asia, and to the southern part of Greenland, in spring. It most often nests on deep lakes or moderately fast-flowing rivers, whose banks are wooded; as well as in calm sea bays. In April and May groups of males with wedding displays compete for the females. When a pair is formed, the female searches for a suitable nesting site. The nest is well hidden among the roots of shore-side shrubs or trees, in a hollow in the ground, under a large rock or in a burrow dug by some other animal. The nest, which is usually hidden only a few tens of meters from the water, is lined with feathers and vegetation for greater comfort.
This is a diurnal bird that feeds mainly on smaller fish, so we can observe it only in places where nature is sufficiently preserved to sustain sufficiently large fish populations. Its diet is supplemented with aquatic invertebrates, especially insects and crayfish, and with aquatic vegetation. In our country the red-breasted merganser does not nest, but on the coastal area and nearby it winters regularly. It can also be observed during migration, when it stops at a lake or river in our region to regain energy for the journey ahead.
