About Mergus serrator Linnaeus, 1758
The adult red-breasted merganser (Mergus serrator Linnaeus, 1758) measures 51–64 cm (20–25 in) in length, with a wingspan of 66–74 cm (26–29 in). Males are on average slightly larger than females: males weigh 950–1,350 g (34–48 oz), while females weigh 800–1,100 g (28–39 oz). This species has a spiky crest and a long, thin red bill with serrated edges. Breeding males have a dark head with a green sheen, a white neck, a rusty-colored breast, a black back, and white underparts. Adult females have a rusty head and a greyish-brown body. Juveniles resemble females, but have a shorter crest and slightly smaller white wing patches. The range of the red-breasted merganser overlaps broadly with that of the similar, closely related common merganser, so the two species can occur in the same location at the same time. Despite this overlap, the two species often favor different habitats: red-breasted mergansers prefer saltwater, while common mergansers prefer freshwater, though habitat overlap is still frequent. Breeding male plumages of the two species are fairly distinct, but females, immature birds, and non-breeding males of both species can be very hard to tell apart. Female common mergansers have more contrast between their darker head and lighter breast, plus a light chin patch that is not present on female red-breasted mergansers. Red-breasted mergansers dive and swim underwater to feed. They mainly eat small fish, but also eat aquatic insects, worms, crustaceans, and amphibians.
