Overview
Common Mergansers are the largest of the three merganser species, and among the largest ducks in North America, with a circumpolar distribution. Their breeding range in North America is in boreal forest rivers and lakes from Alaska across Canada to Newfoundland and Labrador, south to include western mountain range lakes and rivers to about Colorado, and in the northeast south to about Pennsylvania. Males have an iridescent dark green head with a narrow scarlet-orange bill, a bright white neck, breast, and sides, while the back and tail are gray. Females have a rusty brown head with a scarlet-orange bill, a very distinct white chin patch, and a gray breast, back and wings. In flight, they appear slender with a pointed profile, and the wings show substantial white on the secondary feathers. Common Mergansers are cavity nesters and readily use appropriately sized nest boxes. They winter near the ice line and are usually found in freshwater.
Description
Key Identification Features
- Males have an iridescent dark green head with a narrow scarlet-orange bill, a bright white neck, breast, and sides, and the back and tail are gray.
- Females have a rusty brown head with scarlet-orange bill, a very distinct white chin patch, and a gray breast, back and wings.
- In flight, they appear slender with a pointed profile, and the wings show substantial white on the secondary feathers.
Male/Female Average Length and Weight
- Mass: Males 2.6–4.8 lbs.; Females 1.9–3.9 lbs.
- Wing Length: Males 9.4–11.1 in.; Females 9.1–10.2 in.
Male Identification
- Alternate (Breeding) Plumage: The head and upper neck are iridescent deep green, which may appear black, and the rear of the crown may appear elongated but lacks an obvious crest. The lower neck, breast, sides, and belly are creamy white. The back and tail appear gray to black. The bill is narrow, long, and scarlet orange with a notable nail. The wings are dark gray, and in flight show an extensive white patch on the greater and secondary coverts and secondary feathers.
- Basic Plumage: Plumages are similar between the sexes, overall brownish-gray, with a white belly.
Female Identification
- Alternate (Breeding) Plumage: The head is rusty or reddish brown, has a long, narrow scarlet-orange bill, and has a shaggy crest. There is a sharply defined white patch on the lower chin, just behind the lower mandible. The lower neck, breast and flanks appear gray, and the flanks may have a mottled gray appearance. The back appears bluish gray.
- Basic Plumage: Overall brownish-gray with a white belly.
In-flight Identification
- In flight, they appear slender with a pointed profile with dark gray wings with a notable white patch on the inner six secondary feathers. The belly is creamy white.
Vocalizations
- Typically, silent. Males in courtship may emit a “kragagagagaga” during courtship flights. Females give harsh “karr” or “grock-gruk-gruk” when alarmed.
Similar Species
- Red-breasted Mergansers: May be confused with Red-breasted Mergansers, but male Common Mergansers have no crest on the head, a white breast and sides, and a brown iris, whereas male Red-breasted Mergansers have a notable crest, reddish brown breast and sides, and a red iris. Female Common Mergansers have a very notable, clean white patch on the chin behind the lower mandible. Red-breasted Mergansers have a slightly upward curved bill, whereas Common Merganser bills are straighter, and have a heavier appearance. While not completely dependable, in winter and migration Common Mergansers are far more frequently associated with freshwater near the ice line, while Red-breasted Mergansers are more frequently associated with brackish and saltwater habitats.
Habitat Preferences
- Breeding: Common Mergansers are typically found in boreal freshwater lakes and rivers.
- Migration and Winter: They are most frequently found on larger freshwater lakes, and rivers usually in small flocks in the winter.
Foraging Habits and Diet
- Common Mergansers feed heavily on a variety of species of fish in North America. They are visual predators and forage extensively on fish but may eat aquatic insects during the breeding season.
Breeding Habits
- Monogamy: Common Mergansers are seasonally monogamous, with pair formation during late winter and early spring. Males leave with onset of incubation.
- Nest Location: Usually a cavity nester occupying tree hollows and will readily use nest boxes, occasionally will nest on the ground in spaces among tree roots or holes in banks along rivers. Females may add down or small amounts of grass to cavity nests.
- Clutch Size: 8 to 12 eggs. Female may also lay in nests of other females, resulting in abnormally larger clutch sizes up to 17 eggs. The eggs are sub-elliptical, white to creamy white, and are 2.6 by 1.8 in. The incubation period is approximately 28 to 35 days.
Migration & Distribution
- Fall Migration: A late fall migrant, they likely depart lakes and rivers with the onset of freeze-up in late October or November. Often winter near the ice line.
- Spring Migration: Spring migration occurs in February–April with arrival on breeding areas often timed with ice-out, in March to May depending on latitude.
Conservation Status
- IUCN Status: Least Concern
- Population Status: The North American population estimate is roughly estimated at 600,000–1,000,000 birds. Limited data suggests that the population is stable.
- Conservation Concerns: Habitat degradation including a lack of suitable nesting cavities presents a challenge to their populations as does river channelization and increased sedimentation. Pollutant exposure is also a concern, including acid rain which impacts their supply of fish prey.
- Conservation Focus: Improving water quality, protecting freshwater wetlands in their breeding and wintering habitats, and providing supplemental nesting opportunities through nest boxes can help to support the species.
Harvest Information
Please note that harvest information for Common Mergansers and Red-breasted Mergansers has been combined in the following data.
- An average of 27,648 Common/Red-breasted Mergansers were harvested annually across the US from 2019 to 2022.
- Common/Red-breasted Merganser harvest is typically highest in the Atlantic Flyway, accounting for 50 to 60 percent of the total US harvest.
- The top three states for Common/Red-breasted Merganser harvest, based on annual averages across the 2019–2022 hunting seasons, were New York (6,165), Wisconsin (1,808), and Pennsylvania (1,707).
