The red-breasted merganser and common merganser are two closely related species of diving ducks found throughout North America. Both belong to the genus Mergus and are medium-sized, long-bodied ducks with thin, serrated bills used for catching fish. While the two merganser species have similar appearances and behaviors, there are some key physical and ecological differences between them.
Quick Facts
Red-breasted Merganser
- Species: Mergus serrator
- Other Names: American merganser, sawbill
- Length: 22-25 inches
- Wingspan: 30-36 inches
- Weight: 1.5-2.4 pounds
- Coloring: Male has green head, white neck collar, rusty red breast. Female has gray-brown head and body.
- Diet: Fish, aquatic insects, crustaceans
- Habitat: Lakes, rivers, coastal areas
- Range: Breeds in Alaska and Canada, winters along Pacific, Atlantic and Gulf coasts of U.S. and Mexico
Common Merganser
- Species: Mergus merganser
- Other Names: Goosander
- Length: 23-28 inches
- Wingspan: 30-35 inches
- Weight: 2.1-3.6 pounds
- Coloring: Male has green head, white body and neck. Female has gray-brown head and body.
- Diet: Fish, aquatic insects, crustaceans
- Habitat: Lakes, rivers, estuaries
- Range: Breeds across Canada and Alaska, winters in lower 48 U.S. states
Physical Differences
While the red-breasted and common mergansers appear somewhat similar, there are some key physical differences between them:
Size
The common merganser is slightly larger than the red-breasted merganser. Common mergansers reach lengths of 23-28 inches compared to 22-25 inches for red-breasted mergansers. They also have a slightly broader wingspan at 30-35 inches across, versus 30-36 inches for red-breasted. Common mergansers weigh 2.1-3.6 pounds on average while red-breasted weigh between 1.5-2.4 pounds.
Bill
Both species have long, narrow serrated bills used for grasping slippery fish. However, the common merganser’s bill tends to be straighter and heavier than the slender, tapered bill of the red-breasted merganser.
Color Patterns
The most striking difference between these two mergansers is the male breeding plumage. Male red-breasted mergansers have a bright rusty red breast, green head, and distinctive white neck ring. Male common mergansers have a solid green head and white neck and body. Females of both species are difficult to distinguish, having gray-brown heads and bodies. The common merganser female may be slightly paler overall.
Range and Distribution
While their breeding ranges overlap in Canada and Alaska, red-breasted mergansers winter primarily along the Pacific, Gulf and Atlantic coasts while common mergansers can be found throughout the lower 48 United States in winter. The red-breasted merganser’s more limited winter range may be related to its smaller body size and narrower temperature tolerance.
Behavioral Differences
In addition to physical differences, these two merganser species exhibit some subtly different behaviors, particularly during the breeding season:
Courtship Displays
Male mergansers perform elaborate courtship displays for females that include head bobbing, wing flapping, and calling. Common mergansers tend to hold their necks straight out and shake their heads during display, while red-breasted mergansers throw their heads back further.
Nest Sites
Red-breasted mergansers often nest in tree cavities, rock crevices, or nest boxes, while common mergansers typically nest on the ground among dense vegetation near water. The red-breasted merganser’s preference for nest cavities is thought to be related to the fact that it inhabits colder regions where elevated nest sites offer better insulation.
Brood Behavior
Common merganser ducklings leave the nest within a day after hatching and are led by the female parent to water where they swim and feed. Red-breasted mergansers, however, carry their young on their backs to water, sometimes several miles over land from the nest site. The red-breasted ducklings may ride on the mother’s back for their first 2-3 weeks until they learn to feed and swim independently.
Migration Timing
The common merganser is one of the earliest diving ducks to migrate north in spring, as it nests on land and so moves when ice melts on lakes and rivers. The red-breasted merganser nests later, since it utilizes tree cavities, and so migrates north later in spring compared to other ducks. In fall, red-breasted mergansers migrate south earlier than common mergansers as well.
Habitat Preferences
The merganser species inhabit similar aquatic environments but have some differing habitat inclinations:
Freshwater vs. Saltwater
While both species live largely on freshwater lakes, rivers and ponds in summer, red-breasted mergansers tend to prefer saltwater habitats like estuaries and coastlines in winter. Common mergansers can be found on fresh and saltwater through their full range.
Small Streams vs. Large Lakes
During the breeding season, red-breasted mergansers favor smaller, fast-flowing streams and rivers as they provide abundant small fish prey. Common mergansers nest more often on larger lakes and broad slow-moving rivers where they forage on larger fish.
Forest Lakes vs. Open Water
Since they utilize tree cavities for nesting, red-breasted mergansers are often found on small forest-lined lakes and ponds. Common mergansers use more open waterways and wetlands with shoreline vegetation.
Coastal Islands vs. Inland Wetlands
In winter and migration, red-breasted mergansers congregate in large rafts on protected coastal bays, sounds, and nearshore islands. The common merganser occurs both coastally and further inland on lakes, rivers and reservoirs throughout its winter range.
Diet and Foraging Differences
As fish-eating specialists, mergansers have similar diets but some variation in their prey preferences:
Fish Size
Red-breasted mergansers tend to target smaller fish from 3-8 inches long such as stickleback, minnows, and juveniles of larger species. The larger common merganser can handle fish up to 12 inches including larger perch, sunfish, and trout.
Fish Type
The most common fish consumed by red-breasted mergansers include stickleback, sculpin, trout, and salmon. For common mergansers, sunfish, bass, suckers, and catfish are more regularly eaten along with a wider variety of species.
Foraging Strategy
To hunt, red-breasted mergansers swim rapidly alongshore or over reefs stirring up small fish. The common merganser is more likely to float slowly across open water watching for large fish to pursue. Their differing bill shapes may complement their typical prey sizes.
Diet Composition
Prey Type | Red-Breasted Merganser | Common Merganser |
---|---|---|
Fish | 90% | 80% |
Aquatic Insects | 5% | 10% |
Crustaceans | 3% | 5% |
Mollusks | 2% | 3% |
Other | 1% | 2% |
While fish make up the majority of their diets, red-breasted mergansers eat a slightly higher proportion of fish versus crustaceans and insects taken by common mergansers. This likely reflects their preference for small streams where fish are more abundant than other aquatic fauna.
Breeding and Reproduction
Red-breasted and common mergansers follow similar breeding patterns overall but with some key differences:
Courtship and Pairing
Courtship begins in late winter or early spring, but common mergansers pair up earlier – typically in February-March, while red-breasted mergansers don’t settle into pairs until April or May. Their elaborate courtship displays help form pair bonds.
Nest Sites
As mentioned earlier, common mergansers nest on the ground concealed by shoreline vegetation while red-breasted mergansers use elevated nest cavities more often. However, female red-breasted mergansers may also make ground nests at times, in which case they line the nest with down feathers plucked from their own breasts.
Clutch Size
Species | Average Clutch Size | Egg Color |
---|---|---|
Red-breasted Merganser | 8-11 eggs | Pale cream |
Common Merganser | 9-13 eggs | White |
Common mergansers lay slightly larger clutches on average compared to red-breasted mergansers. Egg color also differs between the species.
Incubation and Fledging
Only female mergansers incubate the eggs for about 28-35 days. Merganser ducklings leave the nest within 24 hours of hatching. They fledge at around 70 days old for red-breasted and 60 days for common mergansers.
Duckling Care
As noted earlier, after hatching red-breasted merganser ducklings may be carried over land on the mother’s back before swimming independently. Common merganser ducklings immediately follow their mother to water after leaving the nest.
Population and Conservation
Both merganser species have thriving populations across North America:
Population Status
Species | Population Estimate | Population Trend |
---|---|---|
Red-breasted Merganser | 350,000 | Stable |
Common Merganser | 650,000 | Increasing |
Common mergansers greatly outnumber red-breasted mergansers over most of their shared range. Both species were negatively impacted by hunting and habitat loss historically, but have rebounded well under improved protections.
Threats and Conservation Status
Neither merganser is under serious threat currently. Their habitat needs are generally protected and they remain common game species with regulated hunting seasons. Both are classified as “Least Concern” on the IUCN Red List of threatened species.
Causes of Mortality
Natural causes of merganser deaths include predation, disease, severe weather, and starvation during extreme cold conditions. Human-related mortality includes hunting, lead poisoning from fishing gear ingestion, boating collisions, and oil spills. Proper management practices help minimize excessive human-related losses.
Conclusion
In summary, the red-breasted and common mergansers exhibit many similarities as fish-eating diving ducks occupying North American waterways. However, important differences in their size, coloration, bill shape, habitat and dietary preferences, nesting behaviors, and winter distributions help distinguish these two species. While the red-breasted merganser prefers smaller fish in fast-moving streams and nests in cavities, the larger common merganser feeds more on large lake fish and nests on the ground. Both play vital roles as predators and prey in aquatic food chains across the continent. With sound conservation practices, these two mergansers will continue thriving and amazing birdwatchers for generations to come.