How to identify the Red-breasted Merganser

To correctly identify the Red-breasted Merganser (Mergus serrator), check each of these features. Birds can be tricky: habit, habitat, and call often confirm a sighting that a single photo cannot.

Size at a glance

Length

51-62 cm (20-24 in)

Wingspan

70-86 cm (28-34 in)

Weight

700-1350 g (1.5-3.0 lbs)

Physical features to check

1. 1

   Plumage

   Overall feather coloration and pattern.

   Adult breeding male: Dark iridescent green head with a shaggy double crest, white neck collar, rusty-red breast streaked with black, white flanks finely vermiculated with black, black back, and a prominent white patch on the inner wing (speculum) visible in flight and at rest. Adult female: Reddish-brown head with a shaggy crest, white chin and throat, grayish body plumage, and a white wing patch. Non-breeding male (eclipse plumage): Resembles the female but often retains some darker back feathers and a more defined white wing patch.

2. 2

   Beak shape

   Shape and color of the bill: a key field mark.

   Long, slender, and pointed bill with serrated edges (lamellae) for gripping fish. Bill color is red in adults, duller orange-red in immatures.

3. 3

   Eye color

   Iris color and any distinctive eye markings.

   Red in adult males, reddish-brown in adult females and immatures.

4. 4

   Leg color

   Leg and foot color.

   Bright orange-red in adults, duller orange in immatures.

5. 5

   Distinguishing features

   Standout features that separate this species.

   Shaggy crest on both sexes, slender serrated bill, and the distinctive rusty-red breast band on breeding males. The white wing patch (speculum) is a key field mark for both sexes.

6. 6

   Juvenile appearance

   How young birds differ from adults.

   Juveniles resemble adult females but have a shorter, less shaggy crest, duller bill and leg coloration, and often a more mottled appearance to their body plumage.

7. 7

   Seasonal changes

   Plumage variation between breeding and non-breeding seasons.

   Males undergo an eclipse plumage in late summer/early autumn, resembling females but often retaining some darker back feathers and a more distinct white wing patch. They regain their breeding plumage by late autumn/early winter.

8. 8

   Sexual dimorphism

   How males and females differ.

   Pronounced sexual dimorphism in breeding plumage, with males being much more brightly colored and patterned than females. Females are generally duller brown and gray.

Key field marks

• Crest. Look for the shaggy, often messy-looking crest on the back of the head in both sexes. It's more pronounced in males.
• Bill Shape and Color. Observe the long, slender, pointed, and serrated red bill. This is a key feature distinguishing mergansers from other ducks.
• Male Breeding Plumage. Identify the iridescent dark green head, white neck collar, and the rusty-red breast band streaked with black. The white flanks with fine black vermiculations are also distinctive.
• Female/Immature Plumage. Note the reddish-brown head with a shaggy crest, contrasting with a paler throat/chin, and a grayish body. The white wing patch is still visible.
• White Wing Patch (Speculum). Look for a prominent white patch on the inner wing, visible both in flight and when the bird is at rest on the water. This is present in both sexes and all plumages.
• Behavior. Watch for their characteristic diving behavior to catch fish. They often swim low in the water.

Explore the Red-breasted Merganser