Red-breasted Merganser

How to find it

Finding one here means being in the right place by luck, since there is no regular site for it. Look closely at any odd duck on open water, especially in winter and around coastal lagoons and river mouths. A long, thin red bill and a shaggy crest are the first things to note. A slim bird that dives repeatedly fits a merganser. Any sighting deserves careful notes and photos, because the other merganser on the Costa Rican list is also an extreme rarity.

How to recognise it

This is a large, slim diving duck, 51 to 64 cm long. Its long, thin bill has saw-like edges that help it hold slippery fish.

Breeding males show a dark green head with a shaggy, double-pointed crest, a white collar, a rusty breast flecked with black, gray sides, red eyes and a thin red bill.

Females and young birds are grayish brown with a cinnamon-brown head and a wispy crest. The head blends gradually into a dingy breast, and the throat patch is indistinct.

These descriptions come from the species across its range, not from Costa Rican birds specifically.

What it sounds like

Recording: Corvi Zeman, CC BY 4.0, source, read 4 Nov 2026.

Behaviour and diet

It dives from the surface and chases aquatic prey underwater, and it hunts by sight, diving up to about 4 meters. Fish are its most frequent prey, though it also takes aquatic insects, crustaceans and frogs. A skilled diver, it usually runs across the water surface to take off. Once airborne it can fly low and almost silently over the water at considerable speed. Some guides list it among the fastest ducks, and one bird reached about 100 mph while an airplane chased it. These habits are described for the species across its range.

Where it lives

Outside Costa Rica, this duck breeds on northern lakes and rivers and then migrates to the coast. It winters mostly on coasts and uses saltwater more often than any other merganser. In coastal areas it is often seen at river mouths, which fits the lagoon-and-coast setting of the Costa Rican record on the Caribbean side near Limón. In Costa Rica it is accidental, so it has no home range or elevation band of its own here.

When to see it

Winter is the likeliest time for a stray. A Costa Rican birder noted that northern cold fronts in December and January can bring unusual birds, and he suspected one brought a merganser to Panama in late 2021. The first Costa Rican record dates to spring 2020, shortly before pandemic closures began.

Similar birds

Common Merganser is the closest look-alike. The male Common has a smooth head with no crest, a white breast and brown eyes, while the Red-breasted male has a crest, a reddish breast and red eyes. Females are harder: the Red-breasted has a thinner bill, a slimmer neck and a thin crest that often forms two tufts, and it lacks the Common's sharply defined white chin. The Hooded Merganser, the other merganser on the Costa Rican list, is a smaller duck. A female Hooded was found at Lake Arenal near Nuevo Arenal in 2020, around the same time as the Red-breasted.

Names and lore in Costa Rica

The official Costa Rican Spanish name is Serreta Pechirrojo. Elsewhere in Spanish this duck is also called serreta mediana, mergo copetón, pato serrucho and mergansa pechirroja; these are general Spanish names, not Costa Rican nicknames.

Status and conservation

The AOCR list (updated June 2026) marks it A, accidental, so it is a very rare vagrant in Costa Rica, while worldwide it is rated Least Concern.

Photography tips

Look for a slim, low-riding duck that dives repeatedly, then photograph the head and bill in profile. Capture the crest shape, the eye colour and the breast, since these separate it from Common Merganser. A shot of the white chin area also helps with females.