Seeing red-breasted mergansers, a species of duck that flocks to Orange County this time of year, will likely require a trip to the coast. The species famously prefers the near-shore ocean and bays to inland waterways when it isn’t breeding.

Oddly, this species of merganser – the males easiest to recognize with their dark, crested heads – doesn’t mind freshwater when it’s on its breeding grounds up north in Canada and Alaska.

Meanwhile, a related species, the common merganser, seems to have the opposite preference. When it isn’t breeding, it is more likely to be found inland.

It might be a case of an evolutionary phenomenon called “habitat partitioning.” Closely related species sometimes adapt to different habitats to reduce competition.

Red-breasted mergansers are a little unusual in the food-preference department as well. This diving duck is among the few duck species that hunt for fish.

The ducks are excellent swimmers, remaining submerged for some time.

The more colorful males are a minority compared to the more drab females.
Look for them at the Bolsa Chica wetlands. They might also be seen, though in smaller numbers, at Upper Newport Bay.

Scientific name: Mergus serrator
Sources: Biologist Douglas R. Willick; “The Birds of Orange County, California: Status and Distribution,” by Robert A. Hamilton and Douglas R. Willick; “The Sibley Guide to Birds,” by David Allen Sibley.
Illustration by: Brian Moore
Next week: Bed bugs

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