They Whistle, But Are They Ducks?

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A white-faced whistling duck poses for the camera.

White-faced whistling duck. Most. Outlandish. Duck. Ever!

Found at the San Diego Zoo in both of our flamingo exhibits, its wild range includes most of Sub-Saharan Africa and much of South America. Named for its high-pitched whistling call, this mottled-brown bird with a chestnut breast, black neck, and white face looks like a duck but doesn’t act like one!

White-faced whistling ducks have a number of odd traits for a duck:
1) Both the male and the female look identical.
2) The male actually helps to raise the young!
3) The male and female preen each other.

Think of a typical duck. You may have chosen a mallard, pintail, wood duck, or a harlequin. For all of those species, the male is flashy to attract the females’ attention, and the female is usually drab to allow her to hide when she is sitting on her nest. This trait is called sexual dimorphism: the male looks different from the female. White-faced whistling ducks are sexually monomorphic: the male looks identical to the female! Why are most ducks dimorphic while a few are monomorphic?

Ducks that are dimorphic are typically monogamous for just one breeding season. The next season, the male has to impress a different female. Hence, he has developed colors that possibly leave him more vulnerable to predation, but they give him a better chance to mate. On the other hand, whistling ducks are monogamous for many seasons. If the male stays with one mate his whole life, he may only have to impress that one female! This means bright, beautiful plumage may not be the best way for him to pass on his genes.

The male whistling duck tries a fairly extreme strategy…he helps to raise his young! A whistling duck dad may not help to incubate the eggs, but he is there for his ducklings’ first swimming lesson. He helps his mate teach their little ones how to eat, how to avoid predators, and helps protect them as they grow up.

Since the males don’t go around impressing the females with their flashy feathers, and the females don’t offer the males the “high-gain/low-cost” benefit of raising the offspring by herself, some activity must bond them to each other during the nonbreeding season. Mutual grooming is one of those activities. Mutual grooming doesn’t happen all that often in the bird world. This behavior is rare enough that it is given a special term: allopreening. Parrots frequently do this, but most other bird species don’t, especially ducks. I don’t want to anthropomorphize, but seeing a duck with her eyes closed, head tilted to the side so her mate can preen her cheeks leads me to the conclusion that she enjoys her mate’s company.

They don’t act like a typical duck, do they? Well, white-faced whistling ducks are a part of the Anatidae family, which includes geese, swans, and all ducks. However, unlike mallards, black ducks, and gadwalls, which belong to the Anatinae subfamily, the white-faced whistling ducks belong to the Anserinae subfamily, which includes swans and geese. This may seem like trivial evolutionary mumbo-jumbo, but it so thoroughly explains the odd behavior whistling ducks exhibit. Their evolutionary history suggests their behavior may not be all that odd. Think of a typical goose. Most likely it’s:

1) Sexually monomorphic.
2) The male helps raise the young.
3) The pair allopreens.

Sounds like the behavior of a whistling duck to me! We can learn a lot from these humble birds. We may expect them to act a certain way because of how they look, but we can know a lot more about them if we just take the time to learn their history.

Mike Grue is a senior keeper at the San Diego Zoo. Read his previous post, Pochards and Ruddy Ducks Break Rules.