Amazonian bird may act the part of its hairy caterpillar disguise

Rare images show how baby cinereous mourner deceives potential predators

baby cinereous mourner

DELICIOUS BIRD OR POISONOUS CATERPILLAR? A rare look at a baby cinereous mourner suggests the birds' nestlings imitate toxic hairy caterpillars to discourage predators.

Santiago David-Rivera

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The orange chick of an Amazonian bird looks a lot like a toxic caterpillar. Now a rare peek into a nest suggests the chick may act the part, too.

Adults of the bird called the cinereous mourner (Laniocera hypopyrra) are gray with a few brownish spots on the shoulders. “Boring,” acknowledges Gustavo Londoño of Universidad Icesi in Cali, Colombia. Yet the chicks, which are frail and reside in leafy nests that look like open cups, boast vivid, attention-grabbing color. A recent survey suggests that some 80 percent of cup nests in the region get attacked, Londoño says.

The chicks’ appearance, however, may discourage predators. A 1982 paper proposed that fluff disguises chicks as less desirable moss-covered fruits. And in 2012, another team proposed that chicks might resemble toxic orange caterpillars from the region — at least as far as the researchers could tell by examining two museum specimens of baby mourners.

Watching and photographing a live chick in a cup nest in Peru supports that idea, Londoño and his colleagues report in the January American Naturalist. In addition to sporting a caterpillar-esque coat, the chick waved its head from side to side when the nest was disturbed. That’s peculiar for a baby bird, but it’s a very caterpillar thing to do.

These nest observations are only the second published for the cinereous mourner, and they fit with the proposal that mourners exhibit Batesian mimicry. In this classic evolutionary bit of fakery, never before seen in bird nestlings, vulnerable organisms increase their chances of survival by imitating dangerous or inedible neighbors.

The South American cinereous mourner may have evolved so that its nestlings look like this toxic orange caterpillar. Wendy Valencia
A four-day-old cinereous mourner, shown in a nest next to an egg, resembles a fuzzy toxic caterpillar. DuvÁn A. GarcÍa
By 14 days old, the disguised chick is developing dark wing feathers. Santiago David-Rivera

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