The Caterpillar Defense

Let’s say you’re a baby bird. In particular, you’re a chick belonging to the species Laniocera hypopyrra, which also goes by the elegant common name of the cinereous mourner. You hatch out of your egg and find yourself in a nest up in tree in a rain forest in Peru. You can’t fly. You can only wait for your parents to bring you food. You are, in other words, easy pickings.

So what might you do to avoid getting snatched up by a predator? Perhaps you might hold very still so as not to attract attention. Perhaps you might also grow dull, bark-colored feathers to help you blend into you background.

If you’re a cinereous mourner, however, this is not what you do. As you can see in this video, you grow brilliant orange plumage. You make yourself absurdly easy to see.

In 2012, a team of scientists first pointed out how odd it was that cinereous mourner chicks were so bright. Weirder still, the chicks become drab as they grow up. The researchers based their study solely on museum specimens of the bird, so they couldn’t learn all that much about what it’s like to be a bright orange chick in a predator-rife jungle. But they proposed that the chicks were actually ensuring their safety by growing bright feathers. They might be poisonous, for example, with toxic chemicals in their feathers. Their bright colors were thus a warning. Or perhaps they were harmless, but they were mimicking some unknown animal that was harmful.

Now Gustavo A. Londoño of the University of California at Riverside and his colleagues have observed cinereous mourner chicks in the wild. They’re the ones who filmed the footage above. They were struck by the way that the chicks creep around their nests, like a caterpillar. Not just any caterpillar mind you. Like this one:

This bizarre caterpillar, which lives near cinereous mourner nests  is enormous. It’s 12 centimeters long, or about the size of a cinereous mourner chick. And its hairs are tipped with an irritating toxin. Londoño and his colleagues propose that the chicks both behave and look like this caterpillar (which belongs to a yet-to-be-described species).

The resemblance goes beyond just color, Londoño observes. The chicks grow unusual feathers with long white tips–which resemble the hairs of the caterpillars, as shown in this figure.

Londoño argues that cinereous mourner chicks practice something called Batesian mimicry. It’s a strategy that scientists have found in many species, especially butterflies. But this is the first time anyone’s found a possible case of Batesian mimicry in a bird. It’s possible that the cinereous mourner chicks were driven to evolve this unusual strategy because they’re especially vulnerable. Londoño and his colleagues have found that predators kill off chicks in at least eighty percent of nests, possibly because the parents don’t guard them enough. Under such extreme risk, the chicks have evolved an extreme solution.