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).

Londono et al 2014 American Naturalist
Londono et al 2014 American Naturalist

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.

23 thoughts on “The Caterpillar Defense

  1. Hahaha, this is really cool! I’m learning about mimicry under the larger umbrella of animal behaviour in lecture and it’s interesting to see that research is continuously being done in this field. I do wonder, though, how this has become possible through evolution. Was it a series of lucky mutations that one species was able to find out that another species was unpalatable and then managed to evolve to look like the unpalatable species?

  2. I wish science writers could refrain from modeling articles about complex natural adaptations on Kipling’s “Just So Stories” — How the Leopard Got Its Spots, How the Camel Got Its Hump, How the Baby Chicks Designed Orange Camouflage. No wonder Americans don’t understand evolution.

    [CZ: Batesian mimicry is a well-established fact in many species. I’m writing about a scientific paper presenting evidence for a new case. This is a hypothesis for an adaptation that can be tested. And I’d prefer if you didn’t criticize me in the third person.]

  3. Dear Gina Rex:

    Carl Zimmer can be criticized for SOME of his writings. This article is not one of them! It grabbed attention, made a good point, was educational and was not so long that the reader lost interest. Speaking of adaption, could you please elucidate how the species known as Ginasaurus rex lost its sense of novelty?

  4. Hi Carl. Sorry to be “that guy”, but when mentioning ‘Batesian mimicry’ a second time, you happened to mistype it as ‘Bayesian mimicry’. Perhaps you were studying statistics beforehand? 😉 Once again, sorry to be “that guy”; just don’t want anyone who’s unfamiliar with both terms to end up getting confused after a Google search.

    [CZ: Thanks! I blame autocorrect…]

  5. Eileen — Yes! All variations are caused by mutations in genes from one generation to the next. Yep, mutations are overwhelmingly the main source of variation. Mutations are rare of course, but when it happened in this species, the chicks lived on (natural selection). And their genetic material was passed on, and their offspring continued to pass genes on, and the offspring in turned continued to mutate…..with the trait becoming more distinct, and predominating…

  6. This is fantastic example of the types of exciting natural history phenomena that remain to be discovered. Many props to Gustavo Londoño for doing the hard fieldwork that was required to bring this to light.

  7. Another great article; keep them coming.

    It’s always interesting to see the methods of protection that animals use to prevent predation. But if predators still kill 80% of the chicks, there need to be a few more mutations before this change can be considered very successful in my view. Above 80% is a very high loss rate, as we all recognize, but it is better than 100%!.

  8. I went back and looked again; I would like a better survival rate, but to change both the physical appearance and movement is quite a success. Genetics and evolution are working in a variety of areas in the same subject here. That’s amazing.

  9. If the caterpillar “lives near cinereous mourner nests” and is itself highly unusual in form, does that suggest some sort of co-evolution? Do the caterpillars feed on spills from the nest? Is it fed by parent birds?

    [CZ: Nobody knows. Remember, this is a species without a name yet.]

  10. Yes, sorry, I realized as much. I meant to convey a sense of wonder, not a demand for immediate answers. How cool wouldn’t it be if the caterpillar turned out to be a mimicking brood parasite!

  11. Maybe if I invent a comforter that looks like this caterpillar, ‘morning people’ will learn to leave the rest of us alone!

  12. Very interesting, it amazes me how well nature can adapt given the chance. Hopefully more studies can be done before these wonderful birds potentially loose their natural habitat.

  13. Then there is when selection converts mimicry to an actual defense, as in the recently described Pitohui genus from New Guinea, who have not only evolved the standard black/red toxic flag of mimicry, but the toxins as well…

  14. When I hear about convergent evolution, or mimics I always wonder if there is some sort of bulk gene transfer. Dare I say hybridization?

  15. “..predators kill off chicks in at least eighty percent of nests, possibly because the parents don’t guard them enough.”

    This is not true of all birds, I imagine. Some predators are powerful, sneaky and swoop in when the parents are out feeding. It sounds judgmental to me.

  16. With 80% mortality I would have expected the evolutionary pressure would have been for adults to guard their off-spring more closely, which is a common avian trait already.

  17. Birds spend a lot of time food gathering for their young and themselves; they have to eat to live, so they may not have the luxury of spending more time in the nest, and were forced to rely on other adaptations. That’s just a thought; I don’t know this species habits.

  18. The ‘white egg’ is a fecal sac, the wonderful way that chicks and parents keep the nest clean. but i missed seeing that in the video!

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