Pity the tasty nestlings of the cinereous mourner (Laniocera hypopyrra). One of many birds found in the subtropical lowland forests of South America, the species lives in an area where birds tend to suffer very high losses to nest predators. But the cinereous mourner has a handy trick up its wing. It does a rollicking (rolling, actually) sendup of a toxic, spiny caterpillar (Megalopyge) that also calls the area home (see photo below).
Mimicry in nature takes many forms – bugs that look like leaves, shapeshifting octopuses, seahorses indistinguishable from their coral climes. Whether as a way to hide from predators or to afford a sly way in which to entice prey, camouflage create no shortage of “wow” moments in nature. But the cinereous mourner assumes a particularly clever form of the art known as Batesian mimicry. In this form of biological trickery, the docile organism takes on the characteristics of a threatening or dangerous organism, thereby making itself highly unattractive to prospective predators.
And while this seems like a perfectly reasonable strategy of adaptation, it is one that is very rare in vertebrates, according to a study about the cinereous mourner published in The American Naturalist.
In the study, Gustavo A. Londoño, Duván Garcia, and Manuel Sánchez Martínez report what they found while working on a long-term avian ecological study in the Amazon. They discovered the second nest ever described for the cinereous mourner at Pantiacolla Lodge in the upper Madre de Dios River in southeastern Peru. And in it, they observed chicks with downy feathers with long orange barbs with white tips – no other nestlings in the area looked at all like them.
The unusual feathers caught their eyes, but the chicks’ behavior proved even more intriguing. They observed them moving their heads very slowly from side to side; while working nearby, they discovered a poisonous caterpillar with similar size and hair coloration as the nestling, as well as like movements. Describing the morphological and behavioral similarities between the nestlings and the caterpillars as “astonishing,” the cinereous mourner makes a splendid poster child for the strange and wonderful world of Batesian mimicry.
You can see the cinereous mourner's caterpillar dance in the video below.