Cinereous Mourner
Image credit: Santiago David Rivera

The cinereous mourner is a bird found in subtropical or tropical moist lowland forests of South America. In an area that has a high number of nest predators this remarkable bird has evolved a strategy that makes it highly unattractive to potential aggressors such as mammals, snakes and other birds.

In a study published in The American Naturalist Gustavo A. Londoño, Duván Garcia, and Manuel Sánchez Martínez reported that in the autumn of 2012 while they were working on a long-term avian ecological project, they discovered only the second nest ever described of the chinerous mourner at Pantiacolla Lodge in the upper Madre de Dios River in southeastern Peru.

The team observed that when they hatched, the chicks had downy feathers with long orange barbs with white tips and looked very different from any other nestlings they had observed in the area.

Although the strange down feathers attracted their attention it was the nestling’s behaviour that the researchers found more interesting. As they began to collect measurements of the chick it started to move its head slowly from side to side in the manner of many hairy caterpillars.

While working in the same area, the team also found a poisonous caterpillar of similar size and hair colouration as the cinereous mourner nestling.

The team believed they had stumbled across an example of Batesian mimicry.

Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of harmful species. One of the most famous examples of Batesian mimicry is that of the viceroy butterfly, a harmless butterfly that has evolved to mimic the monarch butterfly which is poisonous and uses its orange colouration as warning to potential predators.

The adaption of the cinereous mourner to trick potential predators into thinking it is a toxic, spiny caterpillar, is a very rare example of Batesian mimicry in vertebrates and thought to be the first observation of a bird mimicking a caterpillar.

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