The chicks of an Amazonian bird species have evolved a clever trick to avoid being eaten by predators, researchers say; they mimic the coloring and movements of a toxic caterpillar.

Nesting chicks of the cinerous mourner, Laniocera hypopyrra, are hatched covered in long downy feathers of a bright orange hue that matches the coloration of a large, hairy and poisonous caterpillar also found in the same region of southeastern Peru.

The hatchlings have also been observed moving their heads slowly from side to side in the nest, a movement typical of many species of hairy caterpillars, the researchers report in the journal The American Naturalist.

It's an example, they say -- rare in vertebrates -- of something called Batesian mimicry, named for English naturalist Henry Walter Bates who conducted research in the rainforests of Brazil.

In Batesian mimicry, a harmless but vulnerable species evolves to imitate the warning signals or appearance of a harmful species that's directed at a common predator.

By mimicking the true warning signal of the protected species, the Batesian species can gain the same advantage against predators even though it does not possess an actual protecting quality such as a poison.

Researchers Gustavo A. Londoño, Manuel Sánchez Martínez and Duván Garcia described the unusual nesting strategy in the lowland bird species that inhabits an area around tropical Peru's Madre de Dios River that normally experiences very high losses of chicks to nest predators.

Nest predation at a high rate is common in most tropical habitats, they say.

However, with its matching orange garb and caterpillar-like movements, cinerous mourner chicks seem able to trick predators into thinking they're a toxic, spiny and inedible caterpillar instead of a tasty nestling, the researchers say.

The researchers made their discovery in 2012, finding only the second cinerous mourner nest ever discovered, and after observing the unusual coloration and behavior of the chick, they subsequently found the poisonous caterpillar living in the same area with similar size and hair coloration as the nestling.

The remarkable mimicry may have evolved especially to decrease the probability of nest predation to improve the reproductive success of the species, the researchers suggest.