There are lots of examples of birds looking like other things in order to avoid or frighten away predators. Many nightjars (Order Caprimulgiformes) look like leaf litter, bark or leaves. The Brown Creeper blends in with the tree trunks it climbs. The winter plumage Willow Ptarmigan is all white to blend into their snowy landscape. The Sunbittern, when frightened, spreads its wings to display its eye-like markings as if it were a fierce giant. The indigo birds and whydahs of Africa are nest parasites; their young imitate the gape pattern of the young of the hosts in order to be fed.
TOP: The image shows a cinereous mourner nestling (Laniocera hypopyrra).
BOTTOM: Shows a large, hairy caterpillar from the area that matches the nestling’s plumage characteristics.
But one of the most interesting, unusual, and evolutionarily sophisticated is that of the newly hatched chick of the Cinereous Mourner, Laniocera hypopyrra, a resident of northern South America, which mimics the appearance and behavior of a poisonous caterpillar, the larva of the flannel moth, to avoid being eaten by snakes and monkeys. Not only do the hatchling birds look like the spiny caterpillars but they move like them in an undulating motion.
Flannel moth larvae are protected by poisonous spines concealed beneath their conspicuous long, fine hairs. These spinous hairs cause a nettling (like nettles) sensation on contact with the skin. Some moth species cause particularly severe reactions and are hazards for plantation workers in parts of South America.
Whether predators are deterred by the look of the larval-appearing young is unknown, but it seems likely. This appears to be an example of Batesian mimicry in which the mimic looks like the dangerous or poisonous species but does not have those characteristics itself. Perhaps the most well-known example is that of the monarch and viceroy butterflies. The monarch is distasteful to predators which learn to avoid it. The viceroy is very similar but is perfectly edible. It looks enough like the monarch to be avoided and thus gains protection without actually being distasteful.
How does mimicry come to be? As an example, suppose an insect species, for no particular reason, contains a chemical that is distasteful to any animal that tries to eat it. Like most biological characteristics, there is a continuum. Some insects of this species might contain more of the chemical or a more concentrated version, for example. The more of these most toxic individuals in the population, the more predators encounter them and the faster they learn. So natural selection encourages the proliferation of distasteful individuals.
Palatable species that have no defensive chemicals but benefit by looking like a dangerous species, so evolution crafts them, the mimics, to look even more like the model. What’s unusual about the Cinerous Mourner is that it is a bird mimicking an insect – a nestling bird imitating a larval insect! What will we discover next?