What should a caterpillar look like? A twig! What should a young mammal disguise itself as? The undergrowth in which it hides. This kind of masquerade is a style of camouflage that can be distinct from the more studied cryptic colorations. The act of discovery, as far as a predator (or even prey) is concerned, is of an inanimate object, not the juicy venison or insect steak that is actually readily available. This is a review of camouflage as it is being investigated in various researches.
In one study, birds were used to detect how successful caterpillars were at masquerading. Some domestic chicks tried in an experiment to determine if experience with wooden twigs influenced their attack on caterpillars of 2 species (Early Thorn and Brimstone) of
Twiggy caterpillars. The use of a white background made sure that in these cases cryptic colour could not influence the predator. The action of the birds involved a cognitive process where inanimate objects became associated with the masquerading caterpillar. The question remains on how the predator learns to discriminate between model and mimicking caterpillar. An alternative question was how well suited the prey is to its model. Many insects such as the moths below change their colours and appearance depending on which plant they live. Such variation is the source of evolution. Speciation has obviously been encouraged as they become increasingly isolated on their individual tree species.
Disruptive coloration at parts of the body makes prey less easy to detect. Survival of these animals is higher than those without disruptive colours. Their outline is broken up but can the predator detect the prey outline and is it misled by false edges that occur on some caterpillars? The speed of discrimination might help to determine how learning takes place in the predator
John Skelhorn and Candy Rowe of Newcastle University (UK) publish their paper in the Proceedings of the Royal Society B under the title
Cognition and the evolution of camouflage today.
Anti-predator defence by means of camouflage is reviewed in the schoolboys favourite evolver, the peppered moth, Biston betularia, the same species resembling birch twigs and willow twigs, depending on where it is found while the brimstone, Opisthograptis luteolata and the early thorn, Selenia dentaria resemble hawthorn and its relatives. The leaf butterfly, Kallima spp. was part of another experiment suggesting that masquerade evolves from cryptic ancestry, either with a large mutation or a gradual
improvement Predation could be the only selective force involved, as cognition seems to involve the avoidance of imperfect masqueraders even though they can’t fool as many predators as the more perfect mimics. Speed of learning by the predator is important, because they take longer to learn when the resemblance to the inedible model is better.
It certainly does not cover only insects and mammals. Here is another camouflage story in which reptiles are investigated for their levels of camouflage, such as in the Tanzanian mountain chameleon in this study from 2013.