This blog post was originally published by Columbia Science Review in November 2013.
Video edited by Alexandra DeCandia. See credits for image sources.
By Alexandra L. DeCandia
You can tell by the way she uses her walk... that something's wrong. Tail outstretched and wings akimbo, the killdeer (Charadrius vociferous) cries aloud, limping along the rocky shore as if unable to fly. She appears injured, pained, and consequently, an easy target for any predators in the vicinity. Walk, squawk, falter. Enemies follow every movement of this pathetic scuttle and trail closely behind. Walk, squawk, falter. They near her position. Walk, squawk, falter. They open their mouths. Walk, squawk – the killdeer flies away. She circles the beach and, once her deceived predators have vanished, returns to her eggs hidden in the rocks.
This distraction display of a devoted plover mother is one example of an anti-predator adaptation in the animal kingdom. Driven by the urge to stay alive and filtered through the finely toothed comb of natural selection, numerous strategies have evolved to protect prey species from voracious foes. While some have adopted fairly common tactics, such as hiding in herds (“dilution of risk”) or mimicking poisonous species (“Batesian mimicry”), others have erred on the side of unique innovation. Cuttlefish, horned lizards, and common potoos all fall into this latter category, and like the thespian killdeer, possess sublimely bizarre means of protection.
Cuttlefish (Sepia officinalis) are masters of visual crypsis. Lacking structures for self-defense (other than a deployable ink sack), these protein-rich invertebrates had to devise means of evading predators without being seen. Their strategy: camouflage. Unlike other organisms that bounce light off their scales (“reflective silvering”) or cover themselves with surrounding corals (“self-decoration”), cuttlefish have evolved the ability to alter their skin color to match any background. Manipulating the muscles surrounding roughly 20 million pigmented chromatophores and corresponding reflective cells, cuttlefish can change their color and pattern faster than any other organism on the planet. Therefore, at the first sight of a predator, cuttlefish immediately vanish, rendering their attackers dumbfounded and hungry.
North American horned lizards (Phrynosoma hernandesi) have a similar effect on their predators. However, their method of evasion is drastically different (and, in my opinion, horrifically traumatizing). When threatened by a potential attacker, these colloquial “horny toads” engage in deimatic displays in an attempt to intimidate their rivals. Puffing out their bodies for increased size, horned lizards resort to autohaemorrhaging if the predator doesn’t back down. A stream of red, noxious hemolymph propels from the corners of their eyes onto the face of their attackers. Stunned, the predator ceases its attack, thereby allotting the horny toad a hasty, albeit bloody, escape.
A far cry from the blood-infused-attack-of-strange employed by the horned lizard, the last anti-predator adaptation is one of peace, tranquility, and arboreal inspiration. Its innovator, the common potoo (Nyctibius griseus), is the elusive singer of the Central and South American night. With its characteristically bugged-out eyes and speckled gray feathers, the potoo is a nocturnal insectivore most at risk of predation during the day. Rather than seeking cover for these resting hours, though, the potoo boldly perches on the conspicuous remains of dead trees. Predators are rampant, but this seemingly easy prey eludes all captors by artfully employing mimesis. Head aloft, eyes closed, every muscle stilled, the potoo spends his day posing as the tree. He does not call, he does not move; he is the master of disguise, and he lives another day.
As is apparent from the above examples, anti-predator adaptations take a variety of forms. Whether an individual hides among a herd, or more dramatically feigns injury, matches its surroundings, ejects blood from its eye sockets, or steadfastly adheres to a tree, it is acting to stay alive. If the adaptation is a success, the animal will pass its genes to the next generation. If it is a failure, the adaptation will disappear. It may seem harsh, but through this process, natural selection produces the incredible diversity of behavior, morphology, and ultimate speciation that makes the study of non-human animals so fascinating, absurd, and, in the case of these prey species and their anti-predator defenses, delightfully bizarre.