Tricking predators to save their skin
Figure 1: Blending in
I recently watched the DVD of Robert Redford and Paul Newman in ‘The Sting’, and was amazed yet again at the complicated plan and its implementation, involving many people and major props, that was used to trick and relieve a mob boss of his money. We are not the only species on the planet that uses trickery to out manoeuvre our opponents. The animal world is full of tricksters that use deception to outwit others. The world of nature is full of animals eating another or being eaten. Prey species use a range of tricks to avoid being caught by predators; while predators, in turn, deceive prey species by various means.
The simplest means of avoiding being eaten or avoiding spooking their prey is to not be seen. Countershading is a means of looking like the background. In the ocean, an animal’s back is often darker than its belly. When viewed from above (the sky) the colour of the animal’s back blends in with the colour of the ocean depth, which is what is seen from above; while viewed from underneath, the lighter belly blends in with the lighter sky. Sharks, dolphins and many fish exhibit countershading. Some animals adopt the colour of their environment and disguise themselves by truly blending in with the background.
This is called camouflage or cryptic colouration. Ptarmigans — birds of the arctic region — are brown during the summer, looking like the ground on which they walk. By winter, their plumage is pure white, matching the snow on the ground. In Sri Lanka, frogmouths and nightjar are both speckled brown and blend in with the environment: the former blending with the brown of the branches of trees and the latter, blending in with the ground and leaf litter. (figure 1) Ptarmigans moult their feathers at the end of summer and grow new white feathers for the winter to camouflage themselves.
Figure 2: Warning colouration
But cuttlefish, squid and octopuses change the colour of their skins in the blink of an eye to blend in with their environments. They achieve these amazing transformations using thousands of colour-changing cells called chromatophores that lie just below the surface of the skin. Within each chromatophore is an elastic sac-like balloon, full of variously coloured pigments. The nervous system of these animals controls these sacs, expanding and contracting them to make one colour visible or not. These quick-change artists are therefore able to avoid predators. Other animals do not just change the colour of their skins or feathers, but have evolved to look like the environments in which they live.
Stick insects and leaf insects of Southeast Asia look, as their names suggest, like sticks and leaves. The former have cylindrical stick-like brown bodies, and the latter, flattened, green and leaf-like bodies. Other species such as the dresser or decorator crab disguise themselves by decorating themselves with bits of coral or seaweed and then freezing when a predator passes by. The shells have Velcro-like hairs onto which they place objects from the environment. Another form of camouflage is disruptive colouration, which breaks up the shape and obliterates the outline of an object, impeding detection. This is exhibited by both predators and prey. Spots and stripes serve to break up the outline.
Examples include the stripes of zebras and tigers and the spots of leopards. The black stripes and spots of tigers and leopards respectively, blend in with shadows and the background colour of the fur with the environment in which they live. In the case of the zebra, not only are the stripes in an individual confusing, but when a herd is together, it is very difficult for the predator to focus on a single animal to kill. The opposite is true in animals that show warning colouration or aposematism. In this case, animals clearly advertise that they are dangerous. Classic warning colours of the animal kingdom are red, orange, yellow, black and white contrasted with each other, or as very prominent markings.
Poison arrow frogs of South America flaunt bright yellows, reds, oranges and blue to warn predators that they are toxic. In Sri Lanka, the Crimson Rose, a large swallowtail butterfly with striking black, white and crimson markings, is telling predators that it is unpalatable or toxic. (Figure 2) Yet another method of avoiding predators is to look like — or mimic — a poisonous species. This is called Batesian mimicry after a 19th century British scientist called Walter Bates who studied this type of mimicry in the Amazon. The mimic is harmless, but the model is poisonous. In Sri Lanka, the harmless Common Rose butterfly mimics the poisonous Crimson Rose; the non-toxic Sri Lankan wolf snake mimics the highly venomous Sri Lankan krait.
In contrast, Müllerian mimicry (named after the German zoologist Fritz Müller) occurs when two (or more) distasteful or poisonous organisms resemble each other. Both species benefit because a predator who learns to avoid one species will most likely avoid the other, too. The poison arrow frogs of South America are good examples of Müllerian mimicry. Yet another form of mimicry is aggressive mimicry where a predator mimics harmless species — the classic ‘wolf in sheep’s clothing’. The blue-striped cleaner wrasse is a small fish that lives among coral reefs, and ‘cleans’ parasites and dead skin off larger fish, in return for scraps of food. The blue-striped fangblenny or sabretooth blenny mimics the cleaner wrasse but instead of cleaning larger fish, takes chunks of flesh off the hapless victim waiting to be cleaned.
Some animals do not use colour or shape to throw off predators, but instead change their behaviour. ‘Playing ‘possum’ is a phrase used commonly to mean feigning death and remaining still to escape attention or remain undetected. This phrase is derived from the behaviour of the Virigina opossum, which reacts to threats by pretending to be dead. Other species use distraction displays to divert a predator away from a nest of young. Birds of the lapwing family are known to fake having a wing that is broken and limp away from the nest drawing the predator away. Plovers pretend to be brooding their nest, when in fact, they are sitting on nothing, away from the nest, and then fly away quickly when the predator nears. Yet other species use deimatic behaviour to startle or threaten predators.
Figure 3 : Deimatic behaviour
The classic examples the spots of a butterfly’s wings — such as those of the Gladeye bushbrown that is found in Sri Lanka — which has large eye-like spots on it wing which it unfurls, startling a predator. The most dramatic example of deimatic behaviour is shown by the Australian frilled lizard. Looking like a drab brown, normal lizard, this lizard rears up when threatened, opens its mouth (which is a startling yellow), and unfolds a pleated skin flap around its head like a frill and hisses. (Figure 3) However, the most amazing mimic and a master of disguise, is Indonesia’s mimic octopus, which not only can change colour but is a master shape-shifter. It is the only animal known that can physically mimic more than one model, looking at different times like a lion fish, flatfish, jellyfish or sea snake.
Mimicry is not only confined to confusing the sense of sight. Other senses such as hearing are also targeted. Tufted capuchins found in South America live in hierarchical troops where older animals are more dominant and have first access to food. Subordinate tufted capuchins are known to make false alarm calls (which are normally used to warn of an approaching predator) to distract the dominant capuchin, so that they can pinch the food. Our white-bellied and greater racquet-tailed drongos are good mimics of other bird calls, confusing not only other animals but also bird watcher beginners. The striking lyre birds of Australia, with their long lyre-like tail feathers, are, however the masters of vocal mimicry, not to hide from predators/prey or distract others, but to attract mates.
Like professional tenors who sing arias from Puccini, Bizet, Verdi and Wagner, these birds also have wide repertoires: mimicking not only the calls of some twenty different birds but also anything they hear in their environment: such as barking dogs, car alarms, camera shutters and even chainsaws and trees falling. The reader is referred to <https://www.youtube.com/watch?v=VjE0Kdfos4Y> to hear this amazing bird. During the breeding season, lyre birds sing for as long as four hours a day! The animals mentioned above have acquired their various adaptations through millions of years of evolution.
However, humans, in a short space of a few centuries, are laying waste to many of them. Poison arrow frogs are threatened with habitat loss; while another species of ptarmigan (the white-tailed ptarmigan) is affected by habitat fragmentation as a consequence of climate change; sharks are overexploited for their fins for use in shark fin soup; and the mimic octopus is being over-collected for aquaria. To paraphrase American writer Stewart Brand, we humans have the moral obligation and the ability to repair at least some of the damage we have wreaked on the Earth.