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Authors: Robert Trivers
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warning calls by parents are used to frighten warring offspring into separating and fleeing for cover, at which point the parents intervene to prevent further strife. In swallows, males apparently use false alarm calls to guard their paternity. They will give an alarm call when they spot their mate near another male, often causing both birds to dive for cover. Males breeding in colonies almost always give such calls when returning to an empty nest during egg laying (when female copulations outside the pair are frequent and threaten his paternity of the offspring) but not at other times (even swallows do not wish to cry “wolf”). Antelopes have been discovered playing the same trick. After a male has spent a day or two in sexual consort with an adult female, he will give a warning bark if the female seeks to move on, as if signaling that a predator lurks nearby and she should remain with him.
CAMOUFLAGE
Camouflage is so common in nature as almost to escape notice. Most creatures are selected at the very least to blend in to their backgrounds, with stick and leaf insects merely extreme examples. But at the behavioral level, octopuses and squid are so advanced as to be worth special note.
Octopuses and squid are fat, tasty creatures without a protective shell, so they are naturally sought after by a wide range of predators, mostly fish but also mammals and diving birds. Their only defense (beyond ink clouds and biting) is camouflage, and here they have evolved a remarkable system in which each skin-color cell is innervated by a single neuron, thus cutting out all synaptic delays and permitting a near-perfect adjustment to the background in about two seconds. While feeding, the animal can move very slowly across a great range of backgrounds, continuously remaining nearly invisible to others by adjusting its color to each new surface—sand, mud flats, coral reefs, rocks, sea-grass beds, and so on. Octopuses look as if they are slowly rolling while continuously adjusting to what is below. When they want to swim fast, they mimic flounders, in shape, color, swimming movements, and speed, darting swiftly along the sea bottom.
At intermediate speeds (when foraging), they adopt a most unusual strategy of randomly displaying variant phenotypes at about the rate of three per minute, for hours at a time, as if they are shuffling through a deck of cards featuring different camouflaged versions of themselves. This helps prevent the predator from forming a specific search image for any particular version. Just as the predator recognizes potential prey, the prey has morphed into a novel camouflaged form. One species of squid has also evolved a female mimic, one so good that he sometimes fools even fellow female mimics, who approach in search of copulation. This is yet another case of deception being too convincing for its own good.
DEATH AND NEAR-DEATH ACTS
It has long been known in predator/prey relations that deception can work anywhere from first detection until final consumption. Consider two examples near the time of death itself. The feigning of death typically occurs after the prey is caught, and is thought to inhibit the final death-dealing strike. The bird acts dead, lifeless, but remains conscious and alert so that often the only sign of life is its open eyes. Chickens run at the first opportunity, typically when the predator lets go, but a duck threatened by a fox often remains immobile for some time after release, especially if other foxes appear to be present. The fox’s counteradaptations are to kill some prey immediately upon capture and to disable the remaining ones by severing a wing on each.
In the broken-wing display, a bird near its nest tries to distract a potential predator by acting like an injured bird, with one broken and extended wing. The bird moves awkwardly near the predator with wing extended but flies away quickly when attacked. This display is much more dramatic the closer the predator is to
CAMOUFLAGE
Camouflage is so common in nature as almost to escape notice. Most creatures are selected at the very least to blend in to their backgrounds, with stick and leaf insects merely extreme examples. But at the behavioral level, octopuses and squid are so advanced as to be worth special note.
Octopuses and squid are fat, tasty creatures without a protective shell, so they are naturally sought after by a wide range of predators, mostly fish but also mammals and diving birds. Their only defense (beyond ink clouds and biting) is camouflage, and here they have evolved a remarkable system in which each skin-color cell is innervated by a single neuron, thus cutting out all synaptic delays and permitting a near-perfect adjustment to the background in about two seconds. While feeding, the animal can move very slowly across a great range of backgrounds, continuously remaining nearly invisible to others by adjusting its color to each new surface—sand, mud flats, coral reefs, rocks, sea-grass beds, and so on. Octopuses look as if they are slowly rolling while continuously adjusting to what is below. When they want to swim fast, they mimic flounders, in shape, color, swimming movements, and speed, darting swiftly along the sea bottom.
At intermediate speeds (when foraging), they adopt a most unusual strategy of randomly displaying variant phenotypes at about the rate of three per minute, for hours at a time, as if they are shuffling through a deck of cards featuring different camouflaged versions of themselves. This helps prevent the predator from forming a specific search image for any particular version. Just as the predator recognizes potential prey, the prey has morphed into a novel camouflaged form. One species of squid has also evolved a female mimic, one so good that he sometimes fools even fellow female mimics, who approach in search of copulation. This is yet another case of deception being too convincing for its own good.
DEATH AND NEAR-DEATH ACTS
It has long been known in predator/prey relations that deception can work anywhere from first detection until final consumption. Consider two examples near the time of death itself. The feigning of death typically occurs after the prey is caught, and is thought to inhibit the final death-dealing strike. The bird acts dead, lifeless, but remains conscious and alert so that often the only sign of life is its open eyes. Chickens run at the first opportunity, typically when the predator lets go, but a duck threatened by a fox often remains immobile for some time after release, especially if other foxes appear to be present. The fox’s counteradaptations are to kill some prey immediately upon capture and to disable the remaining ones by severing a wing on each.
In the broken-wing display, a bird near its nest tries to distract a potential predator by acting like an injured bird, with one broken and extended wing. The bird moves awkwardly near the predator with wing extended but flies away quickly when attacked. This display is much more dramatic the closer the predator is to
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