Owl that talks with a forked tongue

Press, 26 July 1986, Page 21

Owl that talks with a forked tongue

Camouflage we are familiar with, but a bird that pretends it’s a snake? STEPHEN YOUNG of the London ‘Guardian” plumbs the depths of natural ingenuity.

Scientists from California have been studying an owl that masquerades as a venomous snake. The owl is not the victim of a split personality, neither is it an avian Walter Mitty; its aim is simply to confuse Its enemies. The research comes from Matthew Rowe, Richard Coss, and Donald Owings, who are ecologists from the University of California at Davis. The object of their attentions was the burrowing owl Athene cunicularia, which is in the habit of sheltering and nesting in tunnels made by rodents. When disturbed it gives out a local hiss or buzz that sounds just like an angry rattlesnake — a species that also happens to lie up in burrows. The resemblance between the two sounds was noticed as long ago as 1882. But is anyone actually fooled by a cornered owl? The Californians were the first to put the theory to the test .

The owl’s hiss could be aimed at the owners of the burrows — such as ground squirrels — who are competitors for living space, or at predators such as American badgers, skunks, or coyotes. Either way the bird has a good

deal to gain by creating a menacing public image. In the event, the scientists chose to do their experiment on ground squirrels, since the powers of discrimination of these rodents are known to be rather sophisticated. For example, they can estimate the size of a rattler from the sound of its rattle. If the owl can pull the wool over the squirrel’s eyes, or rather its ears, then it can fool other creatures as well.

Tests were designed to reflect natural encounters as far as possible. Squirrels that were about to enter a burrow-like

chamber were played tape recordings of a large rattler, a burrowing owl’s hiss, a burst of white noise, or a second sound from the owl, described as a scream-chatter. The team carefully monitored the squirrel’s reactions to the sounds, looking at its position in the artificial burrow and taking various measures of its state of excitement.

The experiment vindicated 100 years of theory. Squirrels found the owl’s hiss almost as alarming as the authentic rattle, but were not unduly worried by the scream-chatter. They could dis-

Since squirrels are clever judges, the biologists conclude that the theory is not only appealing, but true. The owl really does mimic a cornered rattlesnake with sufficient skill to fool its competitors, and probably its predators too. The research highlights the possibilities of acoustic deception — an approach that may pay dividends to other species of bird. For example, the crested guan, a Central and South American relative of the domestic

tinguish the sound of a rattler from white noise, but not from the owl’s best efforts.

chicken, has a sound in its repertoire that is said to resemble a jaguar’s growl. Even the humble great tit hisses when its nest is approached. The sound may be designed to resemble the voice of a snake, or even a tetchy weasel. These ploys have much in common with more familiar forms of mimicry, such as that practised by hoverflies. These insects put on the protection of a black and yellow livery and reap the benefits of looking like wasps. People who fix the gutless metal boxes of burglar alarms to their window sills are using the same ruse. However, these asses in lions' skins have no monopoly on deceit. A benign image can be as useful to the hunter as a malign one is to the hunted. The devil’s flower mantis, for example, waylays its victims by imitating the flowers on which they feed, while the sabre-toothed blenny goes forth in the colours of the helpful cleaner wrasse, thus gaining a mantle of innocence in which to attack its victims.

The burrowing owl has merely extended the art of deception to the acoustic realm.