Olfactory Camouflage — The Squirrel Wore 'Eau de Snake'

Olfactory camouflage — applying a scent to mask a creature's own odor — is rare among vertebrates.

Scientists at the University of California, Davis recently published a paper documenting just that.

Here's Henry Fountain's "Observatory" column item from the February 5, 2008 New York Times Science section with the details.

Ground Squirrels Chew Snakeskins to Mask Their Scent

Here’s an odd animal behavior for you: the California ground squirrel chews on the molted skins of one of its main predators, the rattlesnake, and applies the scent to its body by licking itself all over.

This eau de snake has a purpose, says Barbara Clucas, a doctoral student at the University of California, Davis. It acts as camouflage, covering up the squirrel’s own scent so a meal-seeking rattlesnake will leave it alone.

Camouflage is nothing new in nature — it’s used by animals big and microscopic, and by plants, too. But among vertebrate animals at least, most of the deception is visual. The California ground squirrel’s behavior is a rare documented case of olfactory camouflage among vertebrates, Ms. Clucas said.

The squirrels are not the only rodents to chew snake skins, nor the only animals to apply the scent to their bodies. Ms. Clucas said that with the ground squirrels it seemed likely that the behavior was an antipredator one, because adult males, which are resistant to snake venom, don’t do it. Squirrel pups, which are not resistant, do the chewing, as do their mothers, which are resistant but look after the pups in the burrows.

Ms. Clucas and two colleagues, Donald H. Owings and Matthew P. Rowe, tested the reactions of hungry rattlesnakes to pieces of filter paper with rattlesnake scent alone, squirrel scent alone and a combination of the two. The snakes flicked their tongues over the squirrel-only scent, but not over the combined scent or the snake-only scent. The finding, reported in The Proceedings of the Royal Society B: Biological Sciences, suggests that if a rattlesnake is hovering over a squirrel burrow, it can be tricked into thinking that there are no squirrels there.

Ms. Clucas noted that people tend to think of camouflage more in visual terms. “But there are a lot of animal predators where the main sense they use is olfaction,” she said. “So this kind of behavior could be more widespread.”

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In the photo heading this post, a ground squirrel chews rattlesnake skin in preparation for scent application.

Want more on the subject?

Here's the abstract of the paper, as published online on January 15, 2008 in The Proceedings of the Royal Society B: Biological Sciences.

Donning your enemy's cloak: ground squirrels exploit rattlesnake scent to reduce predation risk

Ground squirrels (Spermophilus spp.) have evolved a battery of defences against the rattlesnakes (Crotalus spp.) that have preyed on them for millions of years. The distinctive behavioural reactions by these squirrels to rattlesnakes have recently been shown to include self-application of rattlesnake scent—squirrels apply scent by vigorously licking their fur after chewing on shed rattlesnake skins. Here, we present evidence that this behaviour is a novel antipredator defence founded on exploitation of a foreign scent. We tested three functional hypotheses for snake scent application—antipredator, conspecific deterrence and ectoparasite defence—by examining reactions to rattlesnake scent by rattlesnakes, ground squirrels and ectoparasites (fleas). Rattlesnakes were more attracted to ground squirrel scent than to ground squirrel scent mixed with rattlesnake scent or rattlesnake scent alone. However, ground squirrel behaviour and flea host choice were not affected by rattlesnake scent. Thus, ground squirrels can reduce the risk of rattlesnake predation by applying rattlesnake scent to their bodies, potentially as a form of olfactory camouflage. Opportunistic exploitation of heterospecific scents may be widespread; many species self-apply foreign odours, but few such cases have been demonstrated to serve in antipredator defence.