by Whit Gibbons

July 5, 2015

Fighting back, running away and hiding are three instinctive responses if a person feels threatened. Many animal species do likewise, and some have their strategies honed to perfection.

An admirable combination of escaping death or injury by leaving the danger zone followed by concealment is practiced by Cope';s gray treefrog, a species found throughout most of the eastern United States. Many people have heard the musical trills of these little vocalists as they call from trees on summer nights. But in daylight you could walk right past one sitting on the trunk of an oak tree. If the frog doesn't move, chances are you will not see it because of its amazing camouflage. It looks like gray bark.

Many birds have no qualms about eating small frogs, so how does this seemingly defenseless creature escape if it is moving around and gets spotted by a hungry bird? Step one for the frog is a big one. It jumps toward another tree. While in the air, it spreads out its hindlegs, revealing a bright yellow blotch on the back of each thigh. The bird meanwhile is making its move, presumably focused on the fast-moving yellow target. But when the gray treefrog lands on a gray-barked tree and pulls its feet up alongside its body, to the eye of the bird, the yellow morsel of food has disappeared. The gray treefrog sits still, relying on its remarkable camouflage against the tree. The hapless bird is still looking for something bright yellow.

The phenomenon is known as flash coloration, wherein a prey animal exposes an obvious and colorful part of its body and then conceals it, allowing the animal to blend in with its background. If the acrobatics, misdirection and camouflage do not work for a Cope's gray treefrog, it has one last trick up its sleeve. In a sense these treefrogs fight back: They are poisonous to touch. They don't bite, but the secretions on their skin are extremely noxious and can be transferred from the frog to the eyes, mouth or lining of the nose of someone who picks one up. It once took me two painful hours before I could open my eyes and see again after capturing a gray treefrog in a swamp. After handling it I foolishly rubbed my eyes. A predator catching a gray treefrog would have a not-so-tasty meal to deal with.

Screaming is another common way humans deal with a menacing adversary. And so do some animals. I recently heard a rabbit scream when I went out to get the newspaper before daylight. This troubling sound is reminiscent of a wailing child and will definitely give one pause when standing in the driveway in the dark. I can only imagine the chill bumps had I been deep in the woods. Some frogs are known to give a loud, similar-sounding distress call when being attacked by a predator, often a snake. Screaming by a bullfrog can be evoked on rare occasions by a person catching one. I have observed this behavior once and assure you that an open-mouthed, shrieking bullfrog is disquieting.

One explanation for this behavior is the predator attraction hypothesis. The sequence has been confirmed in one case I know of. A snake grabbed a frog as prey; the frog screamed; a hawk heard the scream and headed for the scene of the crime. The hawk captured the snake, which was occupied with the frog and also was a bigger meal. Meanwhile, the snake released the frog and turned its attention to its attacker. Of course, the hawk might have eaten the frog, but its odds of escaping had definitely increased.

Similarly, a bobcat or coyote hearing a screaming rabbit in the woods might head toward the sound with expectation of some kind of meal and inadvertently disrupt the attack against the rabbit. I, meanwhile, would be headed in the other direction at the sound of a shrieking rabbit.

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