How the Gator Lures Lunch

PHOTO: Crocodiles and alligators have been found to balance sticks on their snouts as a way to lure nest-building birds into reach of their jaws.

Not too many years ago we were all taught that only humans used tools. Now, of course, we know that was rubbish.

Scientists have documented the use of tools by all sorts of animals, ranging from chimps to birds and even one species of fish. But it turns out that's not all of the story. One animal has been found to use tools not just as tools, but as lures to attract his prey into his happy hunting grounds.

And surprisingly, that animal turns out to be crocodiles and their close cousins, alligators, known collectively as crocodilians.

The tools?

Common twigs floating in swamps beneath trees that provide nesting areas for birds, including herons and egrets.

Here's how it works, according to Vladimir Dinets, an animal behaviorist in the department of psychology at the University of Tennessee, Knoxville, who has studied the feeding habits of crocodilians in both India and the United States.

Twigs are essential for birds to build their nests, and they are so scarce in some swamps that the birds fight furiously among themselves over just a few sticks. The birds build their nests in the tops of trees that grow in the middle of lakes because that protects their young from snakes and other animals that prey on the chicks.

So they have a symbiotic relationship with the crocs. The swamps provide a safe harbor for their nestlings, but if one falls into the lake, it's a small but easy snack for the big, powerful reptiles below.

According to Dinets, who has seen this many times, the crocks swim slowly beneath the twigs and then surface, carefully keeping the twigs on their snouts.

"It takes a balancing act to keep them there," Dinets said in a telephone interview.

The croc then remains motionless, just beneath the surface, waiting for a bird to try to grab one of the twigs. When the bird gets close enough, the croc uses its powerful tail to fling itself out of the water and snatch the bird.

"It all happens in less than a second," Dinets said. "It's a big splash, a snap, and a lot of feathers."

The first time he saw it, he said, he thought it was accidental -- maybe he just happened to be there when a bird tried to get a twig that had floated onto the nose of a crocodilian. But it happened too often to be an accident.

Dinets and his colleagues, J. C. and J. D. Brueggen, who run the St. Augustine Alligator Farm Zoological Park in St. Augustine, Fla., set out to document the activity at four sites in Louisiana, resulting in a study published in the peer reviewed journal Ethology, Ecology and Evolution. Two of the sites were breeding grounds for birds, and two were not.

The scientists saw a huge increase in the number of alligators with sticks on their snouts at the rookery sites where birds were building their nests, from March to May.

The researchers saw the drama unfold many times every day, but almost exclusively during the time that the birds were building nests. It rarely happened after the nesting season was over, leading the scientists to conclude that the sticks were indeed being used by the reptiles to lure the birds to their deaths.

"The present paper is the first report of tool use by any reptiles, and also the first known case of predators timing the use of lures to a seasonal behavior of the prey," the study concludes.

The scientists think they have produced evidence that crocodilians are just a lot cleverer than anyone had though.

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