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Unmanned cameras reveal social life of gopher tortoise

 
Published Dec. 14, 1998|Updated Sept. 14, 2005

For years scientists figured that the gopher tortoise must be a solitary animal. It lives in a burrow. It emerges for a little while in the morning and evening to forage for food. Otherwise it stays underground, out of the sun and out of sight.

How sociable could it be?

Very, it turns out. In fact, the tortoise is quite the social butterfly, scientists at the Tall Timbers Research Station near Tallahassee have learned.

"The animals interact with each other a lot more than most of us thought," research scientist Sharon Hermann said last week.

To preserve the vanishing gopher tortoises, biologists need to know more about how they behave. When Tall Timbers scientists set up unmanned cameras at the entrance to tortoise burrows, they caught the gophers engaging in everything from combat to courtship _ although sometimes it was difficult to tell which was which.

"We have one roll of frames showing interaction between a male and a female that literally goes on for 20 minutes," Hermann said.

Piecing together the sometimes blurry pictures as if assembling a children's flip book, the scientists saw the two gophers circle each other warily. Then one ventured into the burrow while the other sidled out. Then they were both outside.

Gophers fight by trying to tip each other over, like slow-motion sumo wrestling. These two were clearly jockeying for position. Were they getting ready to rumble or dancing a mating minuet?

The answer turned out to be the latter.

"On the last frame of the role," Hermann said, "we could see the start of mating behavior."

Although other researchers had previously found anecdotal evidence of the gophers' social behavior, the pictures shot by Tall Timbers and another such project at Auburn University paint a far more detailed portrait of what their lives are like.

Both projects are helping biologists figure out how tortoises get along with each other at a time when there are considerably fewer gophers than there used to be. Development and disease have been blamed for their decline.

Gopher tortoises once were so common throughout the Southeast that during the Depression, the poor dubbed them "Hoover chickens" and ate them.

First described by naturalist William Bartram in 1791, the gopher tortoise digs burrows as much as 40 feet long and 18 feet deep. In the burrows the tortoise can keep cool during the heat of the day, dodge predators and avoid the occasional wildfire.

"They don't tend to own their burrows, but each animal uses two to four burrows, all in the same neighborhood," Hermann said.

The gophers' many burrows can provide shelter for 360 other species of animals, too, including rabbits, quail, armadillos, indigo snakes and opossums. The loss of gopher tortoises, and their burrows, would upset the balance of nature.

But the scrub sand hills, oak hammocks and wire grass flat woods where the gophers thrive are ideal for subdivisions. Mining for phosphate, rock and sand destroys gopher habitat as well.

Meanwhile, a deadly respiratory disease that appeared among gophers in Lee County in the 1980s has rippled through the species. The disease spread probably through the gophers' method of greeting, which is rubbing noses, said George Heinrich, a biologist at Boyd Hill Nature Park in St. Petersburg and co-chairman of the Gopher Tortoise Council.

So far there is no cure and no money for finding one, Heinrich said.

In Florida, the gopher is now classified as a species of special concern, and in some other states it is considered endangered. One study predicted gophers won't exist outside nature preserves by 2000.

In recent years, when an area that gophers call home has been slated for destruction, state or local government officials required the developer to relocate the tortoises. But moving the tortoises does little for the other animals using their burrows, Heinrich said, and could spread the gophers' disease into areas where it did not previously exist.

Scientists need to know more about the tortoise to save it. "This guy, because he lives in a burrow, has escaped a lot of attention," Hermann said.

The gopher prefers it that way. There is some evidence the gophers can pick up the vibrations of approaching footsteps, so they can hide in their burrows when people come around.

"They know you're coming before you know they're there," Hermann said.

As a result, said Auburn University professor Craig Guyer, "You can find their burrows very easily, but finding the animals is very difficult."

Guyer and his students have been using unmanned cameras to study gopher tortoises in Florida, Georgia and Alabama for three years.

The Auburn cameras caught gophers leaving their burrows for no more than half an hour at a time. It was long enough for the tortoises to make every appointment on their social calendar: Browse the buffet, greet the neighbors and, after everything else was done, find a mate.

"The biggest surprise, the thing nobody had ever described before, was that the mating happened at the very end of the day," Guyer said.

The researchers had some disappointments. The shutter of the camera is operated by a pressure-sensitive switch at the entrance to the burrows. The pressure needed to click the shutter was so slight that "we took more pictures of rain than anything else," Guyer said.

In some cases, the pictures they did get produced more questions than answers. For instance, Hermann said, although the Tall Timbers cameras caught male tortoises fighting, it did not show why.

"It may be competition for mates," she said, although there is also some suggestion that the females choose which males will be their mates, not the other way around.

Perhaps the finding with the most far-reaching consequences has come out of the Auburn study. There, Guyer and his students put 15 of their cameras in areas where the tortoise habitat was in good shape and 15 where it was not.

In forests undisturbed by man, Guyer and his students found that gophers "stay at the same burrow for a long period of time. They know each other as neighbors and socialize on a daily basis."

But in disturbed areas, Guyer said, the tortoises' social behavior was disrupted. They did not stay in the same area long, changing burrows frequently.

"We can't document that it's bad, but we want to collect more information," he said. For a socializing gopher, keeping the old neighborhood intact "is likely to be as important to him as it is to humans."