Contrasting Serpent Problems Challenge CU-Boulder Professor

March 10, 1997

Two island-dwelling snake species under study by a University of Colorado at Boulder expert present contrasting challenges to researchers attempting to rectify growing ecological problems associated with the reptiles.

One, the Aruba Island rattlesnake, is now so rare on the island north of Venezuela that there are roughly as many in captivity -- about 200 to 300 -- as there are in the wild, said psychology department Professor David Chiszar. Dwindling habitat on the tiny island is the primary force driving the venomous snake toward extinction, said Chiszar, a nationally recognized herpetologist and animal behaviorist.

Ideally, captive-born Aruba Island rattlers could be used to repopulate portions of the rapidly developing island that are suitable for reintroduction. “But these snakes show little or no fear of predators and generally don’t rattle, which is exactly the kind of behavior that will get them killed in the wild,” he said.

In a project designed to mitigate what he calls “behavioral deficits” in captive-born Aruba rattlers, Chiszar has built an artificial habitat with rock piles, trees and cacti similar to the snake’s natural habitat. Unlike wild rattlers -- which head for the enclosure’s rock piles and disappear in seconds -- the Aruba snakes may take up to two weeks leisurely exploring the room before heading for rocky hideouts, he said.

Once they begin using cover, however, “A light bulb goes on and the snakes start exhibiting defensive behaviors,” he said. “While these behaviors are innate, they must first be elicited and then maintained in order to facilitate survival.”

Chiszar also is beginning a study to see if lab-raised Aruba rattlers have the ability to locate places with suitable temperature and humidity conditions for survival in the wild. He first will test wild rattlers in the lab, then compare their behavior with that of captive-born Aruba rattlers. When a snake sheds its skin, for example, it often requires a place with specific humidity conditions, he said.

A final decision on any reintroduction efforts will be made by the Aruban government, said Chiszar, who has traveled to Aruba twice for snake conferences and is collaborating on the project with R. Andrew Odum of the Toledo (Ohio) Zoo.

The brown tree snake, also under study by Chiszar, is more familiar to the public. Native to Indonesia, the Solomon Islands, New Guinea and Australia, the snakes are believed to have been introduced on Guam as airplane or ship stowaways in the late 1940s or early 1950s. Since then, they have wiped out native wildlife populations and wreaked havoc with Guam’s electrical power systems.

In addition to extirpating 12 bird species and endangering several other bird, bat and lizard species on Guam, the snakes often crawl onto power lines. They have triggered more than 1,200 power outages on the island, causing millions of dollars in damage to electrical and computer systems and refrigerated goods, he said.

Chiszar, who has studied the climbing behavior of brown tree snakes and helped design snake barriers for use on Guam’s power poles, is now searching for the most effective chemical cues that can be used to lure the snakes into traps.

Although the best bait for snake traps is live rodents, Chiszar believes he is on course to develop a chemical attractant that could be up to 80 percent as effective as live animals. The snakes, which can reach more than eight feet in length, are found in densities as high as 13,000 individuals per square mile in certain areas of the island, although 2,000 to 3,000 snakes per square mile is closer to the average.

Chiszar, who specializes in the sensory systems that control predatory behavior in reptiles, said the long-term goal of the project is to eradicate the brown tree snakes on Guam. In the meantime, control programs may allow biologists to provide “sanctuary-type areas where endangered birds, bats and lizards can breed.”

Chiszar, who is collaborating with Tom Fritts of the U.S. Fish and Wildlife Service and others on the effort, said there is concern the snakes may eventually make their way to Hawaii and impact native wildlife there.

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