Ravens May Be Killed to Save Desert Tortoises

State and federal wildlife officials are drafting a proposal calling for selective shooting and poisoning of ravens in the Mojave Desert that are killing large numbers of the threatened desert tortoise.

The proposal is being written in the California field offices of the U.S. Fish and Wildlife Service and the Bureau of Land Management, which says the population of young tortoises is being decimated by the ravens in western regions of the desert near Barstow.

The plan, is expected to be made public in December, and could go into effect next spring, after being reviewed by animal welfare groups and the public. Federal officials said the plan is supported by the California Department of Fish and Game.

“We’ve decided on a pilot program,” said BLM biologist Kristin Berry. “It will involve some shooting of known or suspected killer birds and some poisoning.” The number of ravens taken under the initial program would be in the “low hundreds,” she said, though that would go up if the effort is expanded later.

Endangered Species

The Fish and Wildlife Service recommended the desert tortoise for protection as an endangered species three years ago in the wake of studies showing that the size of the habitat and the population are declining seriously.

While the raven population was once thought to be declining as well, recent figures from the federal Breeding Bird Survey show the numbers in Southern California have grown 328% over the last 20 years, apparently due to dumps and other feeding areas created by increasing urbanization.

Experts say young tortoises are proving a popular meal for at least some ravens. Before tortoises reach the age of 7 years, experts say, their shells are as soft as human fingernails and can be penetrated by the ravens’ powerful beaks.

In the western Mojave Desert, research shows that the tortoise population has declined from 30% to 70% in the last six years. As many as 88% of the young tortoises, the sort preyed upon most by ravens, have been killed in some areas, Berry said. One pair of breeding ravens alone is believed to be responsible for the killing of more than 250 juvenile tortoises, she said.

Because of the killings, “you do not have the normal population” of juvenile tortoises in the Mojave, including sites near Needles and Mojave, and in some sections there are none, said Berry. While thousands of tortoises still remain in the desert, Berry said, certain age groups are disappearing. The killing of tortoises is occurring both inside and outside the preserve known as the Desert Tortoise Natural Area.

Those drafting the proposal believe that if the killing of young tortoises is a learned behavior it could be controlled by eliminating the birds doing most of the killing. Ravens, members of the crow family, are among the most intelligent birds and have demonstrated an ability to learn comparable to mammals, a fact that could stir the opposition of some animal lovers.

The poison under consideration is a starlicide, so called because of its past use on starlings, and is considered fairly specific for crows and ravens. Don Moore, a Ridgecrest representative of the National Audubon Society who recently attended a meeting on the raven control proposal, said one possible use of the poison would involve injecting it into chicken eggs, which would then be placed as bait for the birds.

Moore agreed that the situation for the tortoises in some parts of the desert is “approaching desperate.” But Dan Taylor, Western regional representative of the Audubon Society in Sacramento, said “our initial reaction” to the proposal “is one of great caution. We don’t like it until proven otherwise.”

Other Threats

Ravens are only one cause of difficulties for the desert tortoise, Moore said. He named off-road vehicles and shooting by vandals as other causes, and worried that ravens may bear the brunt of enforcement. According to Moore, of 489 tortoise shells analyzed over the last five years, 30% of the deaths were linked to ravens, 19% to vandalism, and 2% to off-road vehicles.

“The BLM may tout this as evidence to do something to help the tortoise when it may not do as much” as they think, Moore said. For one thing, if the killing of tortoises is widespread among the ravens, killing a selected number might not have any effect.

Berry said, however, that selected killing had previously been used to keep ravens away from nests of the California least tern. Though the numbers were much smaller than contemplated here, she said, there was quite an increase in nesting success.

The pilot program, she said, would last several months in the spring and summer of next year. After that, the project team would determine whether it should be expanded.