The federal government is expected to issue a permit that will allow the shooting and poisoning of up to 1,500 ravens that are believed to be killing large numbers of already imperiled tortoises in the Mojave Desert.
Dave McMullen, assistant regional director of the U.S. Fish and Wildlife Service in Portland, Ore., said the permit will likely be issued within a week. “They can start right after that,” he said.
Final interagency agreements between the California Department of Fish and Game, the Fish and Wildlife Service, and the federal Bureau of Land Management must be signed before the start of the program, but officials want to begin as soon as possible.
This is a critical time, according to biologists, because early spring is a key feeding time for juvenile desert tortoises. It is when they are young and their shells are as soft as human fingernails that the tortoises are most vulnerable to the strong, sharp beaks of ravens.
McMullen said one condition that might be attached to the permit would require poisoning to be stopped if other birds or animals take the bait and begin dying. It is expected that the actual shooting and poisoning will be done by animal damage control experts from the U.S. Department of Agriculture.
The permit application was filed several months ago in the aftermath of studies showing the tortoise population and habitat area has declined dramatically in recent years.
While the raven population had been thought to be in decline as well, recent figures from the federal Breeding Bird Survey show their numbers in Southern California have grown 328% over the last two decades, apparently due to dumps and other feeding areas created by growing urbanization in the desert.
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 preferred by ravens, have been killed in some areas, according to BLM biologist Kristin Berry. One pair of breeding ravens alone has been 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, Berry said recently. The control program is expected to focus on three areas, one in the western Mojave near the Desert Tortoise Natural Area, at sites near the Twentynine Palms Marine Corps Air Ground Combat Center, and over a 250-square-mile zone near Needles, McMullen said.
BLM wildlife experts said that if the killing of tortoises is a learned behavior it could be controlled by eliminating the birds doing most of the killing. The raven, a member of the crow family, which is protected by the Migratory Bird Treaty Act, is among the most intelligent of birds and has demonstrated an ability to learn comparable to mammals, a fact that has made some animal lovers reluctant to support the raven killing program.
McMullen said the program will not threaten the larger bird population. He said the total population is thought to number around 10,000.
One poison under consideration is a starlicide, so called because of its use on starlings. It is considered fairly specific for crows and ravens. Don Moore, a Ridgecrest representative of the National Audubon Society familiar with the raven control proposal, said one possible way to administer the poison is to inject it into chicken eggs, which would then be placed as bait.
Moore has agreed that the situation for the tortoises in some parts of the desert is “approaching desperate.”
But the Audubon Society’s senior vice president for science and sanctuaries, J. P. Myers, said there is no clear showing that the ravens are at the heart of the tortoise decline and consequently the society could not support the proposal because it is not certain that killing ravens will have the desired effect.
Berry said, however, that selected killing had previously been used to keep ravens away from nests of the California least tern.
Ravens are only one cause of difficulty for the desert tortoise, Moore has said. He named off-road vehicles and shooting by vandals as other causes of tortoise deaths, and worried that ravens might bear the brunt of the enforcement effort.