Ravens to threaten tortoises nevermore

 

The last person to see a raven feasting on baby tortoises in the California desert may be a federal agent, looking through the scope of a rifle. Ravens have been charged with contributing to the decline of the threatened desert tortoise, and the U.S. Fish and Wildlife Service is proposing to restore balance by shooting, poisoning and trapping the gregarious birds.

Ravens pluck off the legs and heads, or puncture the soft shells and pull out the innards of juvenile desert tortoises (no wonder the tortoise spends 95 percent of its life in burrows). Human settlement in the 25-million-acre California desert has favored ravens, which love trash, roadkill and crops, and hindered the lumbering tortoise, which now must compete with livestock for forage and evade human collectors.

Roadrunners and red-tailed hawks also snack on the squishy hatchlings. But studies document the extent of raven predation: over a four-year period, 250 juvenile tortoise shells were found under one nest. And since 1969, the raven population has increased 700 percent in some areas of the California desert, while desert tortoises have continued to decline. So, ravens are taking the heat.

“It’s a known problem and threat, so we’re focusing on it,” says Judy Hohman, a biologist with the Fish and Wildlife Service in Ventura. “But ultimately, if we want to help the tortoise, we have to deal with a lot of threats – not just this one.” To that end, the agency is also researching tortoise diseases and protecting nesting sites. Its preferred alternative for raven control includes limiting human-constructed nest sites (billboards, abandoned cars, communication towers) and human sources of food and water. Hohman and the Desert Managers Group, a consortium of county, state and military agencies in Southern California, also want local residents to close garbage cans and help clean up unauthorized dumps.

Such a holistic approach, which addresses human influence, is essential for raven reduction to be effective, says John Marzluff, a raven specialist. If ravens are simply killed without removing nest sites, water, and food, surviving birds just repopulate the area. Marzluff also contends that raven overpopulation indicates an ecosystem out of balance, with “sprawling urbanization and agriculture, winding roads and sloppy habits.” Before Westerners pull the trigger, he says, they should look at the larger picture.

The Fish and Wildlife Service began developing ideas for tackling the raven predation problem in 2004. Its Draft Environmental Assessment is available for public comment until May 7.
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