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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