by MARY PAPENFUSS
June 10, 2019
Drones Mobilized To Battle Ravens Eating Baby Tortoises In California Desert. The machines are coating bird eggs with oil so they won’t hatch to feast on dwindling desert tortoise populations.
cientists are turning to technology to give desert tortoises
a fighting chance against the burgeoning and rapacious population of ravens in the Mojave Desert
The raven population in the western Mojave has increased more than 700% in the last 25 years and threatens to wipe out desert tortoises if nothing is done. In some places, “where there used to be 10 ravens, there are now 15,000,” Allison Fedrick, tortoise outreach and animal care keeper at The Living Desert, said.
In contrast, the number of desert tortoises in the western Mojave has plummeted by more than 90% since 1990. Although the turtles are also hit by cars, wiped out by development and energy operations and felled by disease, ravens were a critical factor. The birds are capable of pecking holes in the shells of tortoises up to 10 years old. One study found the carcasses of 250 juvenile tortoises
beneath a single Mojave raven nest over a four-year period.
Research biologist Mercy Vaughn and self-described “life-long tortoise biologist” Tim Shields are spearheading the drone project in coordination with the U.S. Fish and Wildlife Service. Over the past two months, their team has oiled 525 raven eggs in 116 nests on public land that is considered critical habitat for desert tortoises.
Surveys conducted in 1994 turned up 250 tortoises per square mile in some areas. Now, there’s maybe one or two. Four years ago, biologist Tim Shields began to experiment with egg oiling, a long-established, relatively humane method for reducing reproductive output of ground nesting birds such as Canada geese, which damage lawns, and double-crested cormorants, which compete with trawlers for fish.
The population of the common raven is exploding across the American West, where it thrives on human refuse and roadkill. As the large, strutting predators piggyback on the spread of human civilization, they are expanding into territories where they have never been seen in such large numbers.