By Hunting Rodents, Raptors Help With Flood Control
Birds are good for more than controlling crop pests in Southern California’s Ventura County, where Barn Owls and other raptors protect an entirely different resource—56 flood-control dams and 40 miles of earthen levees—from burrow damage by ground squirrels and gophers. (See related article: At Orchards and Vineyards, Birds Are Outperforming Pesticices.)
A single gopher can excavate a ton of soil a year, and ground squirrels can burrow more than 30 feet. Networks of tunnels undermine levees.
“That’s actually happened,” says David Torfeh, the raptor program coordinator for Ventura County Watershed Protection Operations and Maintenance. “A sinkhole opened up when a truck was driving over it.”
The greater danger is a surge of runoff that will blow out a dam or levee, flooding property and even threatening lives. Ventura County had been using rodenticides to control squirrels and gophers for years, but managers were concerned that non-target animals—such as coyotes, bobcats, and mountain lions—might eat the bait or poisoned rodents. Several years ago they investigated a program in neighboring Santa Barbara County using raptor perches to attract hawks, owls, and falcons that control pests.
Soon after, Ventura County launched its own program, installing 14 T-shaped perches, each 20 feet high, along a mile of earthworks. As Torfeh says, they aimed to attract “any raptor that hunts for mammals.”
The perches worked, as Torfeh and his colleagues began seeing Cooper’s Hawks, White-tailed Kites, Red-tailed Hawks, Great Horned Owls, Northern Harriers—about a dozen species in all. They also installed nest boxes and a platform. Some 40% of the boxes attracted nesting Barn Owls.
In follow-up studies to compare the raptor-patrolled area to a nearby area baited with rodenticides, Torfeh and colleagues found that raptors were up to 67% more effective than rodenticides in controlling rodent burrows.
“The results were pretty amazing,” Torfeh says.
Now the county has installed more than 200 raptor perches and about 20 owl boxes on 30 miles of levees.
“Raptor perches save us about $7,500 a year compared to using anticoagulant [rodenticides] and a contractor who’s skilled at pesticides to monitor them,” Torfeh says. “We’re getting the word out to agriculture through the resource conservation districts of California about the program, because the more they use it the better it is for the environment.”