Wildlife biologist Tim Pitz holds an adult golden eagle that was captured as part of a telemetry study. The study outfitted raptors with backpack transmitters to track their hunting, movement, and migration.
PHOTO B OURTESY OF NORTHWEST WILDLIFE CONSULTANTS
Efforts in the last few years to bring raptors into Oregon tree fruit orchards are paying off. Growers using perches and nesting boxes are reporting better control of their rodent populations, fewer damaged trees, and less need to use other tactics, like trapping.
Gabe Dahle of Dahle Orchards, who grows cherries with his father, Tim, in The Dalles, Oregon, said that years ago, they were losing so many young cherry trees to gophers that they began a very strict scouting and control program. “We’d scout for gophers several times a year, and if we found any evidence of activity, we’d go in the area in full force, using bait, the Rodenator blasting device, and other means. We were spending at least $50 an acre on rodent control.”
But since putting up about 50 barn owl and kestrel nesting boxes, they’ve seen a marked decline in their rodent populations.
Cherry grower Steve Sugg shares a similar story. His orchard, located south of The Dalles and surrounded by wheat fields, had a migrant gopher and vole population coming into the orchard from the neighboring wheat fields.
“When I planted, I didn’t take into consideration that I’d have so many gophers coming across the fence into the orchard,” he said. “At first, I couldn’t stay on top of the gopher damage.”
Sugg installed about 40 owl and kestrel nesting boxes across 300 acres during the last three years and says his gopher population is way down. His rodent control program involves encouraging raptor predators, and he uses the Verminator, a burrow building machine manufactured by the Inventive Products in Mountain Home, Idaho. “I hardly do any hand baiting or trapping anymore.”
With five barn owl boxes installed in her cherry orchard, Deb Morgan says she knows barn owls are working because she sees hundreds of owl pellets underneath boxes and along a 20-foot-high dirt bank where they also nest. “I’ve definitely seen a difference in our vole and mouse population in the orchard since putting up barn owl boxes.”
To encourage raptors to patrol his wheat fields, David Brewer has planted tall trees for raptors to perch in. “In open wheat fields, the limiting factor is a place to perch,” he said, adding that he’s also installed barn owl boxes in a barn.
The growers, who took part in a panel discussion at a raptor workshop, agreed that patience and perseverance are needed when putting up owl boxes.
“It’s really easy to get frustrated when you put up 50 boxes and you see only 5 to 10 occupied,” said Dahle. “Our first year, we had three owls occupy boxes that were made totally all wrong, and none occupy the perfectly made boxes.” He views 5 to 10 percent occupancy as a success. “Even if only 5 are filled, that’s five families getting 3,000 gophers each.”
Dahle sees 15 to 20 percent occupancy in other bird boxes (kestrels, bluebirds, other insect-eating birds). The highest occupancy he’s ever observed in his bird boxes is 30 to 40 percent.
He’s also found that kestrel boxes are attractive to pygmy owls, a species extremely aggressive in attacking starlings.
Mike Omeg, a grower in The Dalles, said that in his first year of putting raptors to work, only two of 50 boxes were occupied. But the next year he had 20 boxes serving as owl homes. Now, he has 75 boxes, and almost 50 are filled with barn owls. Not all boxes have clutches; some are used by single adults as bachelor or bachelorette pads. But, he points out, even single birds hunt rodents.
Growers must be patient when first setting up owl and kestrel boxes, says wildlife biologist Tim Pitz, who was also part of the raptor workshop in The Dalles. “It takes time and experimentation,” Pitz said, noting that humans can’t always create everything that the birds want.
As humankind has changed the landscape, planting a monoculture of vineyards and orchards, or other crops, what’s now lacking for many birds of prey is a home, he said. “If you can put a home for them in the middle of your orchard, then they now have a home and a food source.”
While the three tree fruit growers are noticing a difference in their gopher and vole populations, they are still having problems with ground squirrels, commonly referred to as “gray diggers.” Barn owls don’t control squirrels because the owls are nocturnal hunters and squirrels are only out of their burrows during the day.
Ground squirrels have been a particular problem at Dahle Orchards. “We’ve lost whole blocks of fruit on young trees to squirrels, where they come in and eat every single cherry,” said Dahle. He and his father now use a lot of corrugated tubing for bait stations that they set up in hot spots. The stations are filled with bait about twice a year. “And my dad does a lot of shooting,” he said.
Most growers in the area—even cattle ranchers—leave coyotes alone to encourage them to prey on squirrels and smaller rodents.
Red-tailed, rough-legged, and ferruginous hawks all hunt squirrels, according to Pitz of Northwest Wildlife Consultants. The red-tailed hawk, one of the most common hawks in North America, is found in all types of terrain, but needs perching places to be effective.
“They’re perch-and-drop hunters,” Pitz said of the large hawks. “The big-bodied hawks can’t fly for long periods of time because they expend too much energy when flying. They like to sit for long periods of time, and perches help them do that.”
Perches placed up above the tree canopy can give raptors an overview of the orchard and encourage them to hunt there.
“You want to get any type of raptor into your orchard that you can,” said Pitz, adding that there’s no such thing as a bad raptor on a farm.
Even great horned owls are good hunters. And though they have a reputation for taking out domestic cats, he believes that most cats are formidable hunters and the likelihood of losing a pet cat is small.