A SPECIAL GROWERS’ REPORT OF AG ALERT ® CALIFORNIA Trees & Vines
®
Owl study assesses rat management in nut orchards By Vicky Boyd For more than a decade, university wildlife researchers have studied how installing Funded by a $923,954 grant from the California Department of Pesticide Management, Johnson and fellow researchers will focus on roof rats in almond and pistachio orchards. Nestlings spend about two months in the owl box before they’re ready to try their wings. As many as a half dozen owlets typically fill a box, and they eat up to four to five rodents daily. Below, some nut producers, such as this Stanislaus County pistachio farm, have erected barn owl boxes for rodent management.
Joining him is University of California Cooperative Extension wildlife management specialist Roger Baldwin, who conducted research previously into managing roof rats in citrus orchards. In that project, Baldwin said his research team found that citrus trees’ dense canopies and ever- green foliage hindered barn owl’s foraging on rats. But the researchers had good success using elevat- ed bait stations with a small amount of toxicant to knock down rat populations. Then they followed up with trapping to maintain the low numbers.
barn owl nesting boxes and accompanying owl pre- dation help manage small rodents in vineyards. Now they hope to take a similar approach during a three-year study that examines the effects of barn owl predation alone or combined with trapping to potentially manage roof rats in nut orchards. “We’ve documented that barn owls do indeed reduce the number of voles, gophers and mice, and we’ve learned a lot in the vineyard systems,” said Matthew Johnson, a Cal Poly, Humboldt, wildlife professor who led much of the research. “Now we’re really excited to try some similar approach- es in orchards.”
While nut orchards also provide an arboreal environment, Baldwin said they’re deciduous and drop leaves seasonally, unlike citrus. He the- orized this may push rat activity onto the orchard floor in the fall, making them more vulnerable to owl predation. See OWLS, Page 8
Although many growers have erected owl boxes to control small rodents in vineyards, he said little scientific data existed until recently about barn owl predation and how cultural practices influenced it. There’s been even less research into the feathered predator’s impacts on orchard rodents.
6 Ag Alert September 16, 2026
Powered by FlippingBook