Winemakers in California are studying a novel way to reduce the toll rodenticides take on birds of prey – using the birds themselves to control mice and rat plagues.
Instead of laying down poisons, vineyard owners are encouraging an enemy of rodents, the barn owl, to establish territories among the vines. In turn, it is hoped the hungry owls will eat into the rodent problem.
The study is of interest to Tasmania where the growing use of ever-powerful rodenticides is having an impact on raptor populations, and other species like tawny frogmouths which at times hunt mice.
And it comes at a time when Australian birdwatchers have been targeting hardware chains in a campaign to get them to stop selling the more lethal poisons.
In the Napa Valley in California – an area world famous for its wines – many winemakers have been taking part in an experiment to determine a more natural approach to controlling rodents.
The experiment is part of a long-term study by researchers at California’s Humboldt State University in which around 300 owl nest boxes have been placed throughout vineyards. These are being used to document if owls are more successful at removing pests than rodenticides.
The researchers have surveyed 75 wineries in the Napa Valley, and four-fifths now use the owl nest boxes and notice a difference in rodent control. The barn owls have a four-month nesting season, during which they spend about one-third of their time hunting in the fields. A family of barn owls may eat as many as 1000 rodents during the nesting season or around 3400 in a single year.
Although the research is ongoing and results have not been fully assessed, the researchers are optimistic it will prove an important tool in rodent control.
The barn owl is a universal species with a sub-species resident in Australia, although rare in Tasmania. More common here is a close relative, the masked owl, which would make an ideal candidate if the owl experiment was tried here.
Earlier this year, wildlife biologist Nick Mooney organised a series of workshops in which he outlined the threat modern rodenticides posed to birds.
The early anticoagulant poisons, called First Generation Anticoagulant Rodenticides (FGARs), required rodents to consume multiple doses, lessening the exposure of wildlife to the poisons. The new Second Generation Anticoagulant Rodenticides (SGARs) – used more widely because of the convenience of their “single-dose” effect – killed rodents more quickly but more residual poison was ingested by raptors or other predators.
Mooney said that when buying rodenticides it was important to look at the labels on the packaging which revealed active ingredients. It was also important to look for the words “single-dose action” which gave a clue to toxicity.
Less toxic (FGAR) poisons contained active ingredients called Warfarin and Coumateraly and the more toxic SGARs, Brodifacoum and Bromadiolone.