cover story


Wildlife biologist Sofi Hindmarch with barn owl.


Natural allies threatened


Raptors help keep farmrodent populations in check—if the birds can survive poisons that also are used to deal with the problem.


By Judie Steeves N


aturally, the best method of control for outdoor rodent pests is encouraging raptors such as owls and hawks to patrol your fields for you. Ironically, people are killing these natural controllers of rodent populations by careless use of poisons intended to kill rodents.


When raptors hunt rodents and happen to consume those that have ingested poisons such as warfarin, those poisons can also affect the big birds. (Warfarin-containing baits are not approved for field use.)


While they might not die immediately or directly, the poisons get into their internal organs, accumulate, and can affect their ability to navigate and avoid such dangers as moving vehicles and power lines, so they die—sometimes as an indirect result of the poison they ingested. With this in mind, it’s essential if you use pesticides to combat problems with voles or field mice that you use the correct product and in the right way.


For instance, only Ramik brown, Ramik green and Ground Force paraffinized pellets are approved for field use. Hombre, Weatherblok XT, Ratak and Terminator are not.


6 British Columbia Berry Grower • Summer 2016


All approved anticoagulant rodenticides must be placed in bait stations in the field, to prevent access by children, pets, livestock and non-targeted wildlife. Irene Wilkin, regional pesticides officer with the Pesticide Management Regulatory Agency, explains that growers must read the label before using any pesticides, even if it’s one that has been used many times before, because there have been changes in regulations in recent years as more has been learned about the impacts of their use.


If you’re purchasing rodenticides, ask for those approved specifically for field use. Those rodenticides labelled for indoor use or in and around buildings are prohibited for use in agricultural fields, and must always be placed in sturdy locked bait stations.


Around packing plants, Wilkin advises, baits should be placed by a professional pest control specialist. Above all, rodenticides should not be the first line of defence. Instead, encourage raptors, which are natural enemies of rodents, to patrol your fields, and only use pesticides as a last resort.


Sofi Hindmarch is a Fraser Valley wildlife biologist who specializes in raptors and says since the 1990s, hundreds of raptor carcasses tested have had high concentrations of rodenticides in their systems.


The health of barn owls are of particular concern because voles are a favoured part of their diet, but the lives of kestrels and falcons are also of concern, she adds. Barn owls are currently being upgraded to threatened status in Western Canada.


In a study conducted in Delta recently, Hindmarch learned that a large percentage of farmers use


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