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cover story


Feathered allies in rodent fight


Barn owl nest boxes are being erected atop posts in poison-free berry fields around the LowerMainland. By Judie Steeves


T


he best control of small mammal pests such as voles is a natural one such as barn owls, and there’s a project underway that can help berry growers increase such controls and reduce damage from the little rodents. Sofi Hindmarch is a wildlife biologist who specializes in raptors in the Fraser Valley and says the big birds naturally help with vole control in berry fields, but they can use a little support, as their habitat decreases and threats to their lives increase.


She is coordinating construction of barn owl boxes to be erected atop six metre high posts in berry fields around the Lower Mainland.


In their night patrols of fields, owls become a farmer’s best friend, eating more rodents than most other predators and making them a most valuable ally of agriculture. In order to prevent death of the raptors, she will only erect the boxes in organic operations where the farmers can’t use rodenticides to combat such pests as voles. When raptors consume pests with rodenticides in their systems, those poisons accumulate in their bodies, often leading eventually to their death.


Last year, 16 of the owl boxes were put up, and if that experiment was successful, she’s hoping to expand the program this year, with the support of funding from the Investment Agriculture Foundation.


Voles are a main prey of the barn owl, which can eat 1,200 or more of them in a year. They hunt within a one-kilometre radius when food is abundant and they are not territorial, so nest boxes can be placed close to each other — 100 metres or so apart.


Once a breeding barn owl pair takes up residence, farmers report reduced rat and vole problems on their farms, and sometimes there are fewer pigeons and starlings in farm buildings as well.


Nest boxes should not be installed within 500 metres of major highways because they tend to fly low when hunting, so are at risk of being hit by vehicles when crossing roads. Optimal barn owl habitat is rough grassland in either blocks or strips along fields or waterways, particularly with a deep layer of old grass at the base where voles will hang out. The Townsend’s Voles that damage blueberry fields like moist grassy fields and sedge meadows nearby. Voles have very small ears hidden in their fur and are chocolate-brown and 11-14 cm long, not including the tail.


JUDIE STEEVES


Sofi Hindmarch is coordinating the placement of barn owl nest boxes.


They have short tails, four to seven centimetres, and they run on the ground.


Although also common in blueberry fields, the smaller shrew and mole do not cause damage to blueberry plants. Hindmarch says a group of volunteers have been very helpful with the design and construction of nest boxes for barn owls, which are located on top of poles. Putting them up in trees tends to attract squirrels instead.


“Lots of farmers are very passionate about this idea,” notes Hindmarch.


The poles must be a metre or more into the ground. For more information about barn owls and the boxes, go to: barnowlsbc.ca


British Columbia Berry Grower • Summer 2018 5


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