What’s killing the barn owls of the Fraser Valley?

Fraser Valley is home to most of Canada's barn owls, but the harmless birds' survival is threatened by factors such as rat poison.



Retired Chilliwack farmer Allan Peters had no idea that the rat poison he used around his former dairy farm may be harming local barn owls. But since local veterinarian Dick Clegg installed a nesting box in Peters’ old barn, Peters has grown protective of the charismatic, gold-coloured birds with a pale heart-shaped face that swoop at the rafters of his building.

The neighbouring organic vegetable farm has also seen its rodent problem vanish since barn owls started nesting in Peters’s old barn, according to Clegg.

Clegg has been working to protect barn owls in the area for over a decade. The Lower Fraser Valley is home to an estimated 250 to 1,000 adult barn owls, representing most of Canada’s population.

Recently, the species was upgraded from being of “special concern,” to “threatened,” reflecting a decline in numbers.

When frightened, barn owls screech and sway in unison, successfully intimating any predator or human that cares to look into their nesting box (see owlets hissing in video below). But these tactics can’t protect against the most common reasons for the species’ decline.

One is habitat loss. Barn owls love old cottonwood trees, but have grown fond of decrepit wooden barns as well. As these are torn down and replaced with modern glass-and-concrete structures, owls have fewer places to rear their young.

Another reason may be the proliferation of second-generation rodenticides, which Clegg believes to be the biggest killer of barn owls.

When rats eat poison from a bait box, they have about a week before they die, a deliberate lag to prevent them from figuring out that the boxes contain lethal material. But it’s during that time that rats are likely to be eaten by owls.

“The poisons now, what they call second generation, are much more potent. And they’re very insidious in that they stay in the environment a long time,” said Clegg.

Even animals that don’t eat rats, such as deer, have tested positive for rat poison.

“I find whole batches of owls in boxes like this, dead,” said Clegg, indicating the wooden nesting box high up in Peters’ barn. “Quite a few people around here know I’m interested in these things, and they’ll give me a call, and say, ‘I’ve got an owl in my yard. It’s walking around looking kind of weak. And, oh, it just fell over.”

Clegg picks up the dead owls and ships many to a research facility at Simon Fraser University. He has about ten in an office freezer right now waiting for shipping.

Researchers are still trying to figure out whether rat poisons directly kill owls. What they know, however, is that 75 per cent of dead owls tested by Environment Canada between 2005 and 2011 returned positive for rat poison in their livers. This is higher than the last testing period, 1988 to 2003, when only 66 per cent of owls came back positive.

Wildlife biologist Sofi Hindmarch, one of a handful of people studying barn owls in British Columbia, says that rat poisons may also have sub-lethal impacts on owls, such as affecting an owl’s ability to hunt or limiting its coordination, and thereby increasing the bird’s risk of being hit by a car.

The few adult owls and three babies currently nesting in Peters’ old barn haven’t caused the retired farmer any problems. Instead, they’ve been eating nuisance critters such as rats and starlings on nearby farms, adding to the raptor’s basic diet of meadow voles and mice. With the notable exception of enjoying blueberry stalks, the owls are harmless to most farming operations.

Clegg has installed about 120 nesting boxes over the last dozen years, and has heard multiple stories from local farmers that the owls have brought a rampant rodent problem under control.

“Just about anybody that’s got a box with owls in it, they’re very protective of them,” said Clegg.

Health Canada recently tightened its regulations on rat poisons, especially the most harmful, second generation ones such as brodifacoum and difethialone. As of Jan. 1 of this year, all rat poison products must be placed in tamper-resistant bait stations, rather than sold as loose bait. Rodenticides in meal, treated whole grain, pelleted and liquid forms have been discontinued by manufacturers since Dec. 31, 2012. Residents can still use their existing supplies until Dec. 31, 2016.

Clegg has recovered about 40 of the over 1,000 raptors that he has banded over the past decade, an effort he takes on voluntarily in order for researchers to gain a better understanding of the species. Most barn owls died young within a couple of years of birth, Clegg found, from being hit by a car. But whether that is related to ingestion of rat poison is anyone’s guess.

akonevski@theprogress.com
twitter.com/alinakonevski

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