BATS BATTLE BUDWORMS
Do bats adjust their diets during pest outbreaks?

by James Keller

The Douglas fir trees of southern British Columbia and the forestry industry may have found a natural ally to combat pests: bats.

Western spruce bud-worms eat needles off Douglas-firs, leaving the trees chewed up and bare. Extreme outbreaks of these pests can last up to 20 years.

Joanna Wilson, U of C master's student in biology, is studying the hypothesis that insectivorous bats may naturally feed on the budworm moths (the worms' adult counterparts) and may adjust their diet during these outbreaks.

Wilson's study is funded by NSERC, the Alberta Ingenuity Fund, the U of C and Bat Conservation International.

“I want to know if bats respond to the outbreak by coming in and feeding on the pest,” Wilson says. “So far, it seems that most of the bats actually change their diets so that in the first part of the summer – they're eating beetles and flies, but as soon as the budworm moths are out flying, they switch their diet almost entirely to moths.”

To see if their feeding behavior intensifies during outbreaks of the pests, Wilson is examining both the bat population and the bats' diet in areas of the forests with different levels of moth infestation.

The number of bats is measured with special equipment that can detect the level of bat activity in a certain area, while the droppings of captured bats are examined to determine their diet.

“My prediction is that bats come in and spend more time feeding in areas of budworm outbreak because there's so much food there, and that they might respond by including more moths in their diets.”

This could help control outbreaks by limiting pest reproduction. While it's the larvae that feed on the trees, a decrease in moths means a decrease in next year's larvae.

These pest problems aren't isolated to B.C. Wilson's research may have implications in Alberta and other provinces where there are closely related pests.

Wilson hopes her research can provide a solid answer when people ask ‘why should we care about bats?'

Wilson adds that the forestry industry does not intentionally harm the bat population, but that certain forest management practices can still have detrimental effects on bats.

“The bats really need the older trees and the dead trees for roosting, which sometimes get removed.”

Wilson's interest in bats took flight during her undergraduate degree, when she was face to face with one for the first time.

“A friend of mine did work with bats here at the U of C. …When he showed me one, it just piqued my interest.”

Wilson is taking that interest to the B.C. forests again this summer to collect more data. She hopes to finish her analysis this fall.