How big is too big? How hot is too hot?

Those are questions Erin Miller plans to answer with her honours undergraduate thesis on bat boxes at the University of Calgary.

Miller, an ecology student, hopes her research conclusions will provide helpful guidelines for people who want to support local bat populations by building these structures.

Bat boxes play a critical role in the conservation of and research into Alberta's nine known bat species, one of which is endangered in Canada. 

Bat box Bowness Park

This bat box in Bowness Park has an open bottom to prevent guano, or bat feces, from accumulating inside. Excessive feces in a bat box can eventually drive bats away. (Erin Miller)

"Thinking about what a bat wants, what is gonna make them look at one box or another one and decide to occupy it?" asked Miller. 

Factors like the height of the box, its placement and its exterior colour could all make one home more attractive than another, she said. 

"Dimensions are a huge part about bat boxes. They have to have some good vertical height, because on a hot day ... the top of that bat box could get 35 to 40 degrees. Having that vertical height means that they can go down to cooler temperatures if need be."

Bat box temperature logger

This bat box is equipped with a temperature logger. It the box becomes too hot, bats will be unlikely to stay. (Erin Miller/CBC)

Avoiding 'ecological traps'

Another question Miller hopes to answer is whether bat boxes can provide suitable conditions for bat mothers and their young pups.

Miller said there's little research in this area, but that it's a critical component of any long-term conservation strategy.

"We might be putting bat boxes up and think, 'This is great, we're helping,' but we could actually be harming them," she said.

"This could become an ecological trap. What that is, is a bat sees a box and thinks, 'Oh, this is awesome,' but it might not have the conditions in which they can reproduce."

Erin Miller U of C bat box

Erin Miller examines a bat box in Bowness Park as part of her research for her undergraduate honours thesis at the University of Calgary. (Caroline Wagner/CBC)

Miller said her ability to study the impacts of bat boxes on maternal colonies depends on whether or not any pregnant bats actually choose to roost there. 

"We could come out of this and say, 'None of our boxes had maternal colonies,' because maybe they are just that extra bit anxious and timid about this, and they just need the attics that they're usually using."

Scoping out the territory

Miller will spend her summer observing bat boxes across Calgary, waiting for cover of nightfall to begin her exit counting — which is exactly what it sounds like.

Picture Miller, sitting in the dark a few feet away from the mouth of a bat box, counting the nocturnal mammals as they fly away.

At a bat box in Bowness Park, Miller has observed both the big brown bat and the endangered little brown myotis. The latter, which often roosts in buildings, is at risk because of the spread of white-nose syndrome.

The disease causes white patches to grow on bats' noses and wings. It has killed more than six million bats in 28 U.S. states and five Canadian provinces since it was first discovered in eastern New York in the winter of 2006-07.

Miller has also partnered with the Alberta Community Bat Program. The organization is taking specific measurements at bat boxes as far as Lacombe so that Miller can add them to her research sample. 

'Plan B'

Bat boxes are a type of "plan B" to provide bat populations with a suitable environment in places where logging and deforestation have occurred, said Miller.

Old forests with trees on the "edge of dying" provide ideal habitat for bats, because bark begins to peel away from the trunk, providing ideal crevices for bats to hang out, explained Miller. 

"Bat boxes can be that plan B. It shouldn't be plan A, but it can be the alternative if logging has occurred and we need roosts for bats."


With files from Caroline Wagner and The Calgary Eyeopener