University of Calgary researchers think they've discovered what's killing bats at wind farms in southern Alberta.

Researchers were finding up to 18 dead bats under each wind turbine, but the majority didn't show signs of physical trauma.

Team leader, Erin Baerwald, brought in the skills of Brandon Klug, who performed necropsies on the dead bats.

He found massive internal bleeding.

The researchers say the 40 metre blades create a low pressure zone that can spin upwards of 250 kilometres an hour.

Researchers believe the zone is concentrated to a small area around the blades.

Klug says it's a small change, but it's enough to kill the bats.

"So when you get in a situation where there's rapid changes of pressure on the outside the air inside the lung can expand so quickly, like it can't escape so it just expands the lung so quickly it just ruptures the capillaries around the lung and then you get a whole bunch of blood loss, and blood in the lungs and that's basically what drowns the bat."

Researchers say this could have an ecological effect as far south as Mexico because the bats are migratory.

Right now no one knows the full impact of the bat deaths.