Caribou cluster in the thousands to flee mosquito bites during the hot Manitoba summer: study

Posted on October 23, 2024 by Peggy

A new study says caribou could start massing together in increasingly larger numbers during summers in Manitoba as the climate gets hotter — and mosquitoes are to blame.

Researchers at the University of Saskatchewan found the size of the Cape Churchill caribou herd during the migratory animal’s summer range in Wapusk National Park was positively associated with the local temperatures, peaking during the hottest days of the year in July.

Below 15 C, the animals normally form bands of between 11 and 12 caribou, said Ryan Brook, professor at the university’s College of Agriculture and Bioresources. But once temperatures rise over 20 C, hundreds or even thousands of animals can be seen pulling together to avoid harassment by hordes of parasitic biting flies.

“The idea is if you squeeze into this group and you’re crammed in between a bunch of others, then you’ve got less area available to get bitten,” Brook told Up to Speed host Faith Fundal during an interview Wednesday.

Up To Speed7:28Do caribou hate mosquitoes as much as humans do?

Ryan Brook, a professor of agriculture and bioresources at the University of Saskatchewan, tells host Faith Fundal how his team discovered that Manitoba caribou might feel the same way humans do about pesky mosquitoes.

“The Hudson Bay coast, that’s the largest wetland in North America.… There are incredible bugs like I’ve never seen anywhere else in my entire life. And so it becomes really, really bad.”

The researchers collected trail camera photos with temperature readings at the national park during the summer season between 2017 and 2020.

Brook said the animal’s travel patterns also change to account for the pests, moving against the blowing wind as much as possible to keep the biting to a minimum.

“You don’t want to be in the outside where half of you is sticking out. And so they push themselves into the middle,” he said.

“Imagine thousands of animals moving across the ground together in one tight group.… It looks like a swirling cloud on the ground. It’s really amazing to see.”

A female caribou - no antlers - walks across a wetland with Canada geese in the background. — The study predicts more frequent and large caribou groups as global temperatures rise. (Matthew Van Egmond/Parks Canada)

But while the large groupings may be beneficial in one way, Brook said it has a big drawback: The animals do not get to eat as much as they normally would when they’re clustered together.

“Caribou, they put on lots of weight and grow a new coat of warm fur in the summer so they can survive that long winter,” Brook said. “We worry that if this happens too much and the harassment lasts for too long, then they’re going to really suffer going into winter.”

The study predicts larger and more frequent groups as global temperatures rise.

Brook, who’s being doing field work up and along the Hudson Bay coast for 30 years, said one thing is certain:

“Biting flies are not fun at all, even with a head net and gloves and all the right gear,” he said.

“You take your hip waiters off at the end of the day of walking and you pour out, 2½ cups full of dead bugs … that gets a little old, and the buzzing — I mean, it drives people and animals kind of crazy.”