A northern toad’s health – yardstick for climate change

A northern toad’s health – yardstick for climate change
Canadian toad numbers are on the decline, but difficulties in measuring the population may have something to do with it.Photo John McKinnon.

The hibernating Canadian toad population in Wood Buffalo National Park appears to have diminished and researchers are hunting for answers.

For more than 10 years, a team of park staff has done an annual survey at two areas of sandy banks outside Fort Smith along Highway 5 to get an idea of what the population count might be. This is done by counting tiny holes left in the sand by toads when they emerge from hibernation in spring.

But this year the team encountered an unforeseen obstacle.

“This year when we went out, we couldn’t really tell how many holes there were because the bison had trampled the area,” said Rhona Kindopp, an ecosystems scientist at Wood Buffalo. “We counted fewer holes than the previous year, but that doesn’t mean there were fewer toads. The year before bison hadn’t been using that area.”

Kindopp said there may be other locations where toads hibernate, but they would be harder to access.

The number of holes counted since 2000 has varied, with the highest being 2,189 holes in 2001. Only 230 holes were counted this year.

While bison hoof prints are unique obstacles to tracking toad holes in the park, they are not the only ones, said John McKinnon, a resource conservation technician at Wood Buffalo who helped with the hole count.

“Buffalo, wind, rain – all are suspected to skew results,” he said.

Variations in numbers can also be linked to the survey’s timing. The toads begin emerging in April, with peak emergence in mid-May. This year’s study was done in early July.

Still, there is cause for concern that toad numbers are declining in Canada. According to Parks Canada data, amphibians have been declining on a global scale due to increases in ultraviolet radiation reaching the earth’s surface, habitat destruction, pollution, acid rain and climate change.

The Canadian toad is at the northernmost extent of its range in the park and, as such, serves as an important index for detecting the effects of climate change on the species.

“When something is at the extent of its range, it’s more sensitive to climate changes,” Kindopp said.

Also of interest is the way these toads hibernate. After hibernation, the toads disperse widely throughout the wetlands, but return to the same sandy banks for the winter.

“There aren’t a lot of documented places where toads hibernate together like that,” said Stuart MacMillan, manager of resource conservation at Wood Buffalo.

The Parks Canada team is currently talking about new methods of measuring populations, including, but not limited to, toads.

“You can use acoustics sometimes to monitor frog and toad populations,” said Kindopp. “So you put out recording equipment and get an index of the population by how many times you hear them call. We’re thinking of using that type of equipment to monitor wood frogs, which are another good indicator of climate change, but it would pick up calls of any species – birds, frogs, toads – that are calling. That might give us a better idea than the toad holes.”

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