NORTHERN LEOPARD FROGS
Waterton Lakes National Park, Alberta
F ollowing the Kenow wildfire that burned more than 19,000 hectares of Alberta’s Waterton Lakes National Park in the late summer of 2017, the ground surrounding the wetlands where northern leopard frogs live was a “blanket of black,” says ecosystem scientist Kim Pearson. The frogs at this site had begun to breed that spring — the first time their mating calls had been heard since they disappeared from the park nearly 40 years ago. Efforts to return the species to the area had been challenging, and success only came as a result of Pearson tweaking reintroduction techniques over a matter of years. One of those tweaks may have been key — making sure eggs relocated from Saskatchewan’s Grasslands National Park to wetlands in Waterton Lakes had the same orientation to wintering grounds as their source populations. It turns out, frogs may have a genetic imprint that tells them which direction to migrate in spring and fall. Unsure of whether the frogs survived the fire, Pearson and fellow ecosystem scientist Barb Johnston set up monitors to detect breeding calls early in the spring of 2018. Pearson returned to retrieve the recorders in July, but confirmation that the frogs were alive and breeding on their own again was almost instantaneous. Within two steps around the shoreline, she spotted a large mass of frog tadpoles, and farther down, another. “We saw hundreds of them that day,” says Pearson. A later review of the monitor data confirmed several frogs had been calling for mates this past spring. Pearson was relieved, but not entirely surprised. “Following a wildfire, a lot of nutrients are flushed into bodies of water, including ponds.” One of those nutrients is phosphorous, an element that promotes the growth of algae — the favourite food of northern leopard frogs. In many areas, amphibian populations spike after a fire, she says. Pearson and Johnston plan to continue reintroducing eggs from healthy source populations to other sites in the park to help build genetic diversity. Northern leopard frogs are an at-risk species, and despite their resilience to natural processes such as wildfire, this population still needs all the help it can get.