Time for Nature

A fresh start for the northern leopard frog

April 28, 2008

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Waterton Lakes National Park of Canada

For decades, the distinctive northern leopard frog had been missing from Waterton Lakes National Park.
© Parks Canada, Cyndi Smith, 2007

For decades, the distinctive northern leopard frog had been missing from Waterton Lakes National Park of Canada . Now, at last, the frog is returning – with a little help from its friends.

In the spring of 2007, working with the Alberta Northern Leopard Frog Recovery Team, Waterton staff began reintroducing the frogs to the park. And it looks promising that the population has taken hold.

Finding the right pond

To encourage a new generation of northern leopard frogs to take hold in the park, researchers first had to determine whether suitable habitat still existed. Leopard frogs prefer ponds with lots of vegetation -- and no fish to eat their young. Park staff located the right kind of habitat in 2005.

The egg hunt begins

Then biologists needed to gather some eggs. This was easier said than done. There were no eggs to be found inside the park or on provincial land. Since the 1970s, leopard frog populations have waned across western North America. Finally the searchers discovered breeding populations on two sites, private land, in southern Alberta.

Fourteen thousand slim chances

Collecting eggs and counting the resulting tadpoles was time consuming work.
© Parks Canada, Dee Jessome, 2007

Biologists knew they could take up to half the eggs from each site without harming the source population. Each female produces up to 4000 eggs in a glob “about the size of a grapefruit,” says Parks Canada Ecosystem Scientist Cyndi Smith. Biologists collected these egg masses from 5 different females – 14,000 eggs in all.

They placed the eggs in protective floating cages to keep out predators. Then the cages went into the pond, and the waiting began.

Biologists carefully monitored the precious eggs, checking their condition and making sure the cages were intact. In a few weeks, the eggs began to hatch. Thanks to the protective cages, some 95 percent of the eggs produced tadpoles. Collecting all these eggs and counting the resulting tadpoles meant “a headache and a sore back,” says Cyndi. Researchers released the tadpoles from their cages, and the monitoring continued. At least 70 frogs completed metamorphosis from tadpole to fully formed juvenile. This may not seem like a lot of survivors out of 14,000 eggs, but developing frogs are vulnerable. They can be eaten by birds, predaceous diving beetles, fish and even grizzly bears .

A bright future?

Developing frogs are vulnerable to various predators.
© Parks Canada, Dany Boutin, 2007

The surviving frogs appear healthy and are dispersing to new habitats. However, it will take at least two years until the females from the 2007 introduction start to reproduce. From the 14,000 eggs released in the park, biologists estimate perhaps 20 adult females could reproduce.

Parks Canada will continue the reintroductions for at least two more years and monitor the population thereafter. But thus far, the signs are positive.

Helpful landowners

Cyndi Smith gives credit to the landowners who gave Parks Canada access to the eggs on their property. The reintroduction “couldn’t happen without conservation-minded private landowners. They’ve maintained suitable habitat so that we still have northern leopard frogs.”

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