Within the next few weeks, one more group of sounds will be added to the Yukon's spring chorus; the "ribbitt" and "kreeep" of frogs, and even a few toads, ringing out of wetlands around the territory.

If you are willing to spend a little time listening, you could help track how well these amphibians are doing here. Frogwatch-Yukon is now up and running and looking for volunteer observers.

Populations of frogs and toads all over the world have disappeared or declined, both in wild areas and developed ones. These losses worry many people as amphibians are known as "indicator species" that are sensitive to different types of environmental changes.

As most frogs spend time on both land and water, changes in either environment can affect them. Increases in UV radiation, chemical pollutants and habitat changes are just some of the factors that can harm amphibians.

Yukoners might not think of amphibians as a major part of the territory's fauna; after all, these animals cannot regulate their own body temperatures and must rely on the outside temperature to stay warm. But there are indeed four species of frogs and toads living in the territory.

Wood frogs -- the most abundant species -- are found farther north than any other amphibian in North America. In winter they can freeze solid for brief periods, and live at least as far north as the Yukon's Old Crow Flats.

The boreal toad and Columbia spotted frog live in the southern Yukon, where the extra insulation provided in areas with deep snow helps them to survive the winter. The boreal chorus frog is found only in the southeast Yukon, and is hard to spot at the best of times as it spends most of the summer underground.

Brian Slough, the Yukon coordinator of Frogwatch, says that all interested parties are welcome to help with this program, which is part of the Ecological Monitoring and Assessment Network's (EMAN) Observational Program.

Like other EMAN programs, Frogwatch is set up to track changes in populations over time. As very little is now known about amphibians in the territory, Slough figures they will need 20 years of data or more to track significant changes in the population.

The long-term picture is necessary because frog populations are seldom steady in number. "Frogs fluctuate almost randomly," says Slough. "Their breeding success can depend on spring snow melt and the amount of rain in the summer, so there are lots of natural fluctuations in the populations."

Frogwatch is intended to monitor frogs and toads during their mating season when they are most vocal. In places such as Ontario and Nova Scotia, Frogwatch volunteers conduct roadside counts to monitor frog populations.

"We cannot do that here as there are not as many roads with suitable wetlands along them," says Slough.

Instead volunteers will be asked to listen for calls in chosen locations and send their observations on to Frogwatch. In most parts of the territory frogs do not start mating until late April or May, and some species do not breed until early June.

However, there is one location where toadlets are probably already hopping about. Boreal toads living at the Atlin Warm Springs take advantage of local conditions and start breeding early.

"It is a really unique population," says Slough. "They hibernate underground near the springs where it is probably quite warm, so they must naturally come out of hibernation quite early. Tadpoles can be present by early March."

Different species of frogs have their own distinctive mating calls, except for the male boreal toads living in British Columbia and the Yukon. They tend to be of the strong silent type and at most let out a soft "peep-peep" when other amorous males get too close.

You can hear the recorded calls of Yukon species by calling (888) 31-FROGS. Punch in #22 and follow the prompts. You can also hear the calls and find other information on the Frogwatch website at eqb-dqe.cciw.ca/emanops/frogwatch/yukon. Brian Slough can be contacted at 668-3295 or bslough@yknet.yk.ca.