NEW HAVEN, Conn. — For years, Peter Brazaitis has enjoyed a symphony of amphibian love songs as he takes his nightly walk by the pond near his Harwinton home.

This seasonal parade of mating calls stays the same every year, starting in April with a chorus of raspy wood frog quacks, and ending in August, with the slow, resonating trill of gray treefrogs.

But Brazaitis got worried last May when he noticed the singsong trills of the American toad were largely missing from his nightly concerts. Was it an anomaly, or a worrisome trend?

“They spend so much of their life in the water, and they have soft, absorbent skin, so they are very sensitive to environmental change,” Brazaitis said. “They are our canaries in the coal mine.”

More data is needed before anyone can tell if Connecticut’s toad population is in trouble, possibly from habitat loss, pollution, or fungal infection, or if it was a one-time reaction to a hot, dry spring.

That’s one of the reasons why Brazaitis volunteers for FrogWatch USA, a countrywide research effort using trained armchair naturalists to collect data on declining frog populations.

The International Union for Conservation of Nature estimates that a third of amphibian species face extinction, a rate higher than that of any bird or mammal, due to habitat loss, infection or pollution.

Brazaitas relayed last year’s data on the decline in his local toads to chapter leader James Sirch at the Yale Peabody Museum of Natural History, who fed it into a national database.

Begun in 1998, FrogWatch USA trains thousands of volunteers in 106 chapters across the nation to report the mating calls of toads and frogs to develop practical strategies for their conservation.

The Peabody museum joined forces with Connecticut’s Beardsley Zoo to form Connecticut’s second FrogWatch chapter. The other one is run out of Mystic Marine Life Aquarium in southeastern Connecticut.

The Peabody-Beardsley chapter has trained 100 monitors so far in its first full year of existence. Before that, Peabody had trained frog watchers on its own through the program for three years.

Mystic has hosted a FrogWatch chapter for more than a decade, training hundreds who have monitored wetlands in the southeastern part of Connecticut, said program director Mary Ellen Mateleska.

You don’t have to be a herpetologist like Brazaitis, who once ran the reptile programs at the Central Park and Bronx zoos, to volunteer as a FrogWatch monitor, said Peabody’s Sirch.

Volunteers range from families who want to spend time with their children in nature, learning about science, to retirees who finally have time to pursue their hobbies, to armchair naturalists, Sirch said.

They must attend a training workshop where they learn to identify the mating calls of Connecticut’s 10 frog species. Volunteers have to be able to identify at least eight to participate.

They must also commit to monitoring a wetland of their choosing once a week for three minutes, about a half-hour after sunset, throughout the mating season, which usually runs April through August.

Gail Cameron, a Yale University manager, listens to the toads at a pond she owns with her sister near her Hamden home. For her, it is a peaceful moment often shared with her boyfriend.

Although the monitoring only takes three minutes, a monitor can’t simply walk up to a pond and start his stopwatch, because the mere presence of an observer often scares the frogs into silence.

“It forces you to be still, to be quiet, to focus and really listen,” she said. “It is a lovely little ritual that helps me reconnect with nature after a busy day. … I like that I’m doing my part, too, to help.”