A well-known Yukon bird biologist says kestrels, the smallest member of the falcon family in North America, are rapidly disappearing from the territory.

Dave Mossop, a Professor Emeritus at the Yukon Research Centre, says the American kestrel population in Yukon has dropped by about 90 per cent over the past decade. He says the decline is about 65 percent in North America overall.

"This is a little bird that sits at the top of the food web in which it lives," he said. "And so, depending as it does on the whole system below it, it becomes a wonderful indicator species of things that are changing."

A group called the American Kestrel Partnership is compiling a database to study the decline.

Mossop retired after 25 years as the territory's bird biologist and has taken this project on as a volunteer.

Mossop and assistant Anne Aubin are checking about 100 bird boxes around the territory this summer. They've checked 80 so far and only found one with kestrel chicks inside.

Aubin said she's excited to be part of the effort to find out why the birds are disappearing.

"If they're disappearing and no one knows about it, then there's nothing anyone can do," she said. "But with our research, at least we're getting the word out and hopefully something can happen."

Mossop says two of the possible causes of the population decline are climate change or chemicals in the environment.