EDMONTON - If it seems the birdsong in your backyard is a little quieter this spring, Jeff Wells is pleased you've noticed.

Wells, a leading American bird scientist, has been trying for years to get people to realize that the vast flocks of migratory songbirds that fill flyways from Mexico to the Canadian Arctic are not so vast any more.

"The birds are telling us something," said Wells, in Edmonton to meet with other scientists to discuss ways of moving the alarming decline in songbird numbers higher up the public agenda.

"With changes in abundance and changes in what they're doing, at the very least we should be paying attention to what that signal is."

The declines, most over the last 40 years or so, are striking.

Numbers of the striking yellow-and-black evening grosbeaks, found all through Canada's northern and western forests, have dropped 82 per cent. Four different kinds of sparrow have dropped by about two-thirds.

Even the ubiquitous boreal chickadee, the tough little bird whose song enlivens the bush even in darkest February, has declined by 73 per cent. And there are dozens of other examples.

Wells' problem is that even in the face of such steep drop-offs, there are still anywhere from 10 to 30 million birds crossing the U.S.-Canada border every night at this time of year. It's hard to generate concern in the face of that kind of abundance.

But that's no guarantee it will continue, Wells said.

Once, there were three to five billion passenger pigeons. Now, there aren't any.

"Everybody always said, 'They're fine somewhere else,' " said Wells. "They still had such an idea of abundance in their head that they let them disappear."

The culprits range from habitat destruction to climate change. Weather that warms up a week or two earlier than it used to offsets the delicate timing of eggs hatching at the same time insects are most available.

Birds range over such intercontinental distances that it's hard to pinpoint single causes for their distress.

"We're really just starting to quantify the threats," said Wells.

But there's no doubt about where the birds come from. The Canadian boreal forest, the immense belt of green that stretches uninterrupted and largely undisturbed through the northern reaches of virtually every province, is the hatchery for billions of birds every year.

Abundance matters, said Wells.

Birds tend return to where they hatched. If their numbers drop too far, they can get spread out over their range so far that it's hard to find mates.

As well, scientists still don't understand the role that the huge Canadian-born flocks play in ecosystems as distant as South American rain forests.

"It could be this massive abundance of birds is key to maintaining this tropical ecosystem," he said.

Canadians should realize the boreal forest is one of the last remaining large-scale ecosystems left on earth, said Wells.

"We've been striving to get this message out, that Canada has this global treasure."

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