Overall, there's been a 12 per cent drop in bird populations since 1970, says the 36-page report, entitled The State of Canada's Birds 2012.
While some species have stayed at relatively stable levels over the last four decades — and some have even taken flight to a point — 44 per cent of Canada's 460-plus species have fallen in number, 66 of them so dramatically they are considered endangered.
"These declines appear to be largely due to lost habitat — breeding and wintering habitats," said Charles Francis, chair of the expert panel that penned the report.
But Francis said destruction of wetlands, grasslands and forests that are home to birds of all different feathers are occurring not only within Canada's borders, but also in countries where a multitude of species rest or overwinter during annual migrations.
At the top of the list of most endangered birds is the spotted owl, whose numbers have dropped to a mere "handful"; the burrowing owl; the whooping crane, which now number over 430 from a low of 15 in 1938; and the great sage grouse, with fewer than 100 males, down from thousands 20 years ago.
Populations of grassland birds, such as meadowlarks and bobalinks, have fallen by 45 per cent since 1970; some species who thrive in the long grasses of the Prairies or the farms of Eastern Canada are vulnerable, with numbers that have dropped by 90 per cent.
Birds known as aerial insectivores — basically such species as barn swallows, chimney swifts and flycatchers that snatch insects on the wing — are still relatively common, but have seen an overall descent in numbers of 64 per cent.
"What concerns us most about this group is we don't understand what the cause of the decline is," said Francis. "Is it different for each species or (is it) change in insect abundance, loss of habitat or climate change?"
It's difficult for scientists to come up with conservation programs for aerial feeders when they aren't sure what the causes are that need to be addressed, he said.
"A lot of our concerns around them are what are the insect populations doing," added Dick Cannings, senior project manager for Bird Studies Canada.
"One of the theories is that long-distance migrants evolved to arrive back in Canada at a certain time of year, and insect populations may still be healthy but they are peaking earlier in the year because of climate change," he said.
"So perhaps these birds are just out of synchrony with the insect populations and so are having trouble feeding their young. And so the bird populations are steadily declining."
However, the report shows there have also been successes in preserving or even increasing the populations of some species, notably waterfowl like ducks and geese, which on average have increased their numbers by almost 50 per cent in the last four decades.
Dave Howerter, national manager of Ducks Unlimited Canada's institute for wetland and waterfowl research, said Canada has an abundance of wetlands like bogs, fens and marshes that provide nesting and feeding sites for millions of ducks and other water birds.
In the last 40 years, the number of such aquatic birds as blue winged teals and the northern shoveller have risen substantially.
"Unfortunately, many threats still remain," Howerter said. "Wetlands continue to be lost. We estimate about 80 acres (32 hectares), or about 45 soccer fields are lost every day, and some waterfowl species are still declining ... So there's still lots of work to do."
Raptors, eagles and other majestic birds of prey whose numbers were decimated in the 1960s by DDT and other pesticides, are rising nicely, if not quite yet soaring. The species began recovering once DDT and similar agents were banned in the early 1970s.
"Across Canada, ospreys and bald eagles have doubled or tripled in population," the report says. "Thanks in part to some intense efforts at captive breeding, many major Canadian cities now have peregrine falcons nesting on skyscrapers and bridges."
Added Francis: "The recovery of these species demonstrates that where we take conservation action, where we ban pesticides and control pollutants in the environment and actively protect species, we can bring them back again."
But protecting birds takes a concerted and collaborative effort by governments, conservation groups and everyday Canadians, the expert panel members say.
And that leads to the question: why should Canadians care about birds?
"There are many good reasons to be concerned about this, even if you aren't interested in birds themselves," said Francis. "But the bird habitat is important to us, it provides ecosystem services such as clean air and clean water."
Birds are also — pardon the pun — like the canary in the coal mine when it comes to the environment.
"If bird populations are declining, that suggests that the state of the environment as a whole may be in decline," he said. "It was declines in raptors that signalled the problems with DDT and other pesticides and the big impact they were having on our environment."
Birds also enrich people's lives — think of the flash of a male cardinal's bright red plummage on a winter's day or the song of a warbler in spring — and are responsible for enterprises like recreational birdwatching, tourism and hunting, which together add billions of dollars a year to the economy, he said.
Cannings said it is not just scientists who compile bird population data, but an army of volunteers across Canada who take part in such programs as June's Breeding Bird Survey or the Christmas Bird Count.
"The efforts of all these enthusiastic birders have really made this report possible."
While bird species conservation requires a collective effort, both nationally and internationally, Francis said there are simple steps that individual Canadians can also take to help.
Consumers can buy only shade-grown coffee, instead of java produced on deforested South American mountain slopes that once gave shelter to birds, and beef raised on grasslands — not pasture — where birds can continue to live.
Lighted windows in both homes and skyscrapers on migratory pathways lead to the deaths of millions of birds each year, so lights should be turned off when not needed, he said.
Domestic and feral cats also kill hundreds of millions of birds every year in North America, said Francis.
"So keeping your cat indoors can protect millions of birds."