Climate control

When Stéphane Menu stepped into the sunlit landscape of a large forest fire burn near northern James Bay, a small bird caught his eye – a female eastern bluebird. At the time, Menu, a scientist with the Bruce Peninsula Bird Observatory, was with a team of bird atlas volunteers along the remote Ekwan River.

“I was quite proud of this one because, as far as I know, it might be the northern-most record [of this species] for all of North America,” Menu says.

Is the presence of a bluebird that far north evidence that the climate is growing warmer? The answer is unclear. Eastern bluebirds are found in open areas throughout much of Ontario’s boreal forest, and northern range limits for this and other species are often just conjecture, according to Menu.

Still, many naturalists are convinced that climate change is altering the face of bird life in Ontario. They point to northward range extensions for a number of other species. Northern mockingbirds, for instance, were found as recently as a decade ago mainly in southwestern Ontario and now have loudly inundated Toronto. Orchard orioles, which were once uncommon much north of Lake Erie, are a regular sight in London. Carolina wrens, considered at the edge of their range in the southern part of the province 20 years ago, have noisily announced their tenancy as far north as eastern Ontario.

“We know the planet is warming up, and birds are responding to this,” says Bridget Stutchbury, a professor of biology at York University.

Not so fast, counters Peter Blancher, a Canadian Wildlife Service scientist in charge of analyzing the atlas data. Blancher used the new bird records (from the southern half of the province, for which the records are the most complete) to test whether the ranges of most birds had shifted northward between the first atlas and the second 20 years later. Surprisingly, his conclusion is that they have not.

“When we looked at the evidence, you actually see more species shifting south than you see shifting north,” says Blancher. The finding is contrary to similar analyses done using atlas data in Britain and Finland. There, scientists found that bird ranges overall had moved north by an average of about 19 kilometres. Not so in Ontario.

“It’s related to the fact that the strongest influence on those birds has not been the shift in climate; it’s been the more pronounced shift in habitat,” says Blancher. “For example, the birds that rely on forest cover have been able to move into the south [because of reforestation across the southern part of the province].”

Peter Christie

“We didn’t really expect to find [Acadian flycatchers] in the wooded ravines,” says Martin, a former member of the national Acadian flycatcher recovery team. “You’re more likely to find them in large, more extensive forests – places like the big woods at Rondeau Provincial Park. But there they were. It’s encouraging.”

Indeed, the new atlas has good news for a lot of birds. “When you look at the atlas results overall,” says Mike Cadman, a senior songbird biologist with CWS who coordinated both atlases, “there are more species increasing than decreasing.” Seventy-four of the 302 bird species included in the atlases were significantly more likely to be found in atlas squares in the recent survey than they were in the atlas survey of 20 years ago. Forty species were significantly less likely to be found, and the remaining 186 bird species showed no significant change from the first.

Cadman, 52, is an enthusiastic man with an infectious curiosity about Ontario’s bird life. As a government biologist, he has had a hand in many songbird research projects over the years, but the two Ontario atlases have claimed at least some of his attention for much of his career. Working from donated office space on the second floor of the University of Guelph’s environmental sciences building, Cadman’s energy played an important part in propelling the atlas forward.

Many of the birds that appear to be doing better in Ontario since the first atlas are woodland species – birds such as thrushes and many migratory warblers that inhabit forests. The new atlas reports a whopping 36 of the province’s 93 woodland birds are significantly more prevalent now – more likely to turn up in an atlas square – than they were in the early 1980s. Only seven forest species show a significant decrease in this figure. But not all of Ontario’s birds are faring so well. Twenty of Ontario’s 35 species of grassland birds – such as bobolinks and eastern meadowlarks, which inhabit open fields, hedgerows and meadows – are now significantly less prevalent than they were during the first survey.

“This wasn’t a huge surprise,” says Cadman. “Prior to the atlas, there were already publications talking about reforestation throughout North America … There was already a suggestion that forest birds were improving as grassland birds were in decline across the continent. But we didn’t have a good sense of what was happening in Ontario.”

Cadman acknowledges that the atlas numbers point to something of a conservation trade-off. The apparent increase in forest birds at the expense of grassland species is a conundrum for environmentalists who want a range of healthy bird communities but who also cheer Ontario’s return to more natural forest cover. Nevertheless, says Cadman, some of the problems facing grassland birds also have a direct human cause: big, intensively farmed fields are reducing the amount of habitat available to birds that favour meadows and pastureland.

More puzzling are the atlas results that suggest that populations of swallows, nighthawks and other aerial insectivores are falling as well (see “Ariel foragers in decline”). For instance, each of the six swallow species that breed in Ontario was found to be significantly less prevalent in the second atlas compared to the first. The likelihood of finding cliff swallows in a square declined by half, as was the case with whip-poor-wills. In April this year, the chimney swift – found to be 46 percent less prevalent in the second atlas compared to the first – was designated as “threatened” by the Committee on the Status of Endangered Wildlife in Canada.

On the other hand, hawk, eagle and owl numbers are soaring. The prevalence of bald eagles is up 300 percent, merlins 134 percent and northern hawk owls a staggering 389 percent. Twenty years ago, Cooper’s hawks were found in 345 squares. At the time, the bold, bird-hunting hawks appeared on the National Audubon Society’s “blue list” of birds whose status was of concern. In the recent atlas, however, Cooper’s hawks were reported in 724 squares across the province and its prevalence has increased 1,218 percent in the Carolinian region alone. While the reasons for these increases remain unclear, there is certainly the suggestion that something is going right in the environment this species inhabits.

“Generally, raptors are one of the good news stories of the atlas,” says Cadman. “There are 26 species in Ontario, including the owls. Nine of them are showing significant increases and none are showing significant declines. That’s obviously great news – they being birds at the top of the food chain.”