A once familiar urban dweller, Ontario’s latest official bird at risk is in free fall and global warming may be the key cause.
By Tim Tiner
Unlike most imperilled species, Ontario’s newest official bird at risk is a high-flying ace long familiar in the cities and towns of the province. In September, Queen’s Park declared the chimney swift a threatened species, six months after the federal government formally gave it the same status nationally. As swift populations plunge across eastern North America, researchers are racing to untangle the mysteries and misperceptions about this unique bird.
Migrants from the Amazon, chimney swifts are dark, long-winged, stub-tailed little birds that arrive in Ontario in late April and early May. When not tending to their nest, they are constantly airborne, swirling and chasing down flying insects on stiff, flickering, crescent-shaped wings. Swifts have tiny, weak legs but stout, strong claws, with which they cling to any rough vertical surface, bracing their spine-tipped tails against it.
These birds once nested and roosted primarily in large, broken-topped hollow trees, using their glue-like saliva to hold together their semicircular nests and paste them to the trees’ inner walls. As old-growth forests fell to settlement, swifts began to nest in chimneys – not used during the warm months – in the new homesteads. A chimney contains only one nest, but may also shelter nonbreeding swifts, including one or two “helpers,” sometimes offspring from the previous year, that in about a third of nests assist parents with nesting duties. Swifts also sometimes occupy air shafts, grain silos and the darkest corners of barns and abandoned buildings. After nesting and before and during migration from late July to early October, many swifts gather in bigger roosts, sometimes as many as hundreds in a single large chimney.
With the switch to gas and electric heating since the 1950s, however, chimneys have become too small for the sooty-hued birds. Old chimneys have been capped, wired over or lined with sheet metal, to which the birds cannot attach their nests. Most of the remaining suitable chimneys – largely on old churches, schools and commercial and industrial buildings – are also rapidly being closed, lined or demolished.
The Canadian Wildlife Service (CWS) estimates the provincial population of chimney swifts at less than 12,000 breeding birds, representing more than 60 percent of all Canadianswifts, which range from eastern Saskatchewan to the Maritimes. Their numbers are falling fast, though, especially in northern climatic zones where the rate of chimney deterioration and conversion is highest. According to the annual Breeding Bird Survey, Canada’s chimney swift population has declined by 96 percent since 1968, and decreases in Ontario over the past decade are close to 20 percent of the population each year. The Atlas of the Breeding Birds of Ontario (2001–2005) reported the species in only about half the number of locations in which it was found in the mid-1980s.
Surveys of remnant old-growth deciduous forest stands in Wisconsin and New York State report 18 to 20 large snags – potential swift nest trees – per hectare, which, by CWS reckoning, is more than 100 times the average density of chimneys in eastern North America a century ago. But very few such woodlands remain anywhere today, including Ontario, where less than 1 percent of the forest south of the Canadian Shield – where the vast majority of the province’s swifts nest – is more than 140 years old.
“If we preclude them from their current habitat, then they really have nowhere to go,” says Joe Nocera, a species-at-risk research scientist with the Ontario Ministry of Natural Resources (MNR). “It is our responsibility to manage them, because we have taken away their other habitat.”
The chimney swift’s troubles may extend beyond the loss of nesting space. Populations of many other aerial insectivores, from swallows to whip-poor-wills and nighthawks, are also declining. Biologists such as Nocera, who leads several MNR swift research efforts, suspect lack of food could be the leading cause.
“Probably some insects have declined dramatically, but we just don’t know. Historically, there’s no monitoring of insect species that aren’t important to humans,” says Nocera. While use of pesticides is suspected of being a key cause of their decline, he believes that many factors may be contributing to the problem. “If I had to throw my weight behind a theory, I’d say climate change has probably caused a mismatch in the timing of the birds’ needs and when certain insects emerge.”
Global warming may also be increasing the frequency of extreme weather events, the greatest cause of swift mortality. Heavy storms can wash away chimney nests and kill migrating swifts, while freak cold snaps or prolonged rains that keep insects out of the air cause starvation.
Determining the precise causes of chimney swift decline is remarkably difficult because the birds are so hard to study, being either in the air or hidden in inaccessible spaces. Nocera, however, got an unprecedented opportunity to examine historical changes in the bird’s diet last year when he discovered a pile of swift droppings more than two metres deep at the bottom of a power plant chimney at Queen’s University in Kingston. The accumulation bears distinct annual layers – like tree rings – of desiccated insect bits, that have been accumulating for some 80 years.
This year Bird Studies Canada (BSC) launched Ontario SwiftWatch, to collect observations of swift nesting and roosting from volunteers across the province. The project is largely based on work started in 2004 byNature London (formerly the McIlwraith Field Naturalists of London), whose members monitor more than 100 occupied chimneys, including half a dozen large late-season roosts. The group has tallied up to 2,500 swifts in a two- to three-day period.
Migrants seem to funnel into London as they head south, says Hazel Wheeler, a BSC project biologist, but much about the patterns, numbers and habits of these birds remains pure speculation. “They don’t call them swifts for nothing. They’re really hard to tie down and get a handle on,” she comments. “That’s why monitoring is very important for directing conservation strategies.”
MNR and CWS hope to use nesting observations to help them design artificial chimneys suitable for swifts in Canada’s climate. Many such towers have been successfully employed in the United States. So far, however, none of the 18 or so insulated plywood towers in Ontario, which volunteers in field naturalist groups have built over the past four years, have attracted any nesters.
Artificial towers may not be the ultimate answer, says Nocera, but might be an option for property owners closing off or taking down old chimneys. He foresees incentives for stewardship playing a big role in the swift recovery plan CWS is expected to launch, in conjunction with MNR, within the next two years. Under Ontario’s new Endangered Species Act, in the coming months MNR must also define the bird’s habitat and ultimately protect it. “This one is tricky, because it involves an urban [wildlife] resident,” says Nocera. “It involves more socioeconomics than other species.”
Tim Tiner is the author of several nature guidebooks and a long-time contributor to ON Nature.