Climate Change Ticks Ever Closer

On the Leslie St. spit, signs of global warming are being picked right from the feathers of migratory birds. And the ticks now spreading north carry with them the spectre of Lyme disease
Sep 01, 2007 04:30 AM
Hannah Hoag
Special to the Star

At the foot of Leslie St., a spit of land fans out into Lake Ontario. Over the years, the man-made peninsula, built with rubble from Toronto construction sites, has grown into an urban wilderness, home to butterflies, birds, rabbits and the occasional coyote.

The cottonwoods, birches, grasslands and bugs make the park popular with migratory birds that stop in to refuel on their flights – many coming from as far away as South America.

But lurking among the feathers of these international travellers are blood-sucking stowaway ticks that can carry Lyme disease.

Every morning before dawn during the spring and fall bird migration, Dan Derbyshire, co-ordinator of the Bird Research Station in Tommy Thompson Park, organizes a small group of volunteers who track the birds winging through the region.

The station is part of the Canadian Migration Monitoring Network, a string of sites across southern Canada and the northern United States that monitor the population trends of northern breeding birds.

From March to June, in 2005 and 2006, Derbyshire and his team of volunteer birders plucked ticks from the heads of the migrating birds. Then they mailed the ticks to scientists who are trying to gain a better understanding of how birds and climate change might increase the spread of Lyme disease through Canada.

"The number of cases of Lyme disease have been fairly low in Canada, until recently," says Nicholas Ogden, an expert in tick-borne diseases at the Université de Montréal in Quebec and a researcher at the Public Health Agency of Canada.

Since the 1970s, parts of the United States have suffered an epidemic of Lyme disease, mostly within the northeastern, mid-Atlantic, and north-central states.

In the United States, approximately 20,000 new cases are reported each year. The disease – which causes fever, headaches and can spread to the heart and nervous system if untreated – is rarely reported in Canada, but ranks among the top bug-borne diseases in the United States.

Ten years ago, eastern Canada had only two known populations of Ixodes scapularis, commonly known as the eastern blacklegged tick. Today, there are 13 or 14, says Ogden.

"It's not that those two have spread out, but that there are new ones bobbling up," he says.

They tend to settle in migratory bird landfalls, resource-rich chunks of land near large bodies of water.

Point Pelee National Park is one of the better-known migratory bird landfalls in southern Ontario. Each year millions of migratory birds funnel through this small spit of land that juts into Lake Erie.

But the Leslie St. Spit, the Toronto Islands and the Toronto lakeshore are also popular resting spots for migrants.

Like Point Pelee, the region lies within the crossroads of two major migration flyways. It provides weary-winged travellers a chance to rest during their migration over the Great Lakes and stock up on energy for the next leg of their travels.

"Toronto has always been on the migration highways," says Derbyshire. "There are lots of green spaces where the birds can drop in and rest, and the creation of the spit has really added to that."

Ogden says the migratory birds may be bringing ticks into Canada after passing through the northeastern and north-central states, where they're abundant. The birds may also be carrying ticks from established Canadian populations farther north.

Other researchers have previously found blacklegged ticks on migratory birds. "We just wanted to know if it was rare or a common thing," says Ogden.

Although Ogden won't reveal details of the study until they have been published in a scientific journal, he says all the stations from western Ontario to Nova Scotia captured migratory birds with ticks on them.

"We think migratory birds are quite efficient at spreading the tick around," he says.

But once the ticks are here, will they survive?

Canada's cooler climate once offered protection from the diseases of warmer regions. But as climate change brings milder winters, scientists worry that the ticks – formerly limited by the cold – may move farther north.

"Insects are cold-blooded – air temperature determines body temperature," says Jonathan Patz, Director of the Center for Sustainability and the Global Environment at the University of Wisconsin in Madison. The warmer air temperature can make it easier for the insect to survive the Canadian winter. It can also speed up the rate at which it develops.

According to the Ministry of Natural Resources, should greenhouse gas emissions remain high, average summer temperatures in southern Ontario are expected to be 4 to 5 degrees Celsius warmer and average winter temperatures about 6 degrees Celsius warmer before the end of the century.

"All the biological processes that are going on require a certain amount of heat," says Ogden. "If it is very cold, those processes are very slow or will stop altogether."

"When people say why should we worry about a half-degree of warming, it means everything to a mosquito carrying dengue or West Nile virus. It means do you have infectious mosquitoes after 10 days or three weeks?" says Patz.