Decked out in his khaki-coloured outdoor vest, digital camera and butterfly net, Michael Mesure looks like a naturalist headed for a wilderness park.

But Mr. Mesure cuts an incongruous figure on his daily hikes around Canada's most urban of environments, the cluster of office towers in Toronto's financial district. While thousands of people stream by him each morning rushing to work, Mr. Mesure is patrolling the sidewalks and outdoor office plazas, net in hand, looking for the night's toll of birds that have bonked into the towers.

He's perhaps the world's only full-time, paid office-building bird saviour, trying to rescue birds from Toronto's scavenging rats and the indifference of many office workers who don't heed his simple message about turning lights off at night, the only action that seems to reduce bird mortality around tall structures.

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Mr. Mesure is pointing out the worst avian killing ground in the city core, the pedestrian passageway around the Toronto-Dominion Centre, the black architectural monolith that is one of the city's signature buildings.

"This is definitely the most lethal area we encounter," Mr. Mesure says, pointing to a site that has been nicknamed "flicker alley," after a woodpecker-like bird that has frequently been found dead here. "On a number of occasions, [dead birds]have just been blanketed across this area," he says.

The collisions are a serious matter. North America's office buildings and communications towers are silent killers. Strikes against structures, including windows on homes, are believed to kill 100 millions birds annually on the continent, mortality that may rank with habitat loss and the slaughter by domestic and feral cats in the steady decline of migratory song bird populations.

"I don't know any place in the country, on the continent, where there aren't examples of this," remarks David Willard, an ornithologist at Chicago's Field Museum of Natural History, who has studied the collision phenomenon.

When birds hit buildings, they usually don't die of broken necks, as might be thought on first glance, but suffer severe brain hemorrhaging due to the force of the impact. Collision survivors are often left disoriented and vulnerable to predators.

The distress calls of these injured birds often draws others closer to the buildings, leading to additional deaths.

Individuals and groups are working in many cities, including New York, Chicago and several communities in Canada, trying to reduce the needless avian death toll, accidents for which ornithologists don't have a totally definitive scientific explanation.

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But nowhere is the effort to save birds as embraced as in Toronto, where birdwatchers began monitoring the first large office buildings constructed in the 1960s for their unusual, and at the time, unanticipated ability to kill birds. Now the city has the most advanced effort in North America to study and reduce office-tower bird kills.

Part of the reason for Toronto's conservation lead is Mr. Mesure, head of Toronto's Fatal Light Awareness Program, known as FLAP. FLAP is bankrolled by a Toronto municipal foundation that supports energy-saving environmental projects, a conservation fund operated by Canada Trust, and by many of the property managers in the downtown core, where their buildings sport lobby posters urging people to be mindful of turning out their lights.

The group monitors bird collisions at 40 downtown structures, including the CN Tower.

Toronto building operators have become interested in ornithology for its pecuniary potential. Piles of dead birds littering sidewalks are bad public relations for property owners, while preventing bird deaths by turning out lights has become an unexpected way of saving money on electricity bills.

"You don't even have to embrace the ideal [of saving birds] They'll be making money regardless," says Gordon Menzies, the security supervisor at Toronto's Royal Bank Plaza.

Before the bank building started promoting lights out during the migration season "we used to pick up dozens first thing in the morning. It was terrible," Mr. Menzies said.

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Mr. Menzies said the efforts to save birds have touched many of his security guards, who develop an avid interest in the subject. "Some of them walk out of here with a minor in ornithology," he says.

Most nights during the fall and spring migrations, Mr. Mesure and other volunteers are prowling through the downtown core, beginning during the dark hours of the morning starting at 3 a.m., collecting the birds that have crashed into buildings and died.

On a more hopeful note, the group also gathers up survivors, before the stunned and disoriented birds are eaten by hungry predators, like seagulls and city rats looking for an easy meal. The birds, transported in paper bags, are taken to an aviary, complete with bird cages, that has been set up for this purpose in the basement of the Royal Bank Tower.

From there, survivors are driven to the city's humane society for treatment if they sustain injuries, or are released into parks if they they show no signs of lasting damage.

The dead are identified by species, added to the running tally the group keeps on fatalities.

The tall office towers in Toronto's financial district kill an average of 700 birds a year during migrating season, and injure even more, a death rate that seems typical of tall buildings. In a year, dead and injured birds from about 90 different species are collected, according to statistics compiled by FLAP.

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But the beauty of a bright, modern skyline of office towers at night, which inspires so many people, seems to be what transfixes birds and leads to their deaths.

At first glance, it seems unusual that birds would collide with the largest, and most obvious objects humans create.

But for reasons not entirely known, office building lights at night confuse the birds' natural navigation ability using the stars or moon. In the same way that humans walk into glass doors, birds have difficulty seeing windows.

The odds are high that migratory birds will encounter an urban area obstructed by buildings. According to research on building bird kills conducted by the World Wildlife Fund, the major cities of North America, if placed on one line of latitude, would occupy about 41 per cent of the continent's horizon.

That means there is a 41 per cent chance of a bird coming up from the Caribbean or Mexico hitting an urban area during migration.

To reduce bird deaths, environmentalists have had to fight the North American fascination with brightly lit skylines.

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FLAP, for instance, tries to battle it head on with the group's slogan, printed on its business cards: "big city, bright lights, dead birds."

To help dim the lights, Mr. Mesure takes pictures on his early-morning bird patrols, snapping shots of brightly lit Toronto office towers, typically at 3 or 4 a.m.

The pictures are used to show owners how their towers are needlessly burning up kilowatt hours of electricity illuminating largely unoccupied buildings.

"Many argue and say 'we can't be lit that much,' " he says, until he pulls out the picture to prove his point.

Mr. Mesure's worst bird kill in the downtown core was at the city's CN Tower, when over 100 died one night. "They were dropping like hailstones around us," he said.

When it comes to dimming lights, lawyers pulling late nighters are definitely the most heartless in the financial district, he observes. Building security guards, however, often betray more human decency, and frequently help in his bird-saving crusade.

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Of lawyers, "their attitude is: 'If I have to work at 4 o'clock in the morning, the last thing I care about is birds,' " says Mr. Mesure.