THE brightly lit skyscrapers of North American cities have always proved
irresistible to migrating birds, and huge numbers die every year after crashing
into them. But in Toronto their prospects are being made worse by local
seagulls, which have learnt to guide the birds towards the buildings so that
they collide with them. The gulls then feed off the corpses.
While city birds have learnt to avoid bright lights and reflective glass,
migrants 鈥渁re attracted to the light, then get trapped in the maze of the
buildings鈥�, says Michael Mesure of Toronto鈥檚 Fatal Light Awareness Programme
(FLAP), a volunteer group that rescues dazed birds from around the city鈥檚
skyscrapers every morning. 鈥淪ome collide with the glass, some drop from
别虫丑补耻蝉迟颈辞苍.鈥�
The seagulls, whose numbers are booming in inland cities, started by
scavenging the dead birds, says Mesure. 鈥淏ut as more gulls competed for food,
some learnt to drive birds into collisions.鈥� The gulls use the buildings as
鈥渢ools鈥� for gathering food, he says, herding the birds like sheep.
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Daniel Klem of the University of Pennsylvania calculates that lit-up
buildings and smokestacks kill 100 million birds a year in North America. The
carnage peaks during the spring and autumn migrations, when many species,
especially songbirds, fly at night and at low altitudes.
Coastal skyscrapers or those next to large lakes where migrants congregate
take the heaviest toll, says Mesure. The Sears Tower in Chicago, the tallest
skyscraper in the US, kills 1500 birds a year. And FLAP estimates that 10 000
birds a year die in the 70 hectares of Toronto鈥檚 financial district. The
most common are ovenbirds and white-throated sparrows, both in long-term
decline.
In the mid-1980s the CN Tower in Toronto, the world鈥檚 tallest structure,
started turning its floodlights off for eight weeks in the middle of each
three-month migration season after visitors complained about the bird carcasses
littering the ground. The number of deaths has fallen dramatically, says
Mesure.
FLAP is trying to persuade the owners of other skyscrapers to follow this
example. So far, the managers of 85 buildings in Toronto have agreed to ask
tenants to pull the blinds and turn off the lights. But Ken Hickson, manager of
the Canadian Imperial Bank of Commerce tower, says it can be hard to convince
tenants, especially law firms where people work night shifts, to pull the blinds
鈥渨hen they鈥檙e paying money for the view鈥�.