Toronto's reflective towers are lethal for migratory birds (source: NYT)

Toronto has a lot of glass-sheathed skyscrapers, but they have a sinister side. Reflective buildings are a serious hazard for birdlife and Toronto is in the top rank of the world’s most lethal cities.

According to this report in the New York Times, Casualties of Toronto’s urban skies, at least one million birds – but possibly as many as nine million – die from collisions with glass-clad skyscrapers in the city every year (H/T Matthew Kahn).

Toronto not only has a lot of crystalline towers forming a barrier along the north western shore, it’s also on “several migratory flight paths:

So many birds hit the glass towers of Canada’s most populous city that volunteers scour the ground of the financial district for them in the predawn darkness each morning. They carry paper bags and butterfly nets to rescue injured birds from the impending stampede of pedestrian feet or, all too often, to pick up the bodies of dead ones.

The founder of the brilliantly named bird rescue group FLAP (Fatal Light Awareness Program), Michael Mesure, says he once recovered 500 dead birds in a single morning. He took the NYT reporter to a particularly deadly building on the eastern edge of Toronto’s financial district and pointed to:

a gaggle of sea gulls sitting in trees across the street from an office building. They were waiting, he said, to dine on the smaller birds maimed or killed by the building.

The building has a glass facade that disorients birds by reflecting the surrounding trees. Perceiving the reflection as habitat, birds zoom at it full throttle without regard for the danger.

The victims are largely songbirds. Perhaps because of familiarity, the urbanites of the bird world, like house sparrows, pigeons and gulls, are much less prone to crashing into glass…

FLAP is taking legal action against the owners of two of the deadliest buildings. There’s a technical solution that involves applying a visibly patterned film over windows, especially on the lower levels where trees are reflected.

A German company, Ornilux, markets a glass with a pattern in the UV spectrum visible to birds but not humans. The company says bird strikes are the second largest cause of avian mortality after habitat destruction.

It is the reflective and transparent characteristics of glass that create a dangerous situation for birds. They see sky and landscape reflected by or on the other side of a window; the glass is not perceived as a barrier. To prevent these collisions, glass must be made visible to birds.

Mr Mesure says the danger to birds from reflective buildings is rarely considered by developers and architects. Complex or faceted reflective facades appear to be especially problematic.

I’ve no idea how significant bird strikes on buildings are in Australia (although I know Melbourne’s Western Treatment Plant is a destination for northern hemisphere birds), but there appear to be straightforward solutions. Creative designers could make them a positive.

Perhaps they could even look beyond the standard reflective facades to other forms (whatever happened to brise-soleil?).

The NYT points to a dilemma – one of the deadliest buildings in Toronto has historical value. It’s the last built work designed by Mies van der Rohe.

The urban smarts of sparrows, gulls and pigeons is intriguing. Do these species have attributes that enable them to adapt readily to the wiles of humans (like reflective buildings)? Or were generations of less wily ones simply wiped out over the last few decades (another form of adaptation, of course)?