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| One of the biggest hazards to birds in urban environments is window panes. |
One of the commonest injuries I see in birds are head and
neck injuries resulting from collisions with windows. Until recently I believed
this was an unfortunate but freak accident. But according to US scholar DanielKlem Jr at the Acopian Centre for Ornithology, the annual bird death toll due
to window strikes ranges from 100 million to 1 billion in the US.
“Clear and reflective windows in human structures of all
sizes in urban, suburban and rural settings are unintentionally killing vast
numbers of birds the world over,” he writes. ”Fatal strikes are possible wherever
birds and windows coexist.”
Of course there are other threats to birds – disease,
predation, starvation, adverse weather – but window strikes are often ignored
when it comes to assessing and addressing threats. To appreciate the scale of
the issue, Klem calculates that if you accept the most conservative estimate –
100 million deaths per year – you would need 333 Exxon Valdez oil spills each
year to match that level.
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| These birds pick up speed pretty quickly. |
He adds that predators such as cats may scavenge injured
or dead birds after window strike. In one study, 50 per cent of window strikes
resulted in fatalities and half of those surviving suffered some degree of
trauma or injury.
Why is it that birds behave as if window panes are
invisible to them? According to Klem, they simply don’t see them, or they see a
reflection of habitat that they’re trying to reach, or they may be drunk fromfeeding on fermenting fruits. Factors that increase the density of birds around
windows, such as perches, bird feeders, surrounding vegetation and artificial
lighting can increase the risk of window strikes.
The majority of strikes were associated with windows at low-rise
buildings (56 per cent) and private residences (44 per cent), while high rises
and skyscrapers – even with their massive windows – accounted for less than 1
per cent. Klem argues that such numbers probably reflect the fact that most
buildings are low rise.
Some species are more likely to suffer window strike than
others, but this still accounted for 28 per cent of species in the US and
Canada, and 9 per cent of bird species worldwide. In Tasmania, it is estimated
that 1.5 per cent of the 1000 breeding pair population of Swift parrots (Lathamus discolor) succumb to window strike.
Klem argues that, given the scale of this problem, we
need to transform window panes into something birds can see. This can be
achieved by angling window panes, retrofitting windows with one-way external
films or designing windows to incorporate UV signalling systems which are
visible to birds but not humans.
Reference
