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Friday, April 15, 2005

Birds and Windows

What kills 5% of the bird population (1 billion birds) in North America each year? Plate glass windows. Birds see trees and sky reflected in them or a possible opening through which to fly, and crash into the glass and die of brain injuries (more here). It's a very serious problem, and today I had two experiences with the issue at work.

Last week I noticed a dead Mourning Dove on the window sill inside the barn where I park. I thought someone had found it and placed it on the ledge, but today I went and looked and could see the impression of feather dust on the window where the bird crashed into it. Apparently, the bird had been feeding in the open barn and tried to fly out through the bright window, only to crash and die on the spot.

Sometimes birds see their reflections in the window, and when they are feeling territorial, may attack their reflection. This afternoon a co-worker called me down to watch a Northern Cardinal repeatedly crash into the window of her office. The bird would perch in a bush near the window, look at the window, and fly directly at its reflection, falling to the ledge before hopping back into the bush and starting over again. While I'd heard about this behavior for years, this was the first time I'd actually seen it.

Both these behaviors can be reduced by cutting down the reflectivity of glass windows. It can easily be done with screening or by placing dots every 2 x 4 inches across the outside of the window (hawk or falcon shapes on the window don't really do it unless covering the window every 2 x 4 inches like the recommended dots). However, as long as people enjoy their clear window views, anything to break up the view is hard to sell. Interestingly, if bird populations were the stock market, how long would we accept 5% declines each year? Indeed, how long can we?


Anonymous said...

That seems like a ridiculous statistic. 5% of birds! 1 billion birds ?!? There are like 300 million people in the US and maybe what, 50 million households or more? How many of those, then, are apartments? And how many of these are in the cities as opposed to the country? I've lived in rural areas most of my life and a bird smacking into the window is a relatively rare occurrence -- maybe once every six months at most. It just seems rather unbelievable. Where'd you get that statistic?

Anonymous said...

The 1 billion number is an estimate from Dr. Daniel Klem Jr. of Muhlenberg College (Allentown, PA). The CNN article doesn't say what the basis for Klem's estimate is.

I've only witnessed a bird-glass collision once. I was sitting in 7th floor office in Fort Worth one day and heard a loud thump on the glass. I turned to look and couldn't see what made the noise. But I could see the feather-dust image of a Rock Dove wing on the window. Since the window had recently been cleaned, I had the pigeon silhouette there for months.


birdchaser said...

You can read some of Dr. Klem's research online here. The estimates are 1-10 birds killed for each building in the U.S., which may well be too conservative an estimate, as the two houses systematically monitored in this study reported 26 and 33 birds killed.

Anonymous said...

I have a friend who always makes fun of geologic time estimates: "Between 5 and 500 billion years ago..." Maybe I'm finally starting to relate. There's a huge difference between 97 million and 975 million birds.

The problem with that 20-30 birds on the monitored buildings is that there are a hell of a lot of buildings that will go centuries without a bird running into them. And I imagine the highest concentrations of buildings have the fewest concentrations of birds.

Didn't seem like the best research, but I imagine it's a good rallying point for bird-lovers. The most disappointing thing about the research is that the only alternative offered, really, is covering up your windows. That ain't gonna happen.

birdchaser said...

I agree that the range is a bit rediculous...because it is actually probably much higher than 97 million (1 bird/building/year) and may well be higher than 975 million (10 birds/building/year). While these were initial estimates, every time anyone has bothered to try and count the actual number of birds killed at a building, the total comes out higher than previously thought. Right now the claim that there are buildings that kill fewer than 1 bird/year is completely unsubstantiated, and all evidence points towards the higher end of the postulated range. Is there more research to be done? For sure. But for now, the 1 billion estimate is completely warranted by the best research available.

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