Jan 28 2008
Last Friday outside my office window I noticed a steady stream of crows flying west-northwest into Oakland. They were coming in to roost.
I went back to the task at my desk but when I looked up again the stream was still there, still steady. Amazing.
I usually don’t try counting crows because I lose track but I remembered Dr. Tony Bledsoe telling me how he estimates flock numbers by counting the rate of birds during a given period of time, then measuring the time.
I picked a point of reference and set my stopwatch. 200 crows per minute. Now all I had to do was watch until the stream ended and check the rate of crows periodically.
I watched until it was too dark to see them. I checked the rate a couple of times and they still flew in at 200 crows per minute. Even after dark they kept coming, though the rate seemed to drop, but at that point I couldn’t be sure because they matched the sky.
From start to end, it was 70 minutes. 14,000 crows. And those were only the crows I could see! Judging by reports of crows elsewhere in Pittsburgh, the total number could be two or three times that.
In about a month, the flock will begin to disperse. In the past few weeks they’ve changed their start and end points, and anyone who thinks “as the crows flies” means a straight line ought to watch this flock. Even their flight path curves in the sky.
The photo is a Pittsburgh crow roost at dawn by Doug Bauman.
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