I did another census of Chimney Swifts entering the chimney at Woodley Hills
Elementary School on 8-24-03. This school is very close Mt. Vernon in Fairfax
County.
This was a very different night from my normal observations. Usually when I
arrive (a few minutes before the official sunset) there is a small group of
birds circling the chimney which grows and grows until the sky is filled with a
swarm of circling birds. Then, as if someone hits a switch, they all start
funneling into the chimney.
Sunday night when I got there, there were only 20 or 30 birds circling the
chimney, but that really wasn't unusual because the numbers always start small
and seem to double and double and double every minute.
The strange thing about this evening was when this group of birds started
entering the chimney. There was still a very small group in the area (much,
much smaller than normal). I started to think that the recent cold fronts had
pushed all the birds further south, because when I did a count on 8/16 there
were 201 birds, and as has been typical for me, they were all swarming around
the chimney in a big group. On this night the small group that was there began
entering and in about 9 minutes, there were only 6 birds left in the sky.
At this point 106 birds had entered and only 6 remained in the sky, so my cold
front/migration theory was starting to make more sense.
A minute or two later, the number of birds had increased and it continued to
increase, and once again, birds started entering the chimney. The number of
birds in the sky never seem to grow into huge numbers, but as more and more
birds entered, the remaining bird number seemed to remain constant or keep
growing.
In 4 minutes, I had 150 enter. The next 3 minutes had 225 entering. The
following 2 minutes I had 125 enter and in another 2 minutes another 125
entered.
At this point there were only about 10 birds left in the sky, but again, like
before, this small number grew to just under 100 which entered in the next 5
minutes.
When it was finally over, 829 birds had roosted in the chimney.
All in all it was a very weird experience, almost opposite of a normal night!
Not nearly as dramatic as seeing 800 birds swirling around at once, but quite
surprising when I calculated the total......
829 on Aug 24th vs. 201 on Aug 16th.
Bart Hutchinson
Alexandria, VA
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