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Thursday, August 8, 2013

To the roost

Tonight I was thinking about a friend who used to sit out in his yard at the end of the day and watch the sky for activity birds flying by, butterflies coming into roost.  I decided to give it a try.

It was a beautiful night.  The clouds were amazing and there was quite a bit of bird activity.  Not long after I sat down, I was a little shocked to see a Peregrine Falcon fly by.  This is my 9th year in this house, and that's the first Peregrine Falcon I've seen here.  Perhaps I should be sitting down to look up at the sky more often!

At about 7:20 p.m. I started to notice flocks of American Crows (Corvus brachyrhynchos). Sometimes it would just be a few birds, but other times over 20 birds flew by at once.  Here's the first group I photographed.  How many crows do you count in the image below?

(I counted 10 individuals.)

Flocks of crows continued to appear in pulses.  Occasionally they'd call, but mostly they'd fly by silently.  How many crows do you count in the next image?

(I counted 18 individuals.)

I kept watching.  And I kept counting.  At about 7:50 p.m. the background noise, i.e., all of the anthropogenic sounds, got noticeably quieter.  This made it interesting as I could then hear the wings of the crows as they approached and flew overhead.  How many crows do you see in the image below?

(I counted 9 individuals.)

I wrapped up around 8 p.m.  Although I didn't do a great job counting because I was also trying to take photographs, I counted at least 150 crows in about 40 minutes.  All of the crows were flying from the southeast to the northwest.  It appears that there is a communal roost somewhere in that direction!

Crow roosts may consist of hundreds to thousands (or even millions) of individuals.  The number of individuals in a roost increases after the breeding season and peaks in early to mid-winter.  Roost behavior has been studied in several locations.  In one study they found that most crows begin to arrive at the roost site about 30-40 minutes before sunset.  And in another they found that the majority of individuals have entered the roost site in the window that spans 10 minutes before and 10 minutes after sunset.

A few birds stopped briefly before continuing on.  I wonder where their roost site is?

I'm very thankful for a summer evening with shape-shifting clouds and surreptitious crows!

1 comment:

Purslane said...

I have occasionally seen a large cloud of crows spiralling over a tall cypress just east of the freeway in Petaluma, lots of gyres before settling down. Hundreds of birds. So many birds of a certain size seem to make a long commute every day from roost to feeding spot.