Nocturnal Migration over Pittsburgh - September 26, 2010
Listening to nocturnal migrants is one of my favorite aspects of birding, almost a downright obsession these days. So
is watching migrants pass in front of the moon as they wing their way south in the darkness.
Photographing birds, as is well-known, is another favorite activity of mine, and no doubt a chronic obsession at this
For a few years now I've been trying to combine these activities, but have always come away discouraged. On the few occasions
in past years when I've actually managed to be outside on a night of a full moon *and* a large passerine migration, my camera
(or its operator) proved to be too slow, too blurry, too noisy, whatever.
But having recently acquired a new toy with superior high ISO performance and the capability of 10 frames per second,
I finally hit the jackpot.
The migration was ON on the night of the 26th. Birds were audible pretty much constantly for three hours on end (as usual,
most were Swainson's Thrushes). And, best of all, they were zipping in front of the moon frequently. The 1DMkIV has an
HD video mode, and I did take several videos, but I wanted high resolution stills as well. Even with a fast camera, this can
be a chore, and patience is the name of the game. So I sat with a cable release in one hand and a spotting scope in the other,
growing colder and colder over the course of 90 minutes as the temperature dipped into the low 50s. Finally, at exactly
the stroke of midnight (camera time), one bird at last made a fairly slow (one second, total) transit of the lunar disk. I
was at the ready, and fired off a sequence of 10 frames:
|Canon 1DMkIV, 500mm f/4L + 2x, 1/1000 sec. at f/8 (manual), ISO 1000, tripod, 10 frame composite
The image above is a composite of the 10 frames (done manually... what a pain). There was a slight haze across the moon
which served both to soften the overall image of the moon and darken the image to the point that even at ISO 1000, I needed
to "push" the exposure +2.5 stops in post processing. But the bird was sharp, which is what counts, and needless to say, this
was the most satisfying image of a bird in front of the moon I've made in 6 years of trying.
The camera takes 10 frames per second in high speed mode, so the total time shown in the composite image is just one
second. One side benefit of the haze is that it allowed me to "see the birds coming" from farther off the disk than normal,
since I could see their silhouettes in the haze and not just when they were in front of the moon. This is the only reason
why I had time to react and finally capture the high-res stills I had tried for years to make. Still... I'll be trying again
on a perfectly clear night, to get the moon completely sharp too. Photographers are never satisfied. The day we are is the
last day we ever pick up a camera.
|100% crops of three original images from the composite above
Now, for those of you inclined to ID every bird you see, the three images above are 100% crops (180x120 pixels each)
of three of the original ten images that made up the composite. If you want take a guess at what species this is, contact
me at firstname.lastname@example.org
OR, just scroll down...
...a little more...
You see the white head, dark body, and large, broad, rounded wings?
It's an adult BALD EAGLE.
This photo and the one below are two of the original 10 frames from which I composed the composite image at the top of
this page, upsampled 300% and further adjusted for brightness and contrast. Even after this processing, you can still only
barely make out the white head and tail, but hey, the picture was taken at midnight with the bird strongly backlit by a full
moon. One thing's for sure: making an ID in this way would have been impossible with film.
Now, the title of this page and of my composite image notwithstanding, what in the world was this eagle doing flying
around at midnight? There is nothing that I and others considerably more knowledgeable than me can find in the published literature
about Bald Eagles migrating at night. Of course, it didn't have to be migrating. Maybe just out for a midnight cruise?
I am working on making out the bird's altitude and distance from the camera based on the known position of the moon in
the sky (altitude and azimuth) and its apparent angular diameter as seen from earth at the time of the photo (also known),
compared to the size of the bird in the frame. There are some assumptions to make, and lot of room for error to creep into
these calculations, all of which I am still working out, but my preliminary results are showing that the bird was at least
2.0 km above the ground (possibly as high as 3.5 km) when the photo was taken, in the vicinity of the Ohio River at Coraopolis.
Flying generally south at midnight, two kilometers above the ground? If not migrating, then what?