Bird number estimation practice.

All,

I've been playing with Photoshop some more and came up with another
super-panoramic image of the Detroit River at the foot of Southfield Rd. in
Wyandotte (Dingle Park).  On the 30th of January there was
a large raft of Canvasback/Redhead Ducks that I photographed using the D300
and 400mm Sigma.  I stitched together approximately 30 images to produce
this image:  I performed some rough cloning on the top and bottom of the
image to fill in dead space so if it looks
a bit unnatural that's ok.

http://www.pbase.com/jourdaj/image/121761235/original

Now comes the challenge: I'm curious what kind of numbers you folks would
come up w/ trying to guesstimate the numbers of ducks/geese/swans in the
image.  Use whatever mental filters you have to get an approximate
number in 60 seconds or so.  Please respond off-line if you choose to
participate - I'll summarize results (leaving out names) and report back to
the list.

I tried this and came up w/ a number, which I'll reveal later.  I then took
the original, TIFF image I created (805 MB in size), blew it up, and
hand-counted every single bird in the image (don't ask me why....). I was
curious to see how good our perception
is at trying to determine large numbers of birds when we gather census
data.  How big is our systematic error?  I managed to get 90% accuracy when
I tried it.

Thanks,

Jerry
http://jerryjourdan.blogspot.com