[BirdPhotoIndia] Estimating: Sky Full of Black-Tailed Godwits

Dear Anand,

I generally use a grid method for these types of images. The way I go about it is as under:

I try to figure out how many birds occupy a certain part of the area by using grids and then extrapolate the count to come up with an estimate. We generally tend to underestimate numbers when they encounter large flocks because the birds are often closely packed in, and effects of distance and depth impact our ability to judge efficiently. And we don't do very well when counting in more than one dimension of space, under-counting being common.

Based on the grid system, my count is as under:

Total grids = 70 (see attachment)
Densely-packed grids = 57
Loosely-packed grids = 13
Avg. dense: (36+31)/2 = 33.5
Avg. loose: (4+6)/2 = 5
Total dense:57x33.5 = 1910
Total loose:13 x 5    =     65
Grand Total = 1,975, say 2,000

This is, of course, a very rough estimate but used to present the method, rather than calculate accurately. If the flock was flying in a line (like the other image that you posted), I'd count by increments.

Copying this to Bird Photo India as members as well as they may be interested in the discussion. 

BTW, please share the joke.

Cheers!

Sumit 

From: Anand Arya - GMail 

Date: Nov 18, 10:49 pm
Subject: Sky Full of Black-Tailed Godwits
To: delhibirdpix

What is the number ? Put some grids on the image and tried to do some  'estimates' - could be anywhere between 3-4000 Birds. (Caveat: I am not known to count correctly beyond 27.  But, that is another story)

Well,  I do not know how to estimate the number of birds in the image.  Can any one 'Consult' ?

Cheers.
Anand Arya
353, Sector 15A
NOIDA 201301
INDIA

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