How to count birds

Snow Geese flock, originally uploaded by topherous.

Cornell Lab of Ornithology’s eBird site has just posted Bird Counting 101. For anyone who spends time out in the field watching large flocks, whether they are shorebirds, waterfowl or hawks knows that estimating flock size can be ridiculously hard. Just looking at the flock of Snow Geese above is overwhelming if you want to try and estimate the number of birds. Estimating sizes of flocks can be biologically important because it is an additional data set that can be more useful than just knowing whether a species is present or absent.

Cornell puts forth several different tips for counting in their first installment:

  1. It is very important to write your observations down right away. No one can remember counts for 40+ species at a time. You will also end up second guessing yourself if you don’t write down what you see, particularly with the more common species, “Did I really see a Mourning Dove today or was that yesterdays walk?”
  2. Be conservative in your estimates, making sure you are not counting birds twice.
  3. For larger flocks, count a small portion of the flock and then extrapolate for the rest of the flock. For instance, count 10 birds in the flock and get a good idea of what that feels like. Then count the flock in 10 bird increments. This fall I was the counter on South Lookout at Hawk Mountain Sanctuary, PA on the morning that a flight of over 5,000 Broad-winged Hawks migrated through. I mainly counted in 5 and 10 bird increments because the birds kept coming and coming and coming.

One fascinating fact from the article was that we have a hard time estimating flocks when they are flying in 3D space. If a large blackbird flock is 100 birds wide, 100 birds long, and 100 birds deep, that is 1,000,000 blackbirds! I have a hard time imagining that.

Check out the full article.