My brother was helping out on a waterfowl count of Snow Geese. Being the rank amateur in the group he asked the head game biologist how he could determine how many birds were in a large flock. The biologist replied with a very straight face. " You count the wings and feet and divide by four."
I hope this brightens your day.
Actually I was at Bosque and a biologist was doing a count the about four thousand birds took off and he wrote down a number. No clue how they do it, must be a big time guesstimate !!!