Very Carefully !!
One of our jobs here is a weekly waterfowl census. That means that we count all of the ducks, geese and cranes that we can spot from the 50+ miles of roads here in the refuge.
In some spots the counts are easy, with a few dozen ducks here and there. But we do face more challenging circumstances as well.
For instance, first thing in the morning we park at a spot where Sandhill Cranes and Snow Geese fly out at dawn. We have multiple groups of birds flying over us as we try to get identifications and counts. Check out these pictures. Look at each one for a second or two and then estimate how many birds are in the groups. You can go back to look more carefully and check your count, but we can't because they are gone!! What we do is try to determine what groups of 25, 50 and 100 birds looks like. We then estimate numbers as they fly over. Teri does her count and I do mine. We then compare our totals and take the average. We never have the same number, but we are usually within 10% or so, which isn't bad! There have been around a thousand each Sandhill Cranes and Snow Geese passing over.
Another big challenge is big rafts of ducks floating offshore. One challenge is simply getting them identified to species. With wind, glare, and distance working against us, determining species takes a lot of staring into a scope!! The good news is that the ducks aren't going anywhere, but that is also the bad news. They stay way out there...
Here is a picture of a large raft of geese and ducks. Take your time looking at the picture, as these guys aren't moving. But you can see the problem. Once again Teri and I take turns at the scope, developing our own counts. And again, we average the totals. This group of Snow Geese and Redheads numbered about 7500.
Last year was much wetter, and they had total counts of over a million ducks. So while we are estimating groups of 50 and 100, last year's counters were estimating groups of 1000 and 10,000. We'll see if we end up with that "problem" as time goes by.