Because hawks move, they may kettle more than once in different areas of the sky, and can be counted twice or 3 times if their flight direction after leaving the kettle isn't carefully monitored. Sometimes on busy days, it is very helpful to get a number of people counting the same kettle. Several people confirming numbers keeps the records accurate. I have learned over the years that once a kettle is found, it is necessary to scan out way in front of it to catch missed birds that have already flown off the top in the migration direction. Often while others are counting the kettle, I can pick up a string of birds that would otherwise be missed. I ususally count 1-from the first bird I can see way off to the west, back into the top of the kettle, 2- count the kettle as it streams off, and then 3-scan behind the kettle, (off to the east or NE,) to pick up stragglers, or new birds, flying into the thermal where the kettle had formed. All the regular counters have become pretty good with this and our numbers will often be identical or to within 2 or 3 birds. I ususally make a mental note of how many birds I counted out front of the kettle, for comparison to the number we come up with in the kettle. In this way I can know if there is any over count.
The birds that seem so small in the picture above picture, are far from the smallest specks we count. Often they are only specs in our binoculars - thus totally invisible to the naked eye. Think of how small a jet plane is in the distant sky. Then consider about how many small hawks might fit in that space flying around. It could be a couple of hundred, easy.
If all those hawks are moving around in a funnel shaped air shaft, they can't be accurately counted. Therefore, our best counts, when large numbers of hawks are kettling, is to count as the hawks fly away from the top of the kettle in the direction of their migration. When they reach the upper heights of what the funneling rising air will lift them, hawks set their wings and peel off. Usually from one to 4 or 5 at a time. Then they almost play follow the leader, generally following wind currents at that height. This is when we count them, if possible. Smaller kettles, we count down through the kettle. It takes a little time to learn how not to count birds more than once.
We are often asked, and asked ourselves in the beginning, "How do you count hundreds of birds." The answer is the same across the counting community. Ususally, by 5's. If it isn't possible to count by ones, capturing them in groups of 5's moves you through several hundred birds quickly. Counters in Texas, literally count tens of thousands by 5's using clickers, and not holding the numbers in their heads. They actually lay flat on their back to count as the birds stream through. they have a separate individual or two, who pick out individual birds from the thousands of Broad Wings, or which fly by their own paths.
Migrating Raptors, who gain lift from the rising funnels of air, may maintain that altitude on rising air currents for a very long distance. They use the lift to help not use their wings as much as possible. However, when the air is not providing long stretches of lift, we have seen them fly of the top of a kettle, where air is rising and begin a rapid desent over several thousand feet. If we have time to watch them all along their path on these days, we will see these birds seeking new funnels of rising air all along their path.
