A few years back, the annual musical at Interlochen Arts Camp was "Oklahoma!"
The Juniors all went to the dress rehearsal, and the next day, one of the campers asked, "Why do hawks make lazy circles in the sky?"
Understand that hawks hunt from the sky, so the higher they fly, the more area they can see.
Their eyesight is phenomenal. Apparently, birds of prey can see in the ultraviolet range of the spectrum, which turns out to be important.
Small mammals like mice and voles mark their trails with urine, and rodent urine reflects ultraviolet light. A hawk looking down on the land can just scan the ultraviolet trails and, from as high as a hundred feet, spot a rodent and swoop down for it.
But the lazy circles? Well, hawks take advantage of thermals - columns of warm air that form when the sun heats the earth unevenly.
Hot air rises, so when a hawk extends its wings, it can just ride the thermal up into the sky.
But if the hawk soars in a straight line for awhile, it could float right out of the column of warm air. So the hawk circles in order to stay in the thermal.
Riding a thermal is energy efficient and much easier than flapping wings. Most hawks take advantage of the "lift."
Hawks make lazy circles in the sky, and anywhere the wind comes sweeping down the plain, they help keep rodent populations in check.