City Creek Nature Notes – Salt Lake City

September 20, 2016

August 22nd

Filed under: Cliff Swallow, Dragonfly, Insects, Meadow Mile 2.1 — canopus56 @ 11:17 pm

Circling Swallows

7:45 p.m. There is a meadow near mile 2.1. The meadow is in shadow, but about 25 feet above the meadow, the horizontal line of sunset is rising up the south canyon wall. In this sunset light and for a swath about three eighths of a mile long, fifteen swallows are hunting by flying in ellipses. Their orbits appear random, but after about five minutes, curiously, groups of five or ten swallows will meet in a small cluster in the sky. Then they will disperse into their individual ellipses. I watch them repeat this behavior two or three times. How they can time this is a complete mystery. Perhaps there is some explanation in mathematics of non-linear chaos. (For the mathematically inclined, the swallows are flying a pattern suggestive of Lorentz attractor.)

What the swallows are hunting is unclear. In the shadowed meadow, a few dragonflies also circle. Do the dragonflies eat small insects and then do the swallows eat the dragonflies? But there are too few dragonflies to support fifteen hungry swallows.

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