The Nature Writers of Texas

The best nature writing from the newspaper, magazine, blog and book authors of the Lone Star State . . .

Tuesday, April 14, 2009

Lords of the Dance
By Ron Smith
McAllen Monitor

The spring flock of sandpipers was spread across the South Padre Island beach in the rich evening light. There were perhaps a hundred or so, and if you were close, you would hear their soft sounds.

There were Westerns, Leasts and Semipalmateds, hungry and tired from their Yucatan hop, some scurrying along the edge of the waves looking for the little lives that they feed on and some snoozing peacefully with heads tucked into feathers.

But things are never very calm for long during migration. Abruptly, the entire flock exploded into the air, wheeled away, changing course again and again in perfect, swirling unison. The cause of their flight was a Peregrine Falcon, a lethal dark arrow hard on their tails.

The flock sped on an inline course to the north, and when no bird broke formation, the raptor veered right and flew back to his water tower perch. There would be more migrants and other chances.

A watcher might wonder how these sandpipers and other flocking birds make such en masse maneuvers without colliding. What bird takes the lead in making decisions about direction? How do they react so quickly?

It is well known that animals in a group are protected against attack because they can present a strong and united front. If one is ill or slowed by age, it will fall away from the rest and meet its fate. That's what predators like the Peregrine, the wolf or the lion wait for. Raptors are less likely to plunge into a swarming mass of bodies because of possible injury. A falcon, for example, is like a finely constructed craft..damage to a wing or leg could mean eventual starvation.

Other reasons for flocking include the availability of many eyes to watch for danger and also the usefulness of the familiar V-formation of geese in conserving energy.

To explain the coordinated flights, some imaginative people have posited electromagnetism or thought transference! (X-files music here) However, there have indeed been scientific studies of this phenomenon. One by Wayne Potts appeared in "Nature" magazine in 1984. (The Straight Several theories arose from the work. He used high speed film and observed frame by frame some interesting facts.

For example, there is no one "Commander Bird." Any individual can make the decision to turn in any direction, and the movement radiates through the entire group in a wave. It is not always the same bird. The best and safest move is toward the main body because birds which turn away are at risk of being separated from safety of the flock and caught by the pursuer.

The reaction of individuals to these changes can be as fast as 15 milliseconds! Potts turned to show business terms for his theory, naming it the Chorus Line Effect. For example, the Rockettes are aware of a leg kick beginning well down the line and react instinctively at the right moment.

It is very easy for an individual bird to create this wave just by flying into the group.
This then is how they avoid bashing into one another as they veer back and forth at such high speed. Individuals become aware of any random movement with such an amazing reaction time.

You can also see a similar phenomenon at the Monterey Bay Aquarium in California. Through glass displays, you watch large schools of silvery fish bank and swirl as if they had one mind in charge.

I prefer to go beyond the science and just delight in the pure beauty of this dance of flight. You can enjoy it even watching a flock of blackbirds coming in to roost at the malls or hospitals in McAllen! A northern experience could be observing hundreds of Snow Buntings as they rise over a winter cornfield like wind-driven flakes, fan out and then settle again to feed. On a Christmas Count in Ann Arbor, Michigan, my wife and I were once thrilled when more than a thousand of them fanned out over the Huron River.

Better yet, go to the island in the spring and watch the masters, the small shorebirds called "peeps." They are the true lords of the avian dance.