Bernard Vonnegut. CHICKEN PLUCKING AS MEASURE OF TORNADO WIND SPEED

One way of estimating the wind in a tornado vortex is to determine by experiment what air speed is required to blow all the feathers off a chicken, a phenomenon known to occur in these severe storms. Hazen gives the following account of such an experiment carried out by Elias Loomis in 1842.

The stripping of fowls attracted much attention in this and other tornadoes. In order to determine the velocity needed to strip these feathers, the above six-pounder was loaded with five ounces of powder, and four a ball a chicken just killed. Professor Loomis says,

The gun was pointed vertically upwards and fired. The feathers rose twenty or thirty feet, and were scattered by the wind. On examination, they were found to be pulled out clean, the skin seldom adhering to them. The body was torn into small fragments, only a part of which could be found. The velocity was 341 miles per hour. A fowl, then, forced through the air with this velocity is torn entirely to pieces; with a less velocity, it is probable most of the feathers might be pulled out without mutilating the body.

Because it is difficult to separate the effects produced by the explosion in the gun from those that are the result of the movement of the bird relative to the air, this version of the experiment leaves much to be desired. With the modern technology of a wind tunnel or a shock tube, however, the difficulties associated with accelerating the bird to tornado speed could be obviated. In the course of an evaluation of a possible modern version of Loomis’s experiment, a preliminary investigation was made to determine what is known about the forces required to remove feathers. It was found that the force with which the feathers are held by the follicles is highly variable and in the circumstances of a tornado might be greatly reduced. It depends not only on the bird’s health and molting period, but also the state of its nervous system. A response known as flight - molt is recognized in which during conditions of stress the bird’s follicles relax so that the feathers can be pulled out with far less force than is normally required. Possibly this may be a mechanism for survival, leaving a predator with only a mouth full of feathers and permitting the bird to escape.

In light of the fact that the force required to remove the feathers from the follicles varies over a wide range in a complicated and unpredictable way and depends on the chicken’s condition and his reaction to his environment, the plucking phenomenon is of doubtful value as an index. Probably it is not indicative of winds as intense as might at first be supposed.

Acknowledgments

The author is indebted to Professor Kenneth Able of the biology Department of this university for his guidance to the scientific literature pertaining to this aspect of plumage.

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