By JOHN NOBLE WDLFORD
Standing in the coastal shallows, its head and neck tilted at ■ sharp ancle, the peat blue heron appears to be listening to the wind or merely listing for want of anything better to do with a neck so long.
Actually, the pose is not Idle, and two Canadian zoologists now believe they have figured out the primary reason why herons and some other wading birds often tilt their necks while standing or walking slowly through the water.
It is not simply a way of scanning the waters for fish, the researchers concluded, or of estimating distances between their sharp-pointed bills and the darting prey. The tilted neck would seem to be the heron's way of overcoming a problem familiar to any swimmer on a sunny day—the glare from sunlight reflected off the water's surface.
Heron Rates the Cover
The discovery was reported in the April 20 issue of Nature, a British journal, by John R. Krebs and
Head-on views of herons
(b) on a sunny day. In (b) the bird Is tilting its head toward the sua to avoid glare.
Bnan Partridge of the University of British Columbia's Institute of Animal Resource Ecology in Vancouver. A
sketch of head-tilting herons even rated the cover of the journal.
During the course of a study of the feeding behavior of the great blue heron along the Pacific coast of Canada last summer, Professor Krebs and Mr. Partridge, a student assistant, observed the bird's characteristic posture.
The long-legged heron, which stands about four feet tall and is often mistakenly called a crane, was seen holding its long neck at an angle for minutes at a time. Then, suddenly turning its head, It would strike at a fish.
The head-tilting occurred far more often on sunny days, the zoologists noted, and only when the heron was facing at an angle to the sun —that it. not directly toward or away from it. The observers reported that herons "almost invariably tilted their heads toward the sun."
First, fish may try to avoid predators by swimming out of the bird's shadow and toward the sun. Thus, over a time, herons may have learned to lean out toward the sun and cut off the escape route. If that is true, herons should strike at fish most often immediately below their tilted heads—which the zoologists said is not the case.
Second, they considered a "glare hypothesis." If one stands in the water facing the sun at an angle, the sun creates a "patch of glare" on the water surface in Its own direction. By moving their heads, the herons shifted the glare patch out of their line of vision without leaving a promising fishing area.
Professor Krebs and Mr. Partridge tested this theory by training a hand-raised heron to hunt for fish in an indoor pool. The "sun" was a 500-watt floodlight, the only source of light in the room.
The heron tilted its head in the direction of the floodlight. As the light was moved, the heron moved Its head accordingly.
This led Professor Krebs and Mr. Partridge to the conclusion, as reported in Nature. that head-tilting seems related to glare and "presumably enhances the hunting efficiency" of herons in sunny weather.
rapidly making sure the wrists, hands, arms 57 and shoulders are limp and shaking loosely.
Rigorous loosening-up exercises are a deterrent to muscle-constrictions, cramps and soreness. Please do not let the fact that you feel like a ridiculous oversized chicken dissuade you from doing these exercises. In your heart you will know you're on the way to mastering the difficult aspect of the piratical frigate bird.
Next I will ask you to practice a particular swoop of the neck called the "Heron's tilt." (See Times article, p. 56.) This is a difficult procedure but necessary to avoid the direct rays of the sun which could ruin an important shot. The head and neck must be angled sharply to one side without changing the alignment of the throwing arm. The heron is able to keep this difficult position for minutes at a time, and with proper practice, human mastery of it is possible. This posture is especially helpful in avoiding glare on the surface of the water. The famous card-fishermen of Micronesia are particularly adept at this practice, and to watch them, sans sunglasses, pierce flying fish on a bright day in the Pacific is a joy to behold.
Once the body (yours) is warm and loose it is time to pick up the cards.
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