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sun navigation


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The use of information about the position and movement of the sun for navigation. Provided with information about the time in location x, and observing the sun in location y, and animal would have enough information to work out the relative positions (latitude and longitude) of locations x and y. In the northern hemisphere, if the sun is later in the day at location y than it would be at location x at a particular (known) time, then y must be west of x, and vice versa. If the sun is higher in the sky at noon at location y than it would be at x, then y is south of x, and vice versa. In theory, the sun (provided the time at location x is known) provides sufficient information for bicoordinate navigation, but there is no conclusive evidence of these abilities in animals. There is evidence that navigating birds use the sun and stars as a compass, but a compass alone is not sufficient for bicoordinate navigation. Similarly, there is evidence for use of a magnetic compass by animals, but this alone is not sufficient for bicoordinate (i.e. map and compass) navigation. Despite much research, there is no convincing evidence for the use of a map analogue by animals.

Solar information gained on an outward journey can be used to navigate during the return journey. For example, Cataglyphis ants of the Sahara desert navigate by path integration. While foraging away from home, they continually measure all distances covered and all angles turned, and integrate these linear and angular components into a continually updated vector that points towards home. Cataglyphis uses a compass to monitor the angular components of its movements. This compass utilizes the pattern of polarized sunlight in the sky, as do some bees. The photoreceptors in a particular region of the ant's (and bee's (Apidae) eye are sensitive to directional oscillation of this pattern. The pattern of polarization changes with the elevation of the sun above the horizon. The ant is equipped with a neural template that resembles the polarization pattern when the sun is at the horizon, but differs from it for all other elevations. The best possible match between the template and the external pattern is achieved when the insect is aligned with the solar (or anti-solar) meridian. As the animal rotates about its vertical body axis, the match decreases systematically. The best match gives the zero point of the compass, and this deteriorates as the ant selects other compass directions.

Subjects: Zoology and Animal Sciences.


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