When animals use celestial cues to navigate
In recent years there have been some spectacular astro-physical successes with the Cassini probe, the comet visit by Rosetta, the Pluto flyby etc. coming to mind. Successes, which were so fantastic that almost everyone must have heard of them. We do look at the stars and are fascinated by the world beyond our own. But animals, too, look at the heavens and see the stars, the sun and the moon – and many species actually make use of what they see up there.
For example, we all see the hand of the clock indicating the seconds ticking away; but we do not see the sun move and the minute and hour hands on the clock move so slowly that with one glance we also cannot see them move at all. It therefore may have come as a bit of a surprise when Canberra professor G.A. Horridge and co-workers announced many years ago that shore crabs could actually perceive the movements of the sun, moon, and stars. Since they can do that, the question arose whether that ability helped them navigate in an environment that is rather featureless, flat and devoid of landmarks; a beach or the intertidal zone for instance.
To be able to see the stars move may help, but it is, of course, no proof or guarantee for astro-orientation: sailors learn to recognize celestial patterns and use them in navigation and the Hungarian physicist Gabor Horvath believes that Vikings on their northern Atlantic cruises used a birefringent sunstone and the plane of polarized light to determine the sun’s position when it was occluded on cloudy days. In that way they could determine compass directions, North, South, etc.
Numerous experiments have shown that tiny migratory birds like the European robin or warblers, for example, which fly at night to avoid attacks by predators, are born with an inbuilt “map” of certain key stars of the sky that they can rely on as navigational aids. The Italians Pardi and Papi in the 1950s and thereafter Alberto Ugolini had been studying the amazing orientation behaviour of intertidal wolf spiders and beach hoppers: they too can obtain and use clues from the sky to tell them which way to turn if they happen to be blown or washed off course. And not only sunlight, but even under moonlight as Ugolini reported, the beach hoppers find their right direction.
Perhaps most surprising of all was the claim by the Ukrainian insect physiology group, headed by Prof. Frantsevitch in Kiev, in 1977 that the humble dung-beetle uses astro-orientation methods to travel in a straight line at night. Researchers of the Lund Vision Group around M. Dacke in collaboration with the South African researcher M. Byrne have shown that the African ball-rolling dung beetle Scarabaeus zambesianus possesses a solar compass and uses polarization vision when trying to find a suitable burying site for its dung ball during the day, but that the celestial compass that these beetles use is worst at noon. At night, however, some key stars of the Milky Way are sufficient to give them the directional clue they need. The fact that so many animals, big and small, keep an eye on the stars above their heads at night and gather information from so far away, clearly demonstrates that we humans, in terms of celestial orientation, are clearly not the “stars in the universe”.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
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