C in december when the annual rains had transformed

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cIn December, when the annual rains had transformed the roads into rivers, Hattie was,therefore, more than a little surprised when she checked the data sent by the radiocollarsshe fits to the zebras she is tracking to find that six of the harems were 270 km away onthe edge of the Makgadikgadi, a huge mineral-rich area where salt has collected over theyears as wate� evaporates in the heat. Then, when the last of the moisture from the rainshad disappeared in May the following year, five of those harems came wearily back to theOkavango. This raised the question: why, despite a plentiful supply of food and water, werethe zebras being drawn eastwards to the salt pans? Even more difficult to understand waswhat made six of the groups travel so far, while the other five remained by the Okavango.DThis discovery created quite a buzz in the research community. I decided to visit Hattieand she explained that a century ago the large number of Botswana's zebra and wildebeestherds and the resulting competition for grass made migration essential. One of themigration tracks went from the Okavango to Makgadikgadi. But in the late 1960s, giantfences were put up to stop foot and mouth and other diseases spreading between wildlife28u�'�'ultjf:?
Readingand domestic cattle. One of these went across the migration track. Though the animalscould get round the obstacle, each leg of their journey would now be 200 km longer - animpossible distance given the lack of permanent water on the extended route. Even today,with the fence gone (it was taken down in 2004), there is dangerously little drinking waterto support the zebras on the return journey to the Okavango.Ewww.irLanguage.comAs a zebra can live up to 20 years, the migration must have skipped at least one generationduring the 40 or so years that the fences were up. This prompts another question: it hasalways been assumed that the young of social herbivores like zebras learn migratorybehaviour from their parents, so how did the latest generation learn when and where togo? Not from their parents, who were prevented from migrating. Did they follow anotherspecies, such as elephants? We may never know.FHattie's data points to the conclusion that there are several zebra populations adoptingdifferent behaviour. The first, like the vast majority of the Okavango zebras, take it easy,spending the entire year by the river. The second group, 15,000-20,000 strong, worka bit harder. They divide their time between the Makgadikgadi salt pans and the BotetiRiver, which is reasonably near by. They sometimes struggle to find water in the Botetiarea during the dry season, often moving 30 km in search of fresh grazing. Their reward:the juicy grass around the Makgadikgadi after the rains. The final group of zebras, whosenumbers are more modest (though as yet unknown), must surely be considered as amongthe animal kingdom's most remarkable athletes. By moving between the Okavango andthe salt pans, they enjoy the best of both worlds. But the price they pay is an extraordinaryjourney across Botswana.

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