Truth or Fic­tion?

BBC Wildlife Magazine - - Contents - FIND OUT MORE Sci­en­tific Re­ports: www. na­­ti­cles/s41598-018-27637-1

Do the stripes of a ze­bra ac­tu­ally help it stay cool un­der the sear­ing African sun?

Ze­bras may have the coolest pelts on the sa­van­nah, but that doesn’t stop them over­heat­ing, ac­cord­ing to new re­search. Their stripes are as mys­te­ri­ous as they are strik­ing; about 18 dif­fer­ent hy­pothe­ses have been put for­ward over the years to ex­plain their func­tion – rang­ing from cam­ou­flage to com­mu­ni­ca­tion to op­ti­cal il­lu­sions that de­ter bit­ing flies or cause car­ni­vores to mis-time their lunges.

Now, how­ever, bi­ol­o­gists from Swe­den and Hun­gary have nar­rowed things down, if only slightly, by rul­ing out an­other pos­si­bil­ity – that stripes help keep ze­bras cool in the sun.

The the­ory goes that the black stripes heat up more than the white ones, thus cre­at­ing lit­tle swirling vor­tices in the air above them, which keep air mov­ing across the fur re­sult­ing in a net cool­ing ef­fect.

To test whether this works in prac­tice, bi­ol­o­gists filled ze­bra-sized bar­rels with wa­ter, cov­ered them with ze­bra, cow and horse hides of dif­fer­ent shades and left them out in the sun. Un­sur­pris­ingly, the wa­ter tem­per­a­ture rose high­est un­der black pelts and re­mained cooler un­der white ones. Cru­cially, though, the black-and-white stripes did not keep the wa­ter any cooler than did uni­form grey pelts. SB

The evo­lu­tion­ary pur­pose of the ze­bra’s dis­tinc­tive coat re­mains elu­sive.

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