Mys­tery of how tiny bird nav­i­gates to SA solved

Weekend Argus (Saturday Edition) - - FRONT PAGE - SHAUN SMILLIE

NEXT month a small non­de­script bird will be­gin touch­ing down in the coun­try af­ter a transcon­ti­nen­tal jour­ney that has lasted thou­sands of kilo­me­tres.

How this tiny bird finds its way to South Africa, of­ten to the same gar­den it left the year be­fore, has long been a mys­tery.

But now sci­en­tists be­lieve they have worked out, in part, how the Eurasian reed war­bler nav­i­gates and sus­pect it has to do with a ge­o­graphic map stored some­where in its brain.

The reed war­bler is 12.5cm-14cm long and ar­rives in south­ern Africa as a non­breed­ing mi­grant in Novem­ber.

To get here, the bird trav­els at night, chart­ing a course from its breed­ing grounds in Rus­sia.

For the reed war­bler to com­plete this jour­ney it has to over­come a prob­lem that has plagued hu­mankind for cen­turies – how to work out the vari­a­tion that oc­curs be­tween true north and mag­netic north.

Dr Richard Hol­land and Dmitri Kishkiniev of Ban­gor Univer­sity in the UK, who were part of an in­ter­na­tional group of sci­en­tists, be­lieve they have proven that Eurasian reed war­blers can work out this vari­a­tion.

They did this by plac­ing the birds in spe­cial fun­nel-shaped ori­en­ta­tion cages in Rus­sia.

“These birds will show be­hav­iour where they will hop around, and when they hop around in the mi­gra­tory sea­son, more of­ten than not it is in the di­rec­tion of their in­tended mi­gra­tion,” says Hol­land.

The sci­en­tists then ma­nip­u­lated the mag­netic field mim­ick­ing an 8 º vari­ance from true north. This vari­ance, says Hol­land, would have taken the birds on a route to Aberdeen in Scot­land.

They dis­cov­ered that the ma­ture birds tem­po­rar­ily ori­en­tated them­selves as if they were about to mi­grate to Aberdeen.

“It seems that a bird as unas­sum­ing as the reed war­bler, may have a ge­o­graphic map or mem­ory that en­ables it to iden­tify its lon­gi­tu­di­nal po­si­tion on the globe, only by de­tect­ing the mag­netic north pole and its vari­ance from true north,” says Hol­land.

“This, com­bined with other ex­ter­nal cues, which may in­clude the strength of the mag­netic field, star po­si­tions or smells en­ables it to lo­cate its cur­rent po­si­tion and ori­ent it­self dur­ing a long mi­gra­tion.”

The ju­ve­nile birds, how­ever, did not ori­en­tate them­selves to the new mag­netic sig­nal, which the aca­demics sus­pect might be be­cause this in­ter­nal map is learnt from ex­pe­ri­ence.

“We don’t know how this trans­fer hap­pens,” says Hol­land. “In their first year, they don’t re­ally know where they are go­ing, they just have this in­ter­nal drive that takes them

Eurasian reed war­blers can de­tect true north vari­a­tion

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