Weekend Argus (Saturday Edition)
Mystery of how tiny bird navigates to SA solved
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