Sunday, February 10, 2008

finding your way back home

A report in press from Current Biology gives the first evidence that birds (in this case Reed Warblers) are able to migrate by both latitude and longitude – something called bicoordinate navigation. Determination of latitude is reasonably easy, as orientation can be performed using either stellar or magnetic clues; but longitudinal orientation requires input of ‘time’ in some form.

Using Reed Warblers, as they are night time migrants and thus do not rely on visual clues, researches caught and displaced birds on spring migration from Rybachy to Zyenigorod (1000km east). Transporting the birds by air and mapping both geomagnetic field intensity and inclination (parameters of the earth’s magnetic field) they were able to show via caged experiments that the birds were able to orientate themselves onto a course that would take them back to their original destination; and they would not just follow a similar bearing to the one they were taken from i.e. on a course parallel to their previous movement.

This re-orientation in order to be able to compensate for their displacement - allowing them to reach their original destination - indicates that the birds can perceive longitude. How they do this is the next question to be answered. Currently the hypothesis rests on the suprachiasmatic nucleus (couldn’t find that in Svensson!) whereby the ventral core responds immediately to a change in time, whereas the dorsal shell lags behind. Measurement of the change between these two permits calculation of both ‘home’ and ‘away’ time permitting longitude to be calculated.

Image copyright of Steve Round: www.stevenround-birdphotography.com

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