The compasses of migratory birds
The earth’s magnetic field, the stars, the sun or the pattern of polarised light that is especially clear in the sky at dawn and dusk – these are compasses that birds use for orientation.
Researchers at CAnMove exposed birds from North America and southern Scandinavia to contradictory sensory impressions to see how they calibrated, or possibly reset, their compasses when the visual information from the sun and polarised light contradicted information from the earth’s magnetic field.
“Interestingly, we got different results from the Scandinavian and North American birds; the European birds did not appear to be affected by our manipulation, whereas the North American birds calibrated their magnetic compass,” says Susanne Åkesson.
“Interestingly, we got different results from the Scandinavian and North American birds”
In further experiments, researchers at CAnMove used specialised photoreceptors to study birds’ ability to register polarised light and magnetic fields. The measurements taken in the high Arctic show that the polarised light in natural conditions was considerably reduced under total cloud cover. It requires a sensitive sensory system to register such low levels – less than 10% – of polarised light, and it is still not known whether birds have such a sensory ability.
“We also carry out experiments in which we simulate changes in the earth’s magnetic field by magnetically transferring the birds between different places, in order to better understand how they navigate during their first, and subsequent, migrations. Young birds will be compared with more experienced adult individuals to determine how their innate abilities are affected by external factors such as the earth’s magnetic field,” concludes Susanne Åkesson.