No self-respecting 15th or 16th century explorer would leave home without one: magnetic compasses guided the great explorers as they voyaged into uncharted territory, and migrating birds are no different. Guided by two internal magnetic compasses – one that measures the angle of the magnetic field at the Earth's surface and a second which provides positional information – migrating species embark on voyages that can cover thousands of kilometres. But many less-adventurous species, such as chickens and zebra finches, are also equipped with a magnetic sense, which can help them to locate objects in their environment. Atticus Pinzon-Rodriguez and Rachel Muheim from Lund University, Sweden, were curious to understand more about the zebra finches’ sense of direction. Knowing that cryptochrome molecules in the retinas of magnetosensitive creatures are sensitive to specific wavelengths of light and are believed to produce a visual representation of the magnetic field, the duo tested the birds’ ability to locate a millet seed reward in a maze under different coloured light at high and low intensity as as the surrounding magnetic field was altered to find out whether cryptochromes also contribute to a zebra finch's sense of direction.
Recording the birds’ ability to return to the position of a pile of seed in a cross-shaped maze when the magnetic field had been aligned along one arm of the maze under green light (521 nm), the team was pleased to see that the finches successfully negotiated the maze. And when the duo retested the zebra finches in electromagnetic radio-wave smog – which is known to jam cryptochromes – the birds’ compass sense failed and they searched the maze randomly. The birds were clearly using cryptochromes to detect magnetic fields.
However, when they tested the birds’ navigational skills under blue light (461 nm), the birds were completely disorientated. Explaining that the magnetic compasses of many migratory species function perfectly in this shade of blue, Pinzon-Rodriguez and Muheim suggest that the difference could stem from the animals’ lifestyles. Many animals migrate at night by blue star light while zebra finches are active during the day, when other light wavelengths could disrupt the cryptochrome mechanism that guides nocturnal species. So, long-range migrants and stay-at-home species all seem to use light-dependent magnetic compasses, whether they are circumnavigating the Earth or hopping about in search of seeds.
