Birds May See Earth's Magnetic Fields

Birds can travel the world without any of the gizmos that humans depend on, and a new study suggests how: Our feathered friends might "see" Earth's magnetic field.
While other mechanisms are thought to help birds navigate, including magnetically sensitive cells within their beaks, their brain regions responsible for vision are in full gear during magnetic navigation, researchers said.
"If you look into the brain of a bird during magnetic compass orientation, only the visual system is highly active," said study co-author Henrik Mouritsen, a biologist at the University of Oldenburg in Germany, noting that most migratory birds do so at night. "Other regions of the brain are not, so birds could use vision to 'see' Earth's magnetism and orient themselves."

Mouritsen and his colleagues' findings are detailed online in a recent issue of the journal PLoS ONE.
Magnetic chemistry
The researchers previously discovered molecules called cryptochromes, which change their chemistry in the presence of a magnetic field, in the retinas of migratory birds' eyes.
"When light hits these molecules, their chemistry changes and magnetism can influence them," Mouritsen said. The molecules might then affect light-sensing cells in the retina to create images, which would help the brain navigate during flight, he added.
A direct connection between the specialized cells and the region of the bird's brain active during magnetic orientation, however, had never been shown before.
Mouritsen and his team recently found such connections between the cryptochrome-holding retinal cells and the "cluster N" region of migratory birds' brains, located in part of the brain responsible for vision.
"Cluster N is highly active during magnetic field orientation at night, when migratory birds fly," he said, explaining that non-migratory birds don't seem to use it during night flight. "We can't see what birds see, obviously, but they may pick up some sort of shading in their vision at night to act as a compass."
No smoking gun
Mouritsen noted that while the work is exciting, it isn't direct proof that they can actually "see" Earth's magnetism during migratory flights at night.
"If we could listen in on the neural connections between the retinal cells and cluster N, and show they actually send magnetically-influenced signals to the brain," Mouritsen said, "then that would be really compelling evidence that they can see it."
Even if migratory birds can see Earth's magnetic field, he noted, plenty of mysteries remain to explain their uncanny navigation.
"Birds also use the sun and stars to navigate, but we're not certain how," Mouritsen said. "How do they compute all of this information and end up with a direction to fly in? There are so many steps in this process we simply don't know about."

Cows Have Strange Sixth Sense

Researchers used Google Earth to find that cows tended to face north-south along the Earth's magnetic field lines while grazing or resting. Past research has shown that wind and sunlight can cause herd animals such as cows to change their alignment, depending on the conditions. CREDIT: Hynek Burda

A study of Google Earth satellite images has revealed that herds of cattle tend to face in the north-south direction of Earth's magnetic lines.

Staring at cows may not equal the thrill of spotting celebrities in public or rubbernecking at car accidents, but the researchers found nonetheless that our bovine friends display this strange sixth sense for direction.

Their field observations of red and roe deer also showed those animals facing toward magnetic north or south.

"Google Earth is perfect for this kind of research, because the animals are undisturbed by the observer," said Sabine Begall, a zoologist at the University of Duisburg-Essen in Germany and coauthor on the study detailed in the journal Proceedings of the National Academy of Sciences.

Wind and time of day did not offer better explanations for why 8,510 cattle in 308 locations around the world would mostly face north-south. Shadows suggested that many of the images were taken on cloudless, sunny days, so Begall's group also factored in direct ground observations of cattle herds.

A strong wind or sunlight on a cold day have typically proved more the "exceptions to the rule" that might cause large animals to face away from magnetic north-south.

The data on 2,974 deer came from direct ground observations and photos in the Czech Republic. Researchers also examined fresh beds left by resting deer in the snow, where the animals had sought shelter deep in the forest away from the wind.

Both cattle and deer faced a more magnetic north-south direction rather than geographic north-south, (Earth's magnetic poles do not line up perfectly with the North and South Poles).

Previous research has shown that animals such as birds, turtles and salmon migrate using a sense of magnetic direction, and small mammals such as rodents and one bat species also have a magnetic compass.

Begall and fellow researchers became interested in seeing if larger mammals possessed a similar magnetic sense, following up on coauthor Hynek Burda's work on African mole-rats.

"Our first idea was to study sleeping directions of humans (e.g. when doing camping), but there are too many constraints," Begall told LiveScience. "So, the idea arose to look for other large mammals like cattle, and Hynek was fascinated when he recognized that cattle could be found on Google Earth satellite images."

Google Earth's convenience also came with some downsides. The researchers had to estimate the date, time of day, temperature and wind direction, and could not distinguish between head and rear for many of the cows because of low image resolutions.

However, the researchers suggest that the finding of large animals' sense of magnetic direction could raise other agricultural questions, such as whether keeping cows in barns facing east-west might affect milk production.