Perhaps they should call it the iPigeon. A new electronic gadget simultaneously measures brain activity and GPS-location of homing pigeons in flight.
In field tests published in a new study, a team led by Alexei Vyssotski at the University of Zurich used the device – actually named Neurologger 2 – to link brain activity to prominent landmarks used by the birds as they navigate.
Neurologger is really two devices: a miniature GPS unit fixed to the pigeon's back, and a 2-gram electroencephalograph (EEG), which measures electrical impulses in the brain, strapped to its head. Both feed data onto a flash memory card, which Vyssotski's team downloads and analyses after flight.
Initial tests of homing pigeons indoors identified several different bands of brain waves, connected to what the pigeons were looking at.
After Vyssotski's team released the pigeons 18 kilometres off the Mediterranean coast, activity in one particular frequency range plummeted as the birds flew across the featureless sea.
Brain waves in this band, however, perked up as pigeons neared the coastline, and when Vyssotski's team released pigeons in a city, the same frequencies spiked when the birds crossed prominent landmarks, such as highways.
Pigeons flying in flocks also produced fewer of these brain waves than pigeons flying solo. "When animals are flying in flocks it is not necessary to look at landmarks," Vyssotski says.
In some cases, the researchers noticed a spike in these medium-frequency brain waves as their birds flew over seemingly unremarkable terrain. It took a visit to the locations – a farm and a barn – for the researchers to realise that both housed colonies of feral pigeons that probably caught the eyes of their homing pigeons.
Brain activity at other frequencies also proved important to navigation. The highest frequency waves that Vyssotski's team recorded spiked when flocks formed at sea and when pigeon's changed the direction of their flight. Vyssotski thinks this band might represent the increased cognitive demand of landmark-free navigation, potentially using odour, solar, or geomagnetic cues.
Dora Biro, a biologist at the University of Oxford, UK, says Neurologger is "an amazing technical feat in its own right." But the device really shines because it opens up a window into the brain of navigating birds.
In the future, it will be interesting to compare how birds deal with novel environments versus familiar landscapes, she says.
Vyssotski's team, however, isn't stopping with birds. He recently collaborated with scientists in Panama to track the brain activity of sloths for five days – but they weren't interested in the navigational skills of the slow-moving mammals.
"We have found that sloths sleep, in fact, much less than was observed before in the zoo," Vyssotski says.
Journal reference: Current Biology (DOI: 10.1016/j.cub.2009.05.070)
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