Hippocampus may help homing pigeons explore

When researchers remove the brain regions, birds fly straighter on early parts of journey home

FLYING ON AUTOPILOT  Like automatons, homing pigeons without hippocampi fly straight toward home early in their journey, a new study finds.

Giuseppe di Lieto

Homing pigeons can find their own cozy loft from hundreds of kilometers away. A brain structure enables exploratory jaunts during the birds’ prodigious flights home, a new study suggests.

The results, published July 16 in the European Journal of Neuroscience, bring scientists a little closer to understanding how animals and people find their way in the world.

Sights, smells and Earth’s magnetic field may all help a homebound pigeon navigate. Along with other brain regions important for homing behavior, the hippocampus acts as a critical navigator, pointing out familiar landmarks near a pigeon’s home.

But the brain structure has another job earlier in the flight, ethologist Anna Gagliardo of the University of Pisa in Italy and her team found. The researchers loaded homing pigeons with GPS data loggers and released the birds from an unfamiliar place 19 to 30 kilometers away from home. Data from 33 pigeons showed that though the birds knew how to fly home, they often indulged in detours early in their journey, perhaps to familiarize themselves with the new area. Still, the pigeons maintained progress toward their loft, and as they approached home, the birds flew straighter.

Then the researchers surgically removed the pigeons’ hippocampi and released the birds in another new area. The flight plans changed drastically, data from 18 birds revealed.

As expected, pigeons without a hippocampus had trouble finding their loft when they got within about six kilometers. But their behavior early in flight was a surprise: After release, the homing pigeons without hippocampi flew toward home as if they were on autopilot, Gagliardo says. “They pick a direction and ignore what they’re flying over,” she says. “They don’t learn anything.” The little detours that normal birds take when flying over a new area were rare in birds lacking a hippocampus, the researchers found.

These birds on autopilot may suffer from “perceptual neglect,” in which they don’t notice features of the environment, Gagliardo says.

It’s possible that birds without hippocampi perceive their environment just fine but have trouble recognizing that places are new and responding appropriately, says neuroscientist Loren Frank of the University of California, San Francisco.

Work from Frank’s lab and from studies in humans has suggested that nerve cells in the hippocampus respond strongly to new things, he says. It makes sense that the hippocampus may behave similarly in homing pigeons. 

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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