Birds May Use 'Sound Maps' To Navigate Huge Distances
MELISSA BLOCK, HOST:
Now the curious case of the homing pigeon and the mystery of just how they do what they do: Navigate over huge distances to find their way home. We know they use the sun and the Earth's magnetic field. Well, Jonathan Hagstrum, of the U.S. Geological Survey, believes the birds also use sound maps. His study was recently published in the Journal of Experimental Biology. And he joins us now to explain how he thinks this works. Welcome to the program.
DR. JONATHAN HAGSTRUM: Thank you.
BLOCK: And your theory involves something called infrasound. Why don't you explain what that is, and how you think these homing pigeons use it.
HAGSTRUM: Well, infrasound is very low-frequency sound. And infra means it's below human hearing. So pigeons can hear down to 0.05 hertz, and humans can hear down to about 20 hertz. And what I think is going on is that there are waves in the deep ocean that are constantly producing acoustic energy. And that acoustic energy travels through the Earth as seismic energy, and then is reradiated at the landscape back into the atmosphere. And I think pigeons and other birds probably are listening to that reradiated infrasound, and using that to find their way home.
BLOCK: And how does that connect with what else is known about homing pigeons - as we mentioned, using the sun and the Earth's magnetic field - to figure out where they're going?
HAGSTRUM: Well, in order to get home from some location, you need a map and a compass. And we know what the compass senses are, in birds. They use the stars, the position of the sun and the geomagnetic field, as compasses. But what the big mystery has been for a long time - has been, what is the map? How do they know where they are relative to home, to set a compass bearing that they can then follow home?
BLOCK: Well, you started looking into why homing pigeons sometimes get lost. They can't find their way home. What did you find out?
HAGSTRUM: Well, I started looking into it because I read in the newspaper about some pigeon races in the eastern United States, where the birds were lost on a perfectly sunny day. And what I found out was that they - the races had been affected by the sonic boom off the Concorde.
BLOCK: The sonic boom off the Concorde.
HAGSTRUM: That's right. It would be very, very loud. But since it's traveled a ways in the atmosphere, all the high-frequency waves would have been absorbed. So only the infrasonic wave would have affected the race.
BLOCK: And once you started thinking about that and the effects of the Concorde, then what did you do to try to flesh out this idea?
HAGSTRUM: Well then, I was able to get a very large database of pigeon-release data from Cornell University; where pigeons had been released for 14 years, between 1967 and 1980. I was able to get a computer program that models how sound moves through the atmosphere, and I was able to get weather data for those days that birds were released all around the Cornell loft in upstate New York. And I started to run models of how the sound was moving through the air, and I was able to see that the pigeons were really being influenced by how the sound was coming to their release site.
BLOCK: So in other words, on days when the pigeons were really confused, when they were not able to find their way home, you could see patterns of something happening in the atmosphere, in the weather.
HAGSTRUM: That's right. When they could not leave a release site, I could see that the sound was not making it there. It was being bent up and over by the temperature and wind structure of the atmosphere. And on those days when they did come home, then the sound was making it to the site where they were leaving.
BLOCK: What do you think the implications are if your idea is - proves correct? What are the implications for animals, and for the planet?
HAGSTRUM: Well, it could mean that a lot of these animals - say, like whales or sea turtles, who swim across the ocean without any apparent problem; there are even birds that migrate from Alaska to New Zealand nonstop - I think they might well be using infrasound. And, you know, right about now, we use GPS to find our way around, and that involves satellites and a huge infrastructure to make that work. But there might be a way to do the same thing by just listening.
BLOCK: Well, Jonathan Hagstrum, thanks so much for talking with us.
HAGSTRUM: You're very welcome.
BLOCK: Jonathan Hagstrum is a geophysicist with the U.S. Geological Survey. We were talking about his hypothesis that homing pigeons use low-frequency sound to help them find their way. Transcript provided by NPR, Copyright NPR.