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Alarm Calls - Heard Round the WorldAmbience: Alarm calls, mobbing, Stellar's Jay, Black-capped ChicadeesGreene: The woods had been absolutely silent before then. And immediately the woods erupted at some distance with a chorus of alarm calls and birds were drawn from very far away in the woods. When birds spot a predator they make alarm calls to warn of the danger. And those alarm calls are recognized by more than just the bird's own species. I'm Jim Metzner and this is the Pulse of the Planet.Greene: Lots of species converge on the same alarm signals. It opens the door to many species listening in on each other. What's even neater is that in some ways this has occurred around the worldErick Greene is a biology professor at the University of Montana.Greene: So we could take an alarm call that we recorded here in Montana, if a hawk was flying over for ex, we could play it back in Virginia and the birds there would know exactly what that alarm call means. They would look up in the air and dive in the bushes. We could play that call in South America. We could play it in Africa, in Japan. We could play it in Australia. Birds around the world would understand exactly what that signal means.Because so many species of birds depend upon alarm calls as a protection against predators, scientists wonder if blocking alarm calls could be a way of controlling unwanted flocks of birds. Greene: If birds can't listen to other birds to cue into danger, they get really nervous and just leave the area. So one effective way of keeping birds away from airports might be in the future, of playing white noise to block this distant early warning system that's such an important part of their behavior.Pulse of the Planet is presented in part by Virginia Tech, inventing the future through a hands-on approach to education and research.