Using underwater microphones called hydrophones, the team was able to record the songs from whales up tens of kilometers away.
Among their findings, the researchers noticed that, rather than repel rival males, singing appears to attract other males.
The scientists suggest this may be a potential strategy for male humpbacks to locate a female, since another singing male may often have a female present.
"Song acts as a broadcast signal, and males in the environment around can hear the song as well as the females," Smith said.
"But if another male interacts with a singer, then that singer will typically stop."
Smith says he is confident that male humpback songs are used to woo mates.
Less clear, he says, are the types of information relayed in their songs and how female humpbacks respond when interacting with a singing male.
Smith's research is part of an international project called the Humpback Acoustic Research Collaboration, jointly funded by the United States Office of Naval Research and the Australian Defense Science and Technology Organization.
Smith's academic supervisor, Michael Noad, is a whale expert at the University of Queensland's School of Veterinary Science. Noad has collected thousands of hours of whale songs to better understand them.
"There's a lot of concern about the potential harm to marine mammals from underwater sounds," Noad said.
"We have very little idea of what sounds they do or do not like; [whether] sounds harm them; and if they do, at what level."
In Australia, concerns have been raised that naval exercises using sonar equipment might hurt the whales as they migrate along the coastline.
But Noad says so little research has been done that it is still too early to tell.
(Related story: "Whales Could Be Harmed by Oil-Search Noises, Report Says" [June 2006].)
"We need to learn more about how whales interact with the acoustic environment. Acoustics is their primary sense."
He says learning how whales use and respond to sound needs to be established before researchers can determine whether there are dangerous levels or types of sound.
Once that has been worked out, scientists will then be able to look at whether defense exercises, underwater seismic tests, or even commercial shipping activities are disturbing the humpbacks, Noad says.
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