London, Aug 3 - Hydrophones have revealed that bowhead whales can sing in different voices to attract a mate and thereby ensure the species' survival.

This is probably because global warming has opened up the Northwest Passage in 125,000 years, enabling the 100 tonne bowhead whales of the northern Pacific to reach Disko Bay in Greenland to mate with other whales.

It wasn't that many years ago that the bowhead whale was written off as extinct in the waters off Greenland where University of Copenhagen (U-C) has its Arctic field station and is conducting a study on these love songs.

'Whale song is not a new phenomenon. But the special thing about the bowhead whale's song is that they sometimes sing with 'more than one voice',' said Outi Maria Tervo, scientific leader of the project at the U-C.

'They produce two different songs or sounds, which are then mixed together. This has not been seen in other baleen whales. It turns out that bowhead whales have a new repertoire each year - presumably as part of the eternal struggle to obtain a mate,' said Tervo.

Tervo will be presenting her studies on these love songs of bowhead whales at an international conference on marine mammals later this year in Canada.