University of Queensland researchers said Wednesday that they believe the male's songs are part of an elaborate courtship ritual between humpback whales as they appear to be directed more towards females than to warn off rival males.

"The male singers are spending a lot more time singing with the females," said researcher Joshua Smith.

While he cannot say the songs attract the females, they do facilitate sex.

"Certainly there's evidence for courtship. It seems to certainly be a courtship display that facilitates mating interactions with females," he said.

Smith said the characteristics of the song were possibly being used by the females to assess the singing males.

"The way they structure the songs, perhaps using particular elements like higher or lower frequencies and how well they do that could reflect attributes of that male such as his fitness, maybe his age," he said.

He said the songs, made up of chirps, moans and barks, were repetitive but structured and could be detected as far as 20 kilometres (12 miles) away.

"The singing can last as long as 10, 15, 20 minutes to as long as 23 hours -- on average we are looking at three hours," Smith said.

Smith has worked with a team of scientists and volunteers to track whales off the eastern Australian coast for three years as the sea-dwellers migrate south from their breeding areas near the Great Barrier Reef.

"We've still got such a long way to understanding the humpback whales and the social systems involved," he said.

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