Whales spend more time 'gesturing' instead of vocalising, to get their point across when the wind whips up the ocean and makes it noisy, say researchers.
Cetacean ecologist Dr Rebecca Dunlop of the University of Queensland in Brisbane and colleagues report their findings today in the Proceedings of the Royal Society B.
"If you imagine you're at a party and you're trying to talk to someone and they can't hear what you say, you start to gesture a bit," says Dunlop.
"Humpbacks are doing something similar."
Humpback whales sing loudly when migrating and breeding, and previous studies have raised concern that noises from human activity might interfere with this.
But, says Dunlop, it's important to consider how whales respond to naturally-occurring noises.
Currents and wind create noise, as do other whales and even shrimp snapping their claws together, she says.
"Underwater can be an extraordinarily noisy place without anthropogenic influences," says Dunlop.
Dunlop and colleagues investigated how humpback whales off the east coast of Australia respond to the noise generated by wind whipping up the waves, which creates similar low frequencies to whale vocalisations.
They recorded the ocean noise using underwater microphones and then compared this to the behaviour of the whales, as recorded by volunteers on land.
The researchers found the more wind noise, the more time whales spent on the surface, breaching and slapping their fins or tails against the water.
Dunlop says the whales are using these physical methods to communicate as an alternative to vocalising, which they carry out underwater.
"It's akin to gesturing," she says.
Dunlop says, the whales can either attract attention through their movements, or through the sound they create with the movements.
While Dunlop's previous research has identified 33 different vocal calls, she says the physical activities at the surface are a "more crude way of communicating".
She says the next step is to use digital recording tags, attached to the whales, to record the animals' movements and underwater sounds.
Dunlop says integrating this with other data on wind noise and surface movement will give a fuller picture of how noise affects whale behaviour.
She also plans to study the impact of human activity.
"I'm going to drive a boat past them and see if they do the same thing," says Dunlop.
She says if whales respond in the same way then it may not be a problem for them.
"We can't get on the bandwagon that [an] increase in noise is always bad," says Dunlop.
The research was funded by the US Office of Naval Research, the Australian Defence Science and Technology Organisation and the Australian Marine Mammal Centre.
Effect of seismic blasts
Dunlop and colleagues have recently been granted around $10 million from a conglomeration of oil companies for a four-year study of the impact of seismic exploration on whales.
Associate Professor Rob McCauley from Curtin University's Centre for Marine Science and Technology in Perth, who will be involved in the seismic noise study, says human activity is a particular worry in whale breeding areas.
"The breeding areas for a lot of the whales that are vocal do tend to be the quiet areas," says McCauley, who is currently advising the US Navy on where it should not use its sonar.
"The whales sing to each other - it's a courtship thing - it's part of the breeding cycle. So you wouldn't want to add a lot of man-made noise in those environments and force them into a different type of behaviour."
McCauley says noise can also have a cumulative effect and it is important that whale behaviour is not constantly being altered.