The iconic humpback whales along Australia’s eastern coast are just not singing as much as they used to.
Two researchers at the University of Queensland (UQ) have found that within an 18-year period, males have shifted from singing to attract a mate, to physically competing with other males.
“In 1997, a singing male whale was almost twice as likely to be seen trying to breed with a female when compared to a non-singing male,” said UQ animal physiologist Associate Professor Rebecca Dunlop.
“But by 2015 it had flipped, with non-singing males almost five times more likely to be recorded trying to breed than singing males.”
Males are thought to sing their soulful songs in part to attract mates, and traditionally those without songs were less likely to find a female.
But what caused the change from singing to fighting? Well for that, you have to go back to our history of whaling.
Before whaling, there was approximately 26,000 eastern Australian humpback whales (Megaptera novaeangliae) living in the Southern Ocean.
But by the 1960s, there were only around 200 left – we had hunted them almost entirely to extinction.
Once whaling was stopped, the numbers rebounded. By 1997 – when this study started, there were 3,700 whales, and by 2015 there was 27,000 whales – back to pre-whaling levels. The researchers also had data from 2004 and 2008 in their dataset, which was recorded near Noosa in Queensland.
This rebound is obviously a fabulous success story. However, with more males, come more problems.
“If competition is fierce, the last thing the male wants to do is advertise that there is a female in the area, because it might attract other males which could out-compete the singer for the female,” Dunlop said.
“By switching to non-singing behaviour, males may be less likely to attract competition and more likely to keep the female.”
This shows a type of ‘social evolution’ occurring in real time, as the population expands.
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“It’s quite a big change in behaviour so humans aren’t the only ones subject to big social changes when it comes to mating rituals,” says Dunlop.
“With humpbacks, physical aggression tends to express itself as ramming, charging, and trying to head slap each other.
“This runs the risk of physical injury, so males must weigh up the costs and benefits of each tactic.”
The research has been published in Communications Biology.