The humpback whales (Megaptera novaeangliae) along Australia’s eastern coast might be giving up singing their signature songs to find a mate. As the competition for females has increased, a new study theorizes that instead of crooning their love songs, the male whales are switching to fighting each other and are possibly staying quiet for their own survival.
Humpback whale songs have been studied for more than half a century, following the development of better underwater microphones in the 1970s that allowed scientists to record them. Only male humpbacks are known to make these elaborate sounds. It is believed that this allows them to attract mates and assert their dominance among other whales.
The population of whales surveyed for the new study, published February 16 in the journal Communications Biology, is a conservation success story. Only about 200 whales were in the area in the 1960s and they have since come back from the brink of extinction. They have been able to survive and thrive primarily due to commercial whaling largely stopping in 1986.
The team used data from 1997 to 2015, when the humpback whale population in eastern Australia exploded from roughly 3,700 whales to 27,000. As the population of whales increased, competition for mates also grew.
“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. But by 2015 it had flipped, with non-singing males almost five times more likely to be recorded trying to breed than singing males,” said study co-author and marine biologist Rebecca Dunlop from The University of Queensland’s School of Biological Sciences, in a statement. “It’s quite a big change in behavior so humans aren’t the only ones subject to big social changes when it comes to mating rituals.”
According to Dunlop, if the competition for a mate is fierce, the last thing a male would want to do is let another male know that a female is in the area by singing. It could attract unwanted competition and be risky.
“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,” said Dunlop.
In an interview with the Associated Press, Simon Ingram, a marine biologist from University of Plymouth said who was not involved with this study said, “Such a big increase in animals over the time they were studying gave them a unique opportunity to get insights about changes in behavior. Clearly singing became incredibly valuable when their numbers were very low.”
The humpbacks in eastern Australia have rebounded close to pre-whaling levels and have even been taken off of the threatened species list. The team can continue to track how the whales’ social behavior changes with their increased numbers.
“Singing was the dominant mating tactic in 1997, but within the space of seven years this has turned around,” said Dunlop. “It will be fascinating to see how whale mating behavior continues to be shaped in the future.”