When a male humpback whale sings, it hangs its 40-foot-long, 40-ton body upside down in the water and emits some of the most distinctive sounds in the world. According to a 2018 study that analyzed the songs of Australian humpbacks, the whales share an ever-evolving language, like a local dialect, composed of “phrases” joined together to form “themes” that are then arranged to make songs. The squeaks and moans grow more complex as humpbacks add their own embellishments, akin to a folk singer changing a chorus.
While humpback song is believed to serve several purposes, perhaps one of the most important is to attract a mate, but this majestic ritual may be on the decline. A new study of Australian humpbacks has found that the massive mammals now often resort to fighting for love by charging and head-slapping other potential suitors, among other tactics. Such battles tend to happen after a male has cozied up to a female and is swimming alongside her, and others barge in to take his place, as documented in one writer’s account of a whale-on-whale scuffle.
Whaling and Behavior Changes
The upswing in courting violence has a simple explanation, the researchers say: changes in the humpback populations and the legacy of whaling.
Whaling wiped out most humpbacks in the world, leaving only about 200 individuals by the 1960s, and as the population improved, so did the density of males. And when males came in closer contact with each other, they were more likely to stop singing and win mates through non-singing means, including head slaps, the study found. While song attracted females, it also alerted males, who sometimes attempted to assert their dominance.
“Humans aren’t the only ones subject to big social changes when it comes to mating rituals,” says the lead researcher, associate professor Rebecca Dunlop of the University of Queensland, in a press release.
The study presented a unique opportunity to study a population as it recovered from near extinction, using a wealth of data from 1997 to 2015. Researchers relied on a series of hydrophone buoys to record and pinpoint the whale song, and they combined that data with visual observations from atop Emu Mountain, which overlooks the coast of Australia. The site effectively had a sideline view of the whales’ annual migration route to the Antarctic Ocean, where they feed extensively.
In 1997, singing ruled. Widespread fighting came later, during the 2000s, with ramming and charging maneuvers dangerous to both the attacker and the attacked, according to the study.
“Males must weigh up the costs and benefits of each tactic,” says Dunlop in a press release.
Humpback Whale Song Patterns
While males compete aggressively, they also share in a communal song, as Australian populations tend to mimic a unified composition and distinguish themselves by how they diverge from it. This evolution continues until song patterns from outside populations filter in and trigger a “revolution” every few years, a drastic overhaul in which the whales abandon the old for the latest trend.
Read More: Understanding How Whales Communicate
Some humpbacks continue to sing while swimming alongside females, in a kind of serenade, but higher concentrations of males have suppressed this practice, research has found.
“If competition is fierce, the last thing the male wants to do is advertise that there is a female in the area,” Dunlop says in a press release, “because it might attract other males which could out-compete the singer for the female.”