The preferred mating strategy of the eastern Australian humpback whale has shifted from singing to fighting in recent years, according to a new study led by Professor Rebecca Dunlop from The University of Queensland.
While analyzing nearly two decades of data, the researchers found that male whales along Australia’s eastern seaboard have given up singing to attract mates. Instead, they are battling it out with other male competitors.
“The eastern Australian humpback whale population was whaled almost to extinction in the 1960s (~200 whales) and has recovered to pre-whaling numbers (>20,000 whales). Using an 18-year dataset, where the population increased from approximately 3,700 to 27,000 whales, we found that as male density increased over time, the use of mating tactics shifted towards more males engaging in non-singing physical competition over singing,” wrote the study authors.
The experts noted that while singing was the more successful mating strategy in earlier post-whaling years, non-singing behavior became the more successful tactic in later years.
“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 Dr. 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.”
“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 the researchers, the transition in mating behavior happened progressively as whale populations recovered from low numbers.
Study co-author Dr. Celine Frere noted that previous work by UQ Professor Michael Noad found that the whale population increased from approximately 3,700 whales to 27,000 between 1997 and 2015.
“We used this rich dataset, collected off Queensland’s Peregian Beach, to explore how this big change in whale social dynamics could lead to changes in their mating behavior,” said Dr. Frere. “We tested the hypothesis that whales may be less likely to use singing as a mating tactic when the population size is larger, to avoid attracting other males to their potential mate.”
“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,” explained Dr. Dunlop. “By switching to non-singing behavior, males may be less likely to attract competition and more likely to keep the female.
“If other males do find them, then they either compete, or leave. 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.”
“It will be fascinating to see how whale mating behavior continues to be shaped in the future.”
The study is published in the journal Communications Biology.
Image Credit: The Cetacean Ecology Group, University of Queensland.
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