As Humpback Whales Rebound, Older Males Take Over the Mating and Singing Game

Older male whales are getting most of the mates and leaving younger rivals behind.

As humpback whale numbers climb back after decades of large-scale hunting, scientists are spotting strange things. A new study reveals that older males are now more likely to father calves, while younger ones are being edged out. 

This pattern has grown stronger over time, hinting that the whaling (whale hunting) didn’t just reduce whale numbers—it changed the balance of age and experience, and that is still shaping who succeeds in reproduction today.

“We are beginning to understand how far-reaching the consequences of whaling truly are. The impacts extend beyond population size, they shape behaviour, competition, and reproduction,” Franca Eichenberger, lead study author and a whale researcher at the University of St Andrews in Scotland, said.

A detective story written in DNA

In decades of studying whales, no one has ever witnessed humpback whales mating in the wild. This left a major gap in understanding how reproduction really works in these giants.

To tackle this, researchers from the University of St Andrews and their collaborators relied on long-term fieldwork in New Caledonia, tracking whales between 2000 and 2018. 

“We assessed age-dependent population dynamics, reproductive tactics, and reproductive success of 485 male humpback whales (Megaptera novaeangliae) from a recovering breeding ground in New Caledonia,” the study authors note.

They collected small skin samples from hundreds of males using remote biopsy tools—a harmless procedure but incredibly informative. These samples became the key to solving two problems at once. First, genetic comparisons between males and known mother–calf pairs allowed the team to identify 56 confirmed fathers. 

Second, they used an epigenetic clock—a method that reads age-related chemical changes in DNA—to estimate how old each whale was. This approach bypassed a lot of guesswork, since humpback whales don’t have clear physical markers of age.

By combining identity and age, the researchers could finally map out who was reproducing. Then came the surprises.

“You are able to assess the age structure of a population by looking at all the individuals, not just the ones you are able to track over time,” Angela Sremba, a researcher at the Marine Mammal Institute at Oregon State University, told The Washington Post. She wasn’t involved in the study.

A comeback that raised the stakes

The long-term data revealed a shift that only became visible as the population recovered. In the early 2000s, the whale population was still sparse after decades of intense whaling. Most males in the breeding grounds were relatively young, simply because older generations had been heavily depleted. 

×

Get smarter every day...

Stay ahead with ZME Science and subscribe.

Daily Newsletter
The science you need to know, every weekday.

Weekly Newsletter
A week in science, all in one place. Sends every Sunday.
No spam, ever. Unsubscribe anytime. Review our Privacy Policy.

Thank you! One more thing...

Please check your inbox and confirm your subscription.

In that environment, younger males had a fair chance at reproduction. However, as numbers grew over the following decade, the age structure balanced out. Older males became more common—and with them came a noticeable change in mating success. 

Males aged 16 and above were increasingly likely to father calves, and this advantage strengthened as the population expanded. Older males were also more frequently seen engaging in key behaviors linked to reproduction. 

For instance, they produced long, powerful songs that travel across breeding grounds, stayed close to females, and competed more actively with rivals. In contrast, younger males were less successful in securing these opportunities.

“As the population recovered, there were more older males than expected singing, escorting females, and successfully fathering calves compared to younger animals,” Ellen Garland, one of the study authors and an expert on sea mammals, added.

Over time, males may improve their songs, build stamina, and learn how to navigate competition. At the same time, females in a larger population may have more choices, allowing them to favor males with stronger displays or better traits.

Why do these findings matter?

When a smaller number of older males dominate reproduction, fewer individuals pass on their genes, which could reduce genetic diversity over time. Yet earlier in the recovery phase, when younger males reproduced more evenly, that may have helped the population rebound more effectively.

However, researchers don’t yet know exactly which traits give older males their edge, or how these patterns might evolve as populations continue to stabilize. There’s also a broader limitation—modern science is studying whales that have already been altered by human activity, meaning the true baseline of their natural behavior remains unknown.

RelatedPosts

Highly venomous sea snakes may be attacking scuba divers as a mating behavior
Ancient 36-million-year-old fossil helps track down how baleen whales lost their teeth
We pick our mates by their genome — even if we aren’t aware of it
Fungus turns frogs into sex zombies, but then kills off whole species

The next important step is continued observation. By tracking these whales over longer periods and using advanced genetic tools, scientists hope to understand whether this age advantage persists or shifts again. 

“Virtually all populations of whales have changed due to whaling; our work shows that they continue to change as they recover. This is why the continued long-term monitoring of previously exploited whale populations is so important,” Eichenberger said.

The study is published in the journal Current Biology.