Older male humpback whales are fathering more calves as recovering populations shift toward a more age-balanced structure, according to a study published February 27 in Current Biology by researchers at the University of St. Andrews.
The finding comes from nearly two decades of genetic and behavioral data collected from humpbacks breeding near New Caledonia in the South Pacific — one of the longest-running monitoring efforts of its kind, conducted by the NGO Opération Cétacés.
When populations were still depleted from commercial whaling, breeding groups skewed young. Older males were simply absent in meaningful numbers. As recovery progressed and mature whales returned, they began outcompeting younger rivals for paternity at a measurable rate.
Genetics Reveal What Observation Cannot
Humpbacks have never been directly observed mating in the wild. To establish paternity, the international team led by the Sea Mammal Research Unit used genetic testing from small skin samples. They paired this with an epigenetic molecular clock technique — also applied to skin samples — to estimate each whale’s age without long-term individual tracking.
The combination allowed researchers to connect a calf’s parentage to a specific male and assign that male an approximate age, producing a clearer picture of who was actually reproducing and when.
Senior author Dr. Ellen Garland said: “Mating behavior, and who was successful at mating, changed with these shifts in age structure. As the population recovered, there were more older males than expected singing, escorting females, and successfully fathering calves compared to younger animals.”
Experience as a Competitive Edge
Male humpbacks compete for mates through elaborate songs capable of carrying across large portions of a breeding ground, by closely escorting females, and through direct physical confrontations with rival males. The study suggests these behaviors take years to develop and refine.
Younger males, the researchers argue, may simply lack the vocal sophistication and competitive experience to match their elders. As populations grow further, female selectivity may also increase — potentially deepening the advantage held by males with more developed displays.
The results carry a methodological implication for the broader field. Much of what scientists know about humpback behavior was documented in populations already severely reduced by whaling, meaning researchers were unknowingly studying a distorted baseline. Populations dominated by young whales behave differently from those with a natural age spread, and the behavioral norms recorded during that period may not reflect undisturbed whale society.
The study frames commercial whaling not merely as a historical population collapse but as a disruption whose effects on social structure, competition, and reproductive success have persisted for generations — and are only now beginning to unwind as numbers recover.
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