Female dolphins remember which males are aggressive and use that information to choose mating partners, new research suggests. Scientists have discovered that bottlenose dolphins can identify individual males by their unique calls and keep track of their past behaviour, avoiding the most coercive ones during mating season.
Complex Dolphin Societies
Prof Stephanie King, an expert in animal behaviour at the University of Bristol, explained that dolphin society is intricate, with males and females often knowing each other for decades. Relationships can be positive, with males performing displays or engaging in affiliative behaviours like touching. However, during mating season, males often collaborate in pairs, trios, or larger alliances to gain access to females through aggressive herding, known as consortships, which can last from hours to weeks.
King noted that male dolphins "work together to keep her with them for as long as possible," sometimes being "quite coercive." They restrict the female's movements and keep her in areas they prefer, near other males that can help defend her from rivals.
Research Methods
The study, published in the Proceedings of the National Academy of Sciences, involved a population of Indo-Pacific bottlenose dolphins in Shark Bay, Western Australia, studied for over 40 years. Researchers collected 34 signature whistles from male dolphins and played them underwater to 17 female dolphins, using drones to observe responses.
Reproductively available females showed significantly stronger avoidance responses to whistles of males with higher rates of coercion, indicating awareness of their past behaviour. King explained: "It's like 'I keep track of which males might be more likely to herd me. And if I don't want to be herded, I'm going to show an avoidance response.'" Unavailable females—older or with calves—did not show the same level of response.
Expert Commentary
Dr Mike Bossley, an Australian cetacean researcher not involved in the study, called it "an imaginative and valuable field study confirming the complexity of dolphin societies." He added that it shows female dolphins can identify the behavioural characteristics of males, essentially knowing each male's personality to help choose who fathers their calf.
