The idea of a dolphin as a friendly, smiling resident of the ocean is deeply ingrained in human culture. These highly intelligent marine mammals are often featured in media as playful and helpful, reinforcing a perception of innate goodness. However, scientific evidence reveals a far more complicated picture of their social lives. Dolphin society includes behaviors that, if observed in humans, would be considered highly aggressive, manipulative, and violent. This understanding prompts a direct examination of the question: is the dolphin capable of behavior that warrants the label of a bully?
The Complexities of Dolphin Society
Dolphins, particularly the common bottlenose dolphin, live in a dynamic social structure known as a fission-fusion society. Group membership is highly fluid, with individuals frequently joining and leaving small subgroups over hours or days. This constant shifting demands a high degree of social intelligence and long-term memory to manage relationships and alliances.
The maintenance of these complex networks relies on established dominance hierarchies, which are reinforced through physical displays.
Aggressive interactions are a normal part of maintaining social order and establishing rank. Dolphins use a behavior called “raking,” where they scrape their teeth across the skin of a rival, leaving superficial, parallel white scars. These actions, along with head-butting and jaw-popping, communicate status without inflicting serious physical damage. This sophisticated social environment, characterized by intense cooperation, creates conditions for intense competition.
Documented Acts of Aggression and Harassment
The darker side of dolphin behavior is illustrated by numerous documented acts of severe aggression, both within their own species and against others. One shocking behavior is infanticide, the killing of young calves, recorded across multiple dolphin species. The attacks are typically carried out by adult males using coordinated ramming and tossing to inflict fatal blunt-force trauma. Post-mortem examinations on young stranded calves have confirmed the cause of death as violence from conspecifics.
Dolphins also exhibit aggressive behavior toward smaller cetaceans, notably the harbor porpoise, in incidents sometimes termed “porpicide.” Bottlenose dolphins have been observed chasing, ramming, and violently tossing porpoises, sometimes killing them without consuming the carcass. The injuries inflicted are consistent with those seen on dolphin calves attacked by adult males, suggesting a link between the two behaviors. This non-predatory aggression, involving the sustained harassment and killing of a smaller, non-threatening animal, is a primary reason the term “bully” has been applied to the species.
The Ecological and Reproductive Drivers
The motivation behind these aggressive acts is rooted in evolutionary and reproductive imperatives, not random malice. The infanticide committed by male dolphins is directly linked to the sexual selection hypothesis. A female dolphin will not enter estrus while she is nursing a calf. By killing an unrelated calf, a male accelerates the mother’s return to a breeding state, increasing his mating opportunities.
Reproductive competition drives the formation of powerful male alliances, which cooperate to gain and maintain access to females. These alliances engage in herding, where a group of two or three males isolate a single female and aggressively prevent her from leaving or mating with other males. This sexual coercion can last for weeks and is a violent method of ensuring paternity. The aggressive encounters with porpoises may be an outlet for this high-testosterone, alliance-driven aggression, perhaps serving as practice for infanticidal attacks or misdirected aggression when conspecific targets are unavailable.
Applying the Term “Bully” to Animal Behavior
The question of whether dolphins are truly “bullies” requires separating human morality from biological function. The human definition of bullying implies malicious intent and unnecessary cruelty, often for psychological gain. In contrast, dolphin aggression, however brutal, is functional behavior driven by competition for resources and reproductive success.
These actions are successful, albeit violent, survival strategies selected for through evolution. While the documented acts of infanticide and harassment are disturbing to human observers, they are part of a complex, high-stakes social landscape. Therefore, dolphins exhibit behaviors that match the description of bullying—repeated, non-predatory aggression toward a weaker individual—but the underlying reason is an evolutionary drive, not a moral failure.