The spinner dolphin (Stenella longirostris) is renowned for its spectacular acrobatic displays, a behavior that gives the species its common name. The spin involves the dolphin leaping high out of the water and rotating rapidly on its long axis, often completing multiple revolutions before splashing back down. While this dramatic, high-energy behavior is a source of fascination, the exact purpose remains a subject of scientific inquiry, with researchers proposing several hypotheses that may all contribute to the overall function.
Spin as a Communication Signal
The most widely supported hypothesis suggests that the spin primarily functions as a sophisticated form of social signaling within the dolphin group. The true communicative event is not the aerial rotation itself but the forceful re-entry into the water, which often culminates in a loud side-slap. This action generates a significant noise and a large splash that travels considerable distances both above and below the surface. This visual and auditory effect serves a purpose in group coordination, acting as a long-range alert system that can be detected by other dolphins in the area. It allows dolphins to signal a change in activity, such as moving from daytime resting to nocturnal offshore feeding grounds.
The Function of Parasite Removal
Another compelling explanation for the spinning leap is that it helps the dolphin maintain its physical health by dislodging external organisms. The body is occasionally afflicted by ectoparasites, such as remoras, which attach themselves to the skin and increase drag, requiring the dolphin to expend more energy to swim. The combination of the rapid rotation in the air and the subsequent jarring impact of the water re-entry may be sufficient to physically detach these hitchhikers. Computational models support this theory, demonstrating that the force generated can create enough stress on the remora’s suction disk to weaken its hold. However, some research suggests this is not the behavior’s primary function, as dolphins perform the spin even when no remoras are present.
Play Orientation and Group Cohesion
The spinning behavior may also be an expression of simple exuberance, serving as a form of play, particularly for younger dolphins with excess energy. The acrobatic nature of the spin fits well within the spectrum of observed playful behaviors, suggesting it acts as a behavioral discharge, releasing pent-up energy after long periods of resting. The momentary elevation above the water’s surface also provides the dolphin with an opportunity for visual orientation. By leaping high, an individual can quickly survey the immediate environment, checking for predators or observing the location of the larger group. This brief visual assessment contributes to group cohesion, allowing the dolphin to re-establish its bearings and confirm the school is moving as a unified unit.