Whales and Dolphins Uniting for Survival, Bounty, or Companionship?

Whales, dolphins, and porpoises (also called cetaceans) exhibit remarkable social behaviors. Sometimes, some species can form large pods that may span for miles and consist of thousands of individuals. One intriguing aspect of cetaceans’ social dynamics is the ability to establish connections beyond their species. These relationships transcend traditional species boundaries, with two or more distinct species choosing to associate for reasons extending beyond mere resource accumulation.

Scientists believe these interspecies associations might serve diverse purposes, typically falling into one of four categories: predator deterrence, predator avoidance, foraging beneficence, and socialization. Each category offers unique insights into the complex world of heterospecific relationships among cetaceans. This post aims to unravel the mysteries behind why these different cetacean species choose to unite, what benefits they could derive from these connections, and even questions whether they can communicate with one another.

Survival in numbers: predator deterrence

Predator deterrence is one of the main driving factors for smaller-sized cetacean species choosing to associate. Predator deterrence is a strategy employed by animals to discourage potential predators from targeting them. Prey species may achieve this through various means, such as forming large groups or displaying behaviors that signal difficulty or danger for a predator attempting to prey on an individual within the group.

This type of association can occur in many different species throughout the world. One example of this kind of heterospecific relationship in cetaceans is the Pacific white-sided dolphins and the Northern right whale dolphins. Some aggregations of these species can be thousands strong when encountered in Monterey Bay. There, scientists believe these large groups deter predators from trying to attack.

Teaming up against predators through good timing

Keeping watch for predators (called predator avoidance) is crucial for survival, and some dolphin species have figured out a clever way to do it – by teaming up and taking shifts. Whales and dolphins do not sleep like humans, they rest in sleep cycles with only half of their brains asleep at a time.

In the tropical Pacific Ocean, pantropical spotted dolphins and Eastern spinner dolphins face threats in their open-ocean habitat due to the lack of cover from predators. To mitigate this risk, they’ve developed a remarkable strategy: they coordinate their feeding times. Spinner dolphins are nocturnal, so keep watch at night. Spotted dolphins take over during the day, while spinner dolphins seek refuge among the spotted dolphins for their rest periods. In the end, both species benefit from each other’s vigilance.

Alliances for a bountiful feast

Foraging beneficence happens when different species join forces to maximize their food sources. Much like the collaboration between the blue wildebeest, plains zebra, and Thomson’s gazelles in the Maasai Mara, cetaceans also engage in these cooperative endeavors to make the most of a food source.

The North Atlantic Ocean brings us a great example of foraging beneficence: the dynamic partnership between humpback whales and killer whales. In a spectacular display of teamwork, both species converge to feast on large shoals of herring. By pooling their efforts, these marine giants ensure the most substantial food intake possible.

Teaming up to socialize?

The peak of complexity in heterospecific relationships occurs when the primary goal is socialization. Defining socialization is not a straightforward task; it involves any interaction between different species that defies easy categorization. Sometimes, these encounters can take a negative turn: think of the aggression between common bottlenose dolphins and Atlantic spotted dolphins. But other examples prove to be complex and fascinating.

The spectrum of socialization extends to special examples of altruism and care, illustrated by a documented case of an Indo-Pacific bottlenose dolphin nursing an Australian humpback dolphin calf, an intriguing behavior called alloparenting. Another example is the “altruistic” characteristics of humpback whales. Scientists reported cases where they “protect” other marine mammal species from killer whale predation (we kept quotation marks to avoid falling into an anthropomorphism trap).

While the precise mechanisms driving these interspecies interactions remain poorly understood, some cases suggest the potential for interspecific communication among cetaceans. A noteworthy example involves a lonely short-beaked common dolphin producing clicks similar to harbor porpoises. We wrote a story about it, find it here. While these social interactions and potential forms of communication remain mysterious, we look forward to future research shedding light on these complex aspects of cetacean behavior!

The recap of our post in infographic format — Credit: A. Remili / Illustrations: A. Remili & A. Smith / Footage in Norway: K. Balotay

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Sources and further reading

• Norris, K. S., & Dohl, T. P. (1980). Behavior of the Hawaiian spinner dolphin, Stenella longirostris. Fishery bulletin, 77(4), 821-849.
• Stensland, E. V. A., Angerbjörn, A., & Berggren, P. E. R. (2003). Mixed species groups in mammals. Mammal Review, 33(3‐4), 205-223.
• Pitman, Robert L., et al. “Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?.” Marine Mammal Science 33.1 (2017): 7-58.
• Conry, D. S., De Bruyn, P. J., Pistorius, P., Cockcroft, V. G., & Penry, G. S. (2022). Alloparental care of a bottlenose and common dolphin calf by a female Indian Ocean humpback dolphin along the Garden Route, South Africa.

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