Dolphins

Dolphins possess large, complex brains relative to their body size — a key indicator of intelligence. They demonstrate self-awareness, passing the mirror test that only a handful of species can achieve. Dolphins use tools: bottlenose dolphins in Shark Bay, Australia, carry sponges on their rostrums to protect themselves while foraging on the seafloor. They learn from each other, passing behaviours culturally through generations. Problem-solving experiments reveal sophisticated reasoning abilities, and dolphins have demonstrated understanding of symbolic language in laboratory settings.

Dolphins navigate and hunt using echolocation — one of the most sophisticated biological sonar systems in nature. They produce high-frequency clicks through specialised structures in their foreheads, then interpret the returning echoes to build a detailed three-dimensional picture of their surroundings. This allows them to detect fish hidden in sand, navigate in complete darkness and identify objects with extraordinary precision. The melon — a fatty organ in the forehead — focuses and directs these sound beams, while the lower jaw conducts returning sounds to the inner ear.

Dolphins are highly social animals that live in groups called pods, ranging from a few individuals to hundreds or even thousands in the case of super-pods. Social bonds are maintained through physical contact, play and complex vocalisations. Each dolphin has a unique signature whistle that functions like a name, allowing individuals to identify each other. Dolphins cooperate in hunting, using coordinated strategies to herd fish. They also show empathy, supporting injured or sick pod members and assisting animals of other species, including humans, in distress.

While many dolphin species are not currently endangered, they face significant threats from human activity. Bycatch — accidental capture in fishing gear — kills hundreds of thousands of dolphins annually. Pollution, particularly plastic and chemical contamination, accumulates in dolphin tissues through the food chain. Underwater noise from shipping, sonar and construction disrupts echolocation and communication. Some species face critical threats: the Māui dolphin of New Zealand numbers fewer than 100 individuals, making it one of the world's most endangered marine mammals. Climate change is altering prey distribution and ocean chemistry, creating additional pressures.