Dolphin

Dolphins are a type of Cetacean native to Earth, which are known for their intelligence. They are roughly as intelligent as humans, but more playful and with a predatory mindset. The Doctor can speak Dolphin and is on good terms with them.

While sailing in the Indian Ocean, the Doctor spent most of the trip conversing with a school of Dolphins. When Sarah Jane Smith was later pushed overboard, the Doctor was able to get help from a passing family of Orcas. (PDA: Island of Death)