His killer whale observation, published in 1995, and the Argentinian report were among the first in a rapidly growing body of research that supports the existence of cultural traditions among whales and dolphins. The Dalhousie biologists portray the four best-studied cetacean species—the bottlenose dolphin, the killer whale, the sperm whale, and the humpback whale—as generators of group-based, cultural systems of communication, feeding, mating, and raising their young. Killer and sperm whales live in groups headed by related females who possess distinctive cultural traits, Whitehead argues.