Six of the larger species in the Delphinidae, the Orca and the Pilot, Melon-headed, Pygmy Killer and False Killer Whales, are commonly called whales, rather than dolphins; they are also sometimes collectively known as "blackfish".
Most delphinids primarily eat fish, along with a smaller number of squid and small crustaceans, but some species specialise in eating squid, or, in the case of the Orca, also eat marine mammals. All, however, are purely carnivorous. They typically have between 100 and 200 teeth, although a few species have much less.
Delphinids travel in herds, or 'pods', which may number a thousand individuals in some species. Each herd forages over a range of a few dozen to a few hundred square miles. Some herds have a loose social structure, with individuals frequently joining or leaving, but others seem to be more permanent, perhaps dominated by a male and a 'harem' of females. Individuals communicate by sound, producing low frequency clicks, and also produce high frequency ultrasound whistles of 80-220 kHz, which are primarily used for echolocation. Gestation lasts from ten to twelve months, and results in the birth of a single calf.
Recent molecular analyses indicate that several delphinid genera (especially Stenella and Lagenorhynchus) are not monophyletic as currently recognized. Thus, the coming years will likely see significant taxonomic revisions within the family.