There are three forms of killer whale: residents who eat fish; transients who eat mammals; and offshores about who little is known. These three types never associate with each other. Scientists have established that residents and transients are genetically distinct and it looks like these two populations of killer whales are on their way to becoming separate species.

Orcas live in all oceans, from the poles to the topics. They have a highly developed social structure and hunt as packs. This, together with their speed and size, means they can hunt even the largestanimals.

Resident orcas are very fussy about the fish they prefer. They take this to an extreme: if their chosen fish species disappear they find it difficult to adapt and choose a new prey. This can even lead to the death of a whale.

The collective name for a group of whales is a pod. Resident killer whales fish in large pods. Transient pods are much smaller, often with only 5 or 6 members, which is more suited for hunting warm-blooded prey. They are also much less vocal: using stealth to surprise their victims.

Resident killer whales have been known to dive to 264 m. Less is known about the diving behaviour of transients but they are thought to stay much shallower.

The killer whale is a toothed whale in the family Delphinidae which comprises the oceanic dolphins, making the killer whale in fact a very large dolphin.

As with other oceanic dolphins, killer whales hear sounds through the lower jaw and other portions of the head, which transmit the sound signals to the middle and inner ears. Killer whale hearing is the one of the most sensitive of any toothed whale.

Female killer whales start having young when they are between 10 and 17 years old. They continue to do so at intervals until they are around 40. Like humans they can live for 90 years or more. Males are shorter lived, estimated at 50-60 years.