Orcinus orca, which is commonly known as the killer whale, is a marine mammal and the largest species of dolphin. When a calf is born it is seven feet (two m) long and weight a 450 lbs. (200 kg). If a male, or bull, it will grow from 20 to 30 feet (6 to 9 m) long and if female, or cow, 15 to 25 feet (4.5 to 7.5 m) long, and could weight eight tons (seven tonnes). They are colored with black and white patches that are unique from orca to orca. Because of these unique markings marine biologist are able to identify particular orcas and track the lives of these magnificent creatures.
Other then their size difference, males and females are sexed by the shape and size of their dorsal fin. Bulls have a long straight fin, which will sometimes grow to 6 feet in length after maturity and has a tendency to flop over when they breach. Cows have a smaller crescent-shaped fin that, unlike bulls, looks more like the typical dolphin or shark dorsal fin.
Orcas live in groups, or pods, of any number from two to fourty. Although little is known about their social interactions, they do have a "language" which they used to communicate. They seem to be matriarchal. They almost never fight within their pod other than playfully, but will fight with other pods for different reason such as an invasion of territory. Like other dolphins, they use echolocation. Also they enjoy having sexual intercourse. Only dolphins, dogs, chimps and us Homo sapiens are known to have this blessing.
The name orca was given to these animals by the ancient Romans, which means "demon" or "demon from hell." One can take out a great white shark and a pod can take down a large whale. This is where they got their name of asesina ballena, or "whale killer", given to them by Spanish whalers. The term was poorly translated "killer whale" (asesina is assassin or killer, ballena is whale). The term "killer whale" is so common the Spanish now use its translation, ballena asesina.
Contrary to popular belief, sharks are not the kings of sea, orcas are. With no natural predators (other than man) they are at the top of the oceanic food chain.
However, most orcas don't eat whales or other marine mammals. Although orcas are the only Cetacea known to eat other mammals, resident orcas, or those that stay relatively in one area, eat fish, shrimp, turtles, and squid among others but not mammals. Transient orcas, or those that constantly travel, will eat just about anything they can get their pointed three-inch teeth into, including those formerly listed, whales, other dolphins, otters, seals, and others. There has been no known case of an orca attacking or eating a human in the wild. Although in captivity and living in poor conditions orcas have attacked their trainers.
Although I have seem many in the wild, the only orca I have seen in captivity was Bjossa at the Vancouver Aquarium in Vancouver, BC. For you aquarium buffs like me, if you get a chance to go to Vancouver go to the aquarium! It's one of the best in the world. They don't have orcas any more (they don't wish to capture one in the wild and are waiting for an orca to be born in captivity) but their Beluga whales are excellent. Bjossa, being a resident orca and not prone to eating marine mammals, had a bottlenose dolphin for a pin pal, that is they lived in the same pin. They were fun to watch as they played together and with the trainers.
Kingdom: Animalia (animals)
Phylum: Chordata (vertebrates)
Class: Mammalia (mammals)
Order: Cetacea (whales and dolphins)
Suborder: Odontoceti (toothed whales)
Family: Delphinidae (dolphins)
Genus: Orcinus
Species: orca
Sources
http://www.savethewhales.org/killer.html
http://www.pacificwhale.org/childrens/fsorca.html
http://www.whaledom.com/orcadata.shtml
http://www.aquarium.org/keiko/tidbits.htm