Orcas are the largest of all carnivores on earth
that feeds on a variety of foods, they are found in almost all oceans, from
the tropics to the Arctic and Antarctic where they will go deep into the pack-ice
to hunt seals and penguins. They are commonest in coastal waters and in cool temperate
and sub polar seas.
They have very
sharp stout conical shaped teeth, from 40-48 with
equal numbers in each side of the upper and lower jaws. The teeth can be up to 5cm
(2") long. When a pod of killer whales is feeding, they will co-ordinate their movements
by a continual stream of clicks and calls. Ever ready to spot an opportunity, killer
whales will even follow ice-breakers at the start of the season as they cut paths
through the ice to reach deeper into the ice and perhaps get to seals and penguins
that were beyond their reach.
So adventurous and opportunistic
are killer whales in this respect, that groups of killer whales are thought to have
spent an entire winter living in and around a polynia, an area of open water
kept clear by currents and winds while surrounded by miles of closed ice. These
killers were unable to return to the open ocean as they would have had to have held
their breath under the continuous pack ice for longer than they were able.
In the days of commercial whaling,
while Orcas weren't very much hunted themselves (they were much too small a catch
to waste a harpoon on), they would often follow the whaling boats and rush at the
dead baleen whales that were being flensed or towed alongside the boat ready for
flensing and feed on the carcass. As such, they were much disliked by the whalers
as they competed for the prey that they had just captured. Not for nothing are these
whales called the "wolves of the sea".
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Killer whales swimming in McMurdo Sound Antarctica
- Photo Donald LeRoi, NOAA Southwest Fisheries Science Center, National
Science Foundation
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An interesting aspect of the ecology of Orcas discovered
from studies of populations off Washington state in the USA and up to Alaska is
there are three distinct types that are very similar but differ somewhat in coloration
in morphology (the way they look / proportions etc.) but most of all in their behaviour.
These three types are known as "Residents", "Transients" and "Offshore", they are
discrete populations and little or no mixing between them appears to take place.
Residents - These stay in one location all
through their lives and form very stable communities. They tend to be mainly fish
eaters which they are thought to catch with the help of echolocation. Their dorsal
fins are more rounded at the top compared to the transients that have more pointed
dorsal fins.
Transients - Move around more, they tend to
feed on marine mammals, mainly seals. They form pods with less members than residents
and are not so loyal to a particular pod.
Offshore - The least of all is known about
these (as they live mainly offshore) but they form large pods and move following
the edge of the continental shelves.
Though these groups have only been studied to any
depth in the North Western United States, indications are that the behavioural types
exist elsewhere too.
Orcas feed on a huge range of prey. More or
less, if they find it and catch it, they'll at least have a go at eating it. Different
pods of Orcas seem to have different specialties of diet and will specialize
in a particular type of prey developing and becoming skilled in the ways to capture
that prey. For instance they have been seen:
 | Co-operatively herding fish such as herring
together into tight groups and then slapping them with their tails
to stun them. Otherwise a herring would be a lot of effort and
a small mouth-full for such a large animal. |
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| Surprising young and unwary sea lions off
the coast of Patagonia by chasing after them right into the shallows
and then lunging with a great snap of their powerful jaws. Returning
to sea after a near stranding in these cases takes quite an effort
for the whale. |
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| Breaking through sea ice from below to surprise
seals and penguins, or seeing them on ice-floes and then pushing
upwards on the floe to tip the prey into the water. Alternatively
two whales may rush at an ice floe which is then washed over by
a large wave which dislodge the seal or penguin. |
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| Attacking the great baleen whales such as
blue whale by tearing at and eating the great tongue. A pod
of 40 or so Orcas have been seen engaging in this behaviour attacking
a solitary huge adult blue off the coast of California. |
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Killer whales are often approachable
by boats and are generally inquisitive. They are frequently active at the surface
showing such behaviours as lobtailing, flipper-slapping, spyhopping, wave riding
and breaching.
Rubbing against a hard surface such
as rocks or even other whales is often seen. It is thought to serve as a comfort
movement and helps to remove dead skin. Certain rock rubbing areas may be socially
important.
Like all whales,
sound is very important to killer whales. Researchers
have even identified unique sounds and discrete calls that are distinctive to certain
pods and family groups, to the extent that killer whale dialects can be identified.
Killer
whales or Orcas are probably the best known of the whales, as large carnivores
they have a keen intelligence that enables them to be trained in captivity to do
various tricks for rewards and so have been kept in marine aquariums and "Sea-World"
type exhibits for many years. They are easily identified with their distinctive
black and white patterning.
