Reproduction

Mating can occur year round but peaks during spring and summer.

Orcas are considered polygamous with both males and females mating with multiple females.

A single calf is born tail first after a 15 to 18 month gestation period. While a single calf is almost always born twins have been recorded on rare occasions.

At birth the dorsal fin and tail fluke are flexible. They harden over the first few days. Their white patches are colored cream, yellowish or tan at birth and turn white over the first year.

Calves feed on milk from the mother which they suckle for 5 to 10 seconds at a time several times each hour. Suckling may occur for up to 2 years. This takes place while underwater. They can swim as soon as they are born.

Sexual maturity appears to be correlated to size. Females reach this between 7 and 16 years old or at lengths of 4.6 to 5.5m (15 to 18ft) long. Males reach this at 13 years old or 5.5m (18ft) long. In captivity they have been recorded to breed at younger ages.

They are one of the only other animals which exhibit menopause. Females do not reproduce after reaching an age between 38 and 46 years old.

Females may produce a calf once every three to ten years.

Behavior

Orcas breathe using the blowhole. This is a circular hole just behind the head which is closed while swimming. It opens to allow air in when they come to the surface.

When swimming they will reach speeds of up to 56km/h (35mph). These high speeds are only reached for short periods before cruising at a slow period. They will ride waves or wakes to reach higher speeds easier.

These highly social animals will live in groups (known as pods) with up to 40 members. These pods includes grandmothers, mothers and their daughters. Hunting techniques are passed down through the generations by these groups.

A number of pods may join together to make a group known as a superpod.

Each pod has a hierarchy with females being dominant.

When the pod travels the young will be in the center with the females while the males are at the edges.

To communicate with one another the orcas with produce a range of whistles, clicks and other calls. They also communicate through body movements including leaping and fin slapping at the surface.

Three ecotypes of orca are recognized These are the residents, transients and offshores. These have different coloration, morphology, behavior and vocalizations. These populations tend not to mix or interbreed even though some have overlapping ranges.

Instead of sleeping like most males dolphins, including orcas, will place one half of their brain in a sleep state at a time.

Predators and Threats

Killer whales have been hunted by humans for a variety of reasons. These include for food and population control along with capture for the captive trade.

Populations are subject to killing as a result of fisherman seeing them as competition. They may also be affected by fisheries which remove their food source. Incidental mortality also occurs from entanglement in fishing lines. Reduction in prey is a larger issue for resident populations which rely on a single food source.

Melting sea ice in the arctic has allowed them to access larger amounts of marine mammals which used to use the sea ice for protection.

Populations have been affected through the accumulation of contaminants within the water. As an apex predator they consume additional poisons within their food. Another threat is oil spills which both affect the whales directly and reduce prey availability.

High levels of tourism in their range affect them through disruption and boat noise which will disrupt echolocation which interrupts their foraging attempts.

Due to the ongoing taxonomic arguments over the status of the orca the IUCN is yet to determine their conservation status and decide if the population is in decline. An estimate of the population is 50,000 individuals.

Despite the name killer whale causing humans to fear orcas no attacks have been recorded in the wild. Unfortunately some attacks have occurred in captive populations.

Recorded causes of mortality for orcas include injuries from prey, stranding while aiming to capture prey and stingray spine injuries while attacking a stingray.

Quick facts

While called a whale the orca is actually the world's largest species of dolphin.

Outside of humans the orca is believed to be the world's most widely distributed mammal.

Orcas are believed to be one of the world's smartest animals rivaling humans and other apes such as chimpanzees.

The name killer whale is believed to have originally been coined as "whale killer" by a fisherman who saw them working together to take down a larger whale.