Hourglass Dolphin

## Description

The hourglass dolphin (Lagenorhynchus cruciger ) is a small dolphin in the family Delphinidae that inhabits offshore Antarctic and sub-Antarctic waters. It is commonly seen from ships crossing the Drake Passage, but has a circumpolar distribution.

The species was identified as a new species by Jean René Constant Quoy and Joseph Paul Gaimard in 1824 from a drawing made in the South Pacific in 1820. It is the only cetacean to have been widely accepted as a species solely on witness accounts.

## Appearance

The Hourglass dolphin is so called because of the two white colored markings, connected by a thin white band on either flank, reminding an hourglass. This dolphin is also known as a 'sea caw' because of its black-and-white coloration. In Latin, the species is called 'cruciger', meaning 'cross-bearing', since the black and white coloration on the back of the animal appears to be a cross from above. This small and robust dolphin has a stocky and short body. The dolphin has a large dorsal fin. In addition, the tail of the animal often seems to be keeled. Presently, there is no accurate information on the life expectancy of the Hourglass dolphin. However, we can get an idea about the life expectancy of this animal from the lifespan of related species. The dolphin is thought to live as long as other members of its genus. For example, the Atlantic white-sided dolphin lives up to 27 years, while the Pacific white-sided dolphin can live up to 46 years.

## Distribution

The species is found around the higher latitudes of the southern oceans across the Antarctic region. The primary area of its distribution lies around the Antarctic Convergence, between South America and Macquarie Island. The animal is also known to inhabit off the south coast of New Zealand, near the South Shetland Islands as well as around the Tierra del Fuego province. The Hourglass dolphin is a migratory animal, following the cold-water currents: in the winter, the species occurs in northern regions, whereas, during the summer, the dolphin lives in southern waters. This animal favors cold offshore waters, rarely appearing at the seashore.

## Behavior

These dolphins are social animals, usually gathering and travelling in small groups of 7 individuals on average, though there have been also known groups, consisting of up to 100 animals. These highly communicative and playful animals favor riding in the bow waves and wakes of large boats and ships. Noticing a ship in the ocean, they will likely change their course and swim up to the vessel. They are also known to associate with other whales, including the Southern right whale dolphin. As common in toothed whales, Hourglass dolphins navigate and detect prey through echolocation. According to a recently conducted scientific study, the high-pitched clicks that these animals send out, help them locate prey at more than twice the distance of other dolphins. They probably communicate with each other by sight and touch.

## Diet

Hourglass dolphins are carnivores (piscivores and molluscivores).The diet of this animal mainly consists of squid, crustaceans as well as fish.

## Reproduction

At present, there is very scarce information on the breeding system and habits of this dolphin. According to a research, conducted on female Hourglass dolphins, the gestation period in this species lasts for 12 - 13 months, generally yielding a single baby at a time. It is also known that they give birth in August - October. As common in other species of their genus, offspring of this dolphin are thought to be nursed by their mother for 12 - 18, after which they are completely weaned.

## Population

### Population threats

Presently, there are no evident threats to the population of this species. The dolphin does not suffer from commercial hunting. In addition, accidental by-catch has a very small scale, which also does not affect the overall number of their population. The only possible (though unproven) threat is hunting of this species by killer whales.

### Population number

According to IUCN, the Hourglass dolphin is abundant and widespread throughout its range but no overall population estimate is available. However, the population size of this species in the waters south of the Antarctic convergence is estimated to be around 144,300 individuals. Currently Hourglass dolphins are classified as Least Concern (LC) on the IUCN Red List.

## Fun Facts for Kids

These animals can be observed playing around the larger rorqual whales, leaping out of the water and bow-riding waves. This specific habit of Hourglass dolphin helped whalers locate Fin whales.

The Hourglass dolphin is about the size of an average adult male.

These animals favor cold oceanic waters, varying from 32 to 55 degrees Fahrenheit (from 0 to 13 degrees Celsius) in temperature.

Foraging at the water surface, Hourglass dolphins share prey species with seabirds. For this reason, researchers often use seabird flocks to determine locations of hourglass dolphins' feeding and foraging areas.

Hourglass dolphin is an extremely rear species. This animal is the only cetacean, classified as an existing species according exclusively to evidence of eyewitnesses.

Male Hourglass dolphins are called 'bulls', while females of this species are known as 'cows'. Offspring are called 'calves' or 'pups', whereas a group of these dolphins is known as a 'team' or 'school'.

Hourglass dolphins sleep with one of their brain hemispheres in slow-wave sleep in order to be always on the alert. Meanwhile, those living in captivity, where there are no threats, fall asleep completely. Overall, these animals usually sleep for 4 - 5 minutes at a time.

Being marine warm-blooded mammals, Hourglass dolphins breath air, produce maternal milk and give birth rather than laying and incubating eggs.