Hourglass dolphins are small, robust, dolphins with a unique black and white color pattern. Pigmentation patterns vary greatly amongindividuals, but the sexes are monomorphic.
Hour glass dolphins have highly recurved, falcate dorsal fins with highly keeled tailstocks. The color pigmentation resembles that of an hourglass pattern for which the species gets its common name. It was first described by Qouy and Gaimard in 1824 and was called “cross bearer”.
These dolphins have homodont dentition with 53-69 conical-shaped teeth. The dental formula is 26-34 teeth in the upper jaw with 27-35 teeth in the lower jaw.
The dorsal side is all black with the white flank patches extending up to the keel of the tailstock. The sides are mostly black, marked with two variable white patches. The first (thoracic) patch begins behind the rostrum, extending above the eye and ends mid flank just before the dorsal fin. The rear (flank) patch starts behind the dorsal fin and extends to the tailstock. The two patches may or may not connect below the dorsal fin. The ventrum is mostly white from the rostrum to the tail flukes, which are black. The beak and eyes are outlined with black pigmentation.
The maximum length foris not known, as there are only nine records for this species. The average length of five females was 157.1 cm; 174.5 cm for three males and a third specimen of unknown gender was 155 cm. This measurement was taken from the snout to the tail fluke notch. These records would suggest that males are larger, however not enough data have been recorded to make such an assessment.
The weights of three specimens were recorded. One male weighed 94.0kg and two females weighed 73.5kg and 88.2kg. These data are also consistent with the notion that males of the species are larger than females, but with a sample of so few individuals, no generalizations can be drawn.
These dolphins can easily be distinguished south of the Antarctic convergence. They are the only small dolphin species with a dorsal fin found below this point. Above the convergence they may be confused with dusky dolphins, L. obscurus, and Peale's dolphins, L. australis (Goodall, 1997; Goodall, et al., 1997; Leatherwood and Reeves, 1983)
The mating behavior of these animals is not known.
There are very limited data on reproduction for this species. One female that was 183 cm in length was nearing sexual maturity. Two males that measured 174 cm and 187 cm in length were sexually mature. The age of these animals was not known.
There is some information on reproduction in other memebers of the genus Lagenorhynchus. Study of L. obscurus females killed in Peruvian fisheries indicates that the gestation period is about 12.9 months, and that most births occur late in the Southern Hemisphere winter (August-October). A lactation period of 12 months and an interbirth interval of 28.6 months are also recorded. In L. acutus, nursing last for about 18 months, and young become independant around the age of two years. There is generally only one offspring per pregnancy, but one female of this genus was recorded as having two embryos. Young are 90 to 125 cm in length at birth. (Goodall, et al., 1997; Nowak, 1999)
Females nurse their young, who are able to swim along with their mothers from birth. In other memebers of the genus for which data have been collected, lactation can last from 12-18 months. Other information on parental care is lacking for these animals. (Nowak, 1999)
Hourglass dolphins are social animals and travel in small groups. Social group size varies from one to 100 individuals, with an average group size of seven. It is not known if these groups are made up of related individuals, mixed sexes, or random dolphins. In 223 observed social groups, with a total of 1,634 individuals, only three calves were observed. The low cow-calf ratio may be a result of ship avoidance by cows with calves, or may result from a winter birthing season, when little research is done and few observations are made.
There may be seasonal migrations that follow cold-water currents such as the West Wind Drift. In the summer monthsis more often found in cooler southern waters. The species is found further north during the winter months.
Hourglass dolphins are attracted to large boats and ships and will often change their course of travel to intercept them. They enjoy riding in the bow waves and wakes created by the ships.
In addition to traveling with conspecifics, these dolphins often associate with other species of cetaceans. In one study, hourglass dolphins were encountered 17% of the time traveling with Fin Whales, Balaenoptera physalus; Sei whales, B. borealis; Minke whales, B. acutorostrata; Arnoux’s Beaked Whale, Berardius arnuxii; Southern bottlenose whales, Hyperoodon planifrons; long-finned pilot whales, Globicephala melaena, killer whales and southern right whale dolphins, Lissodelphis peronii. There is one account ofswimming near southern right whales, Eubalaena australis.
The home range of these animals is not known.
There are no recorded data on communication for this species. However, it is likely that like all odontocetes that have been studied, they communicate with high frequency sounds. They are likely to have some tactile and visual communication as well. (Leatherwood and Reeves, 1983)
Hourglass Dolphins feed primarily on fish, squid (Onychoteuthidae and Enoploteuthidae), and crustaceans. Squid beaks from these families were found in the stomach of one specimen, and the remains of Krefftichtys andersonii, a mesopelagic lantern fish were found in another. They are often seen feeding in large congregations near the surface, which attract albatross, petrels and other sea birds. Researchers will often focus in on these large aggregations of birds to locate . (Brownell Jr. and Donahue, 1999; Goodall, 1997)
There is no documentation of predation on these dolphins, however, they are likely preyed upon by killer whales, Orcinus orca. Like many aquatic animals, these dolphins are countershaded. Countershading is widely thought to be an antipredator adaptation, as a light underbelly is difficult to see from below, and a darker dorsal surface is less readily detected from above. (Brownell Jr. and Donahue, 1999)
The niche of hourglass dolphins is not known. They are social animals and will often travel and feed with other whales and dolphins. Based upon their diet, (Goodall, 1997)are most likely secondary or tertiary level consumers. They therefore may play some role in regulating prey populations.
Hourglass dolphins are not commercially harvested, but some are taken annually along with Dusky Dolphins, to be used as crab bait by local fishermen in Chile. Increasing ecotourism in the Antarctic also allows for further observations of this species. (Goodall, 1997; Nowak, 1999)
There is no known negative impact of this species on humans.
Due to its pelagic habits and its distribution in the southern oceans, not much is known about the life history of (Goodall, 1997). To date little research has been done on this species. The measurements used in this account are from a small sample size. Future research will undoubtedly shed some light into the habits and life history of this mysterious dolphin.
Nancy Shefferly (editor), Animal Diversity Web.
Christopher Callahan (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.
the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.
body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.
uses sound to communicate
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
fertilization takes place within the female's body
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
makes seasonal movements between breeding and wintering grounds
eats mollusks, members of Phylum Mollusca
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
generally wanders from place to place, usually within a well-defined range.
An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).
an animal that mainly eats fish
the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.
mainly lives in oceans, seas, or other bodies of salt water.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
young are relatively well-developed when born
Brownell Jr., R., M. Donahue. 1999. Hourglass Dolphin, *Lagenorhynchus cruciger*. Pp. 121-135 in S Ridgeway, H Harrison, eds. Handbook of Marine Mammals: Vol. 6: The Second Book of Dolphins and Porpoises. San Diego: Academic Press.
Goodall, R. 1997. Review of Sightings of the Hourglass Dolphin, *Lagenorhynchus cruciger*, in the South American Sector of the Antarctic and Sub-Antarctic. Report of the International Whaling Commission, 47: 1001-1013.
Goodall, R., A. Baker, P. Best, M. Meyer, N. Miyazaki. 1997. On The Biology of the Hourglass Dolphin, *Lagenorhynchus cruciger* (Quoy and Gaimard, 1824). Report of the International Whaling Commission, 47: 985-999.
Klinowska, M. 1991. Dolphins, Porpoises and Whales of the World. The IUCN Red Data Book. Gland, Switzerland and Cambridge, U.K.: IUCN.
Leatherwood, S., R. Reeves. 1983. The Sierra Club Handbook of Whales and Dolphins. San Francisco, CA: Sierra Club Books.
Nowak, R. 1999. Walker's Mammals of the World, Vol. 2, Sixth edition. Baltimore and London: The Johns Hopkins University Press.