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The dusky dolphin is small to medium in length compared with other species in the family. There is significant variation in size among the different population areas. The largest dusky dolphins have been encountered off the coast of Peru, where they are up to 210&nbsp;cm (6&nbsp;feet) in length and 100&nbsp;kg (210 pounds) in mass. The size for dusky dolphins in New Zealand have been recorded to be a length range of 167–178&nbsp;cm and a weight range of 69–78&nbsp;kg for females and a length range of 165–175&nbsp;cm and a weigh range of 70–85&nbsp;kg for males.<ref name= "Cipriano 1992">{{cite book |last=Cipriano |first=F. W. |year=1992 |title=Behavior and occurrence patterns, feeding ecology, and life history of dusky dolphins (''Lagenorhynchus obscurus'') off Kaikoura, New Zealand |type=Phd. Thesis |publisher=University of Arizona}}</ref> There is almost no [[sexual dimorphism]] in this species, although males have more curved dorsal fins with broader bases and greater surface areas.<ref name= "Perrin"/> The back of the dolphin is dark grey or black, and the [[dorsal fin]] is distinctively two-toned—the leading edge matches the back in color, but the trailing edge is a much lighter greyish white. Dusky dolphins have a long, light grey patch on their foreside leading to a short, dark grey beak. The throat and belly are white,<ref>Webber, M.C. 1987. "A comparison of dusky and Pacific white-sided dolphins (genus . Lagenorhynchus): morphology and distribution". M.S. Thesis, San Francisco State Univeristy, San Franciso CA. 102 pp.</ref> and the beak and lower jaw are dark grey. There are two blazes of white color running back on the body from the dorsal fin to the tail. Right between the white areas remains a characteristic thorn-shaped patch of dark colour, by which the species can easily be recognized. Aside from that, dusky dolphins may be confused with other members of their genus when observed at sea.

It can be distinguished from the [[common dolphin]]s, which have a more prominent and longer beak and yellow flank markings.<ref name=Menkhorst>{{cite book|last=Menkhorst|first=Peter|title=A Field Guide to Mammals of Australia|publisher=Oxford University Press|location=South Melbourne, Victoria|date=2001|pages=226-27|isbn=0-19-550870-X}}</ref> The skull of a dusky dolphin has a longer and narrower rostrum than that of a [[hourglass dolphin]] or [[Peale's dolphin]] of similar age and size.<ref>Fraser, F. C. 1966: Comments on the Delphinoidea. In: "Whales, Dolphins and. Porpoises," K. S, Norris (Ed.), pp. 7-37, University of California Press. ISBN 0520032837

</ref>

 

[[File:Dusky dolphin Kaikoura.jpg|thumb|250px|left|Dusky dolphins off New Zealand]]

The dusky dolphin has a discontinuous semi-[[wikt:circumpolar|circumpolar]] range. The dolphins can be found off the coasts of South America, southwestern Africa, southern Australia and Tasmania, New Zealand and some oceanic islands. Off South America, dusky dolphins range from southern Peru to [[Cape Horn]] in the west and from southern [[Patagonia]] to around 36º S in the east.<ref name= "Perrin">Waerebeek, K. V., Wursi, B. "Dusky Dolphin ''Lagenorhynchus obscurus''" pp. 335–37 of ''Encyclopedia of Marine Mammals'' (edited by Perrin, W. F., Wursig, B and J. G.M. Thewissen), Academic Press; 2nd edition, (2008) ISBN 012373553X

Dusky dolphins are found throughout New Zealand waters. The center of their abundance is from [[East Cape]] and [[Cape Palliser]] on the [[North Island]] to [[Timaru]] and Oamaru on the [[South Island]].<ref name= "Gaskin 1972">Gaskin, D E. (1972) [http://www.andrewisles.com/all-stock/publication/whales-dolphins-and-seals-with-special-reference-to-the-new-zealand-region "Whales dolphins and seals with special reference to the New Zealand region"]. Heinemann Educational Books Ltd.</ref> They are especially common in the cold waters of the Southland and Canterbury currents.<ref name= "Gaskin 1972"/> In Africa, the dusky dolphin ranges from Lobito Bay, Angola in the north to [[False Bay]], South Africa in the south.<ref name= "Perrin"/> Within Australian waters, Dusky dolphins have been recorded in colder waters off [[Kangaroo Island]], eastern Tasmania and [[Bass Strait]],<ref name=Menkhorst/> although they are uncommon and those that are sighted there are possibly transients from New Zealand.<ref>{{cite journal |last1=Gill |first1=Peter C. |last2=Ross |first2=Graham J. B. |last3=Dawbin |first3=William H. |last4=Wapstra |first4=Hans |title=CONFIRMED SIGHTINGS OF DUSKY DOLPHINS (''LAGENORHYNCHUS OBSCURUS'') IN SOUTHERN AUSTRALIAN WATERS |journal=Marine Mammal Science |volume=16 |pages=452–59 |year=2000 |doi=10.1111/j.1748-7692.2000.tb00937.x}}</ref> Dusky dolphins are also found around Campbell, Auckland and Chatham in the western South Pacific, [[Tristan da Cunha]] in the South Atlantic and [[Île Amsterdam]] and [[Île Saint-Paul]] in the southern Indian Ocean.<ref name= "Audubon">{{RefAudubonMarineMammals}}</ref>

 

[[File:Dusky dolphin pod.jpg|thumb|250px|right|A pod of dusky dolphins]]

Dusky dolphins prefer cool, upwelling waters as well as cold currents. They largely live in inshore waters but can be found in the outer continental shelf and offshore islands.<ref name= "Gaskin 1972"/> Dusky dolphins can move over great distances (around 780&nbsp;km) but have no well defined seasonal migrations.<ref name= "Perrin"/> However, dolphins off Argentina and New Zealand make inshore and offshore seasonal and diurnal movements.<ref name= "Perrin"/> In Argentina, dusky dolphins associate closely with [[southern right whale]]s and [[South American sea lion]]s.<ref name= "behavior"/> They have been found close to, but have apparently not interacted with, [[bottlenose dolphin]]s and may feed in the same areas as [[Risso's dolphin]]s.<ref name= "behavior"/> They also associate with various seabirds like [[kelp gull]]s, [[cormorant]]s, [[tern]]s, [[shearwater]]s, [[petrel]]s and [[albatross]]es.<ref name= "behavior"/> In New Zealand, dusky dolphins mingle with [[common dolphins]].<ref name= "Cipriano 1992"/> Dusky dolphins have also been observed with [[southern right whale dolphin]]s and [[pilot whale]]s off southwestern Africa.<ref>Cruickshank, R.A. & S.G. Brown (1981) "Recent observations and some historical records of southern right-whale dolphins ''Lissodelphis peronii''", ''South African Fishery Bulletin'', 15(1):109–21. [http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=196180&q=Recent+observations+and+some+historical+records+of+southern+right-whale+dolphins&uid=789414412&setcookie=yes Abstract]</ref>

 

In general three different types of sounds are produced by dolphins (and other [[toothed whales]]). These are click trains, which are a series of individual clicks, usually broadband signals with a rapid rise time,<ref>Caldwell, M.C; Caldwell D.K (1971) "Underwater pulsed sounds produced by captive spotted dolphins, Stenella plagiodon", ''Cetology'' 1:1–7.</ref> burst pulses, which are individual clicks whose repetition is so high that they are heard by humans only as a buzzing sound<ref name = "Yin 1999"/> and whistles, which are pure-tone, narrow-banded frequency modulated signals which vary in frequency with time. Dusky dolphins have been recorded to make all three sounds but most commonly make burst pulses.<ref name = "Yin 1999">SE Yin (1999) [http://reference.kfupm.edu.sa/content/m/o/movement_patterns__behaviors__and_whistl_76082.pdf "Movement patterns, behaviors, and whistle sounds of dolphin groups off Kaikoura, New Zealand"], A Thesis, Texas A&M University, College Station, TX.</ref> Whistling is more common when dusky dolphins mingled with other dolphin species like [[common dolphin]]s.<ref name= "acoustics">Au, W.W.L.; Lammer, M.O; Yin, S."Acoustics of Dusky Dolphin (''Lagenorhynchus obscurus'')". Pp. 75–98 in: Würsig, B., and Würsig, M., editors. ''The Dusky Dolphin: Master Acrobat off Different Shores''. Academic Press. (2010) ISBN 0123737230</ref>{{rp|79}} Dusky dolphins project broadband short-duration [[Animal echolocation|echolocation]] signals similar to that of other whistle-producing toothed whales.<ref name= "acoustics"/>{{rp|95}} Most of the species' echolocation signals have bi-modal frequency spectra with a low-frequency peak between 40 and 50&nbsp;kHz and a high-frequency peak between 80 and 110&nbsp;kHz.<ref name= "echolocation">{{cite journal |last1=Au |first1=WW |last2=Würsig |first2=B |title=Echolocation signals of dusky dolphins (''Lagenorhynchus obscurus'') in Kaikoura, New Zealand. |journal=The Journal of the Acoustical Society of America |volume=115 |issue=5 Pt 1 |pages=2307–13 |year=2004 |pmid=15139642}}</ref> The levels of the echolocation signals are about 9–12&nbsp;[[Decibel|dB]] lower than for the larger [[white-beaked dolphin]] which belongs to the same genus but is over twice as heavy as the dusky dolphins.<ref name= "echolocation"/>

 

[[File:Dusky dolphins.jpg|thumb|250px|left|A dusky dolphin pair]]

Dusky dolphins prey consume a variety of fish and squid species. Common fish species eaten include [[anchovies]], [[lantern fish]], [[pilchard]]s, [[sculpin]]s, [[hake]]s, [[horse mackerel]], [[Blue grenadier|hoki]] and [[Red codling|red cod]].<ref name= "Perrin"/> They are generally coordinate hunters. These dolphins have very flexible foraging strategies that can change depending on the environment.<ref name= "Benoit 2004">Benoit-Bird, K.J., Würsig, B., and McFadden, C.J. 2004. "[http://people.oregonstate.edu/~benoitbk/reprints/dusky%20foraging%20mms.pdf Dusky dolphin (''Lagenorhynchus obscurus'') foraging in two different habitats: active acoustic detection of dolphins and their prey]." ''Marine Mammal Science'' '''20'''(2): 215–31.</ref> In certain parts of New Zealand, were deep oceanic waters meet the shore, dusky dolphins forage in [[deep scattering layer]]s at night.<ref name= "Benoit 2004"/> They arrive at the hunting site individually but form groups when in the layer.<ref name= "Benoit 2004"/> The dolphins use their echolocation to detect and isolate an individual prey.<ref name="echolocation" /> Groups of foraging dolphins tend to increase when the layer is near the surface and decrease when it descends.<ref name= "Benoit 2004"/>

When hunting in shallower waters in New Zealand and Argentina, dusky dolphins tend to forage during the day. The dolphins chase schools of fish or squid and herd them into stationary balls.<ref name= "McFadden 2003">McFadden, C. J. (2003). "Behavioral flexibility of feeding dusky dolphins (Lagenorhynchus obscurus) in Admiralty Bay, New Zealand." M.Sc. thesis, Texas A&M University, College Station , TX.</ref> They may control the school by using light reflected from their white bellies.<ref>{{cite book |last1=Würsig |first1=B. |first2=T. R. |last2=Kieckhefer |first3=T. A. |last3=Jefferson |year=1990 |chapter=Visual displays for communication in cetaceans |pages=545–59 |title=Sensory Abilities of Cetaceans |editor1-first=J. |editor1-last=Thomas |editor2-first=R. |editor2-last=Kastelein |publisher=Plenum Press |isbn=0306436957}}</ref> Dolphins herd prey against the surface but also horizontally against the shore, a point of land or the hull of a boat.<ref name= "McFadden 2003"/> During these times, it is believed that dusky dolphins increase prey availability for other predators including other dolphins, [[seabird]]s, [[shark]]s and [[pinniped]]s. In Argentina, dusky dolphins may use bird aggregations to coordinate foraging efforts.<ref name= "behavior"/> On the other hand, pinnipeds and sharks [[Kleptoparasitism|take advantage]] of the dolphin hunts which leave almost no advantage to the dolphins.<ref name = "Markowitz 2004">Markowitz, T.M. (2004). "Social organization of the New Zealand dusky dolphin". Ph.D . dissertation, Texas A&M University, College Station.</ref> Dusky dolphins are themselves preyed on by [[killer whale]]s and large sharks. Dolphins avoid killer whales by swimming into shallower water.<ref name= "behavior">Würsig, B.; Würsig, M. (1980) [http://fishbull.noaa.gov/77-4/wursig.pdf "Behavior and ecology of the dusky dolphin, Lagenorhynchus obscurus, in the South Atlantic"]. ''Fishery Bulletin'' 77: 871–90.</ref> Dusky dolphins are also susceptible to [[parasitism]] by certain [[nematode]], [[cestode]] and [[trematode]] species, mostly ''Nasitrema'' sp., ''[[Anisakis]]'' sp., ''Phyllobothrium delphini'', ''Braunina cordiformis'' and ''Pholeter gasterophilus''.<ref>Van Waerebeek K, Reyes JC, Alfaro J (1993) [http://www.aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/1993/Aquatic_Mammals_19_3/19-03_VanWaerebeek.pdf "Helminth parasites and phoronts of dusky dolphins Lagenorhynchus obscurus (Gray, 1828) from Peru".] ''Aquat Mamm'' '''19'''(3):159–69.</ref>

 

[[Image:duskyd.jpg|thumb|right|250px|A pair of dusky dolphins breaching]]

Dusky dolphins live in a [[fission-fusion society]] with most group size increases occurring during foraging and decreases in group sizes occurring during resting and traveling. In the Golfo San José off the [[Valdes Peninsula]], dolphins encounter a variety of associates by switching between small traveling groups and large socio-sexual groups. Studies of dolphins off [[Kaikoura]], New Zealand show that dolphins normally live in large groups that split into smaller sub-groups.<ref name = "Markowitz 2004"/> These sub-groups are composed of mating adults (mating groups), mothers with calves (nursery groups) and non-breeding adults.<ref name = "Markowitz 2004"/> Dusky dolphins have a [[promiscuous]] mating system in which both males and females mate with multiple partners. Mating groups are generally made of around ten males and a single female.<ref name = "Markowitz 2004"/> These mating groups can be found in both shallow and deep water but more often gather near shore.<ref name = "mating">Markowitz, T.M.; Markowitz, W.J.; and Morton, L.M. "Mating habits of New Zealand dusky dolphins". Pp. 151–76 in: Würsig, B., and Würsig, M., editors. ''The Dusky Dolphin: Master Acrobat off Different Shores''. Academic Press. (2010) ISBN 0123737230.</ref>{{rp|162}}

[[Image:DuskyJump.jpg|thumb|left|250px|Dusky dolphins leaping]]

 

Dusky dolphins perform a number of aerial displays. Displays include leaps, backslaps, headslaps, tailslaps, spins and noseouts.<ref name= "behavior"/> The dolphins also perform head-over-tail leaps which is considered the most "acrobatic" of the displays.<ref name= "behavior"/> A headfirst re-entry is performed when a dolphin leaps clear out of the water and then arches its back strongly while flipping the tail to make a headfirst re-entry. In "humping", the same motion occurs expect the snout and tail do not leave the water during the arch.<ref name= "behavior"/> Leaps, head-over-tail leaps, backslaps, headslaps, tailslaps and spins often occur in groups. One dolphin starts a particular leap and then continues it 3–20 times.<ref name= "behavior"/> Young dusky dolphins apparently are not born with the ability to perform the leaps and must learn to master each one.<ref name = "calf"/>{{rp|190}} Calves appear to first learn how to perform noisy leaps, followed by head first re-entries, coordinated leaps and finall acrobatic leaps.<ref name = "calf"/>{{rp|190–91}} Adult dusky dolphins may perform different leaps in different contexts and calves may independently learn how to perform leaps but learn when to perform with interactions with others.<ref name = "calf"/>{{rp|191}}

 

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