Editing Cetacean surfacing behaviour (section)

=== Porpoising ===
<gallery widths="250px" heights="220px">
File:Hourglas dolphin crop.jpg|[[Hourglass dolphin]]s in [[Drake Passage]]
File:Anim0796 - Flickr - NOAA Photo Library.jpg|[[Southern right whale dolphin]]s porpoising
</gallery>
''Porpoising'', also known as running,<ref name="OH4">{{Citation|title=At high speeds dolphins save energy by leaping. |date=1980 |first1=D. |last1=Au |first2=D. |last2=Weihs |journal=Nature |volume=284 |issue=5756 |pages=548–550 |doi=10.1038/284548a0|bibcode=1980Natur.284..548A |s2cid=4334691 }}</ref> is a high speed surface behaviour of small cetaceans where long jumps are alternated with swimming close to the surface. Despite the name, porpoising behaviour is seen in dolphins and porpoises, as well as other marine species such as [[penguins]]<ref name="OH5">{{Citation|title=The porpoising of penguins an energy-conserving behaviour for respiratory ventilation? |first1=C. A. |last1=Hui |year=1987 |journal=Canadian Journal of Zoology |volume=65 |pages=209–211 |doi=10.1139/z87-031}}</ref> and [[pinnipeds]].<ref name="OH6">{{Citation|title=Dynamics of dolphin porpoising revisited |first1=D. |last1=Weihs |journal=Integrative and Comparative Biology |year=2002 |volume=42 |issue=5 |pages=1071–1078 |doi=10.1093/icb/42.5.1071 |pmid=21680390|doi-access=free }}</ref> When [[marine mammals]] are travelling at speed they are forced to stay close to the surface in order to maintain [[Breathing|respiration]] for the energetic exercise. At leisurely cruising speeds below 4.6&nbsp;m/s, dolphins swim below the water's surface and only briefly expose their [[blowhole (anatomy)|blowholes]] along with up to one third of their body at any one time.<ref name="OH4" /> This results in little splashing as they have a very streamlined shape.<ref name="OH6" /> Porpoising occurs mainly when dolphins and porpoises are swimming at speeds greater than 4.6&nbsp;m/s.<ref name="OH4" /> Here, jump length is roughly equal to distance traveled when the cetaceans are submerged.<ref name="OH4" /> This exposes the blowhole for longer which is needed to get enough oxygen to maintain [[metabolism]] and therefore high speeds over long periods of time. Studies have also shown that leaping is more energetically efficient than swimming above a certain threshold speed.<ref name="OH4" /> This is due to the reduction in friction when travelling in air compared to water which saves more energy than is needed to produce the leap.<ref name="OH6" /> These benefits also outweigh the energy wasted due to the large amount of splashing often seen when groups are porpoising.<ref name="OH4" /> Porpoising is therefore a result of high speed swimming which cetaceans use for important pursuit and escape activities. For example, dolphins may be seen porpoising away from their main predator, [[sharks]]<ref name="test 6">{{Citation|title=Shark attacks on bottlenose dolphins (Tursiops aduncus) in Shark Bay, Western Australia: attack rate, bite scar frequencies, and attack seasonality |journal=Marine Mammal Science |pages=526–539 |volume=17 |issue=3 |year=2001 |first1=M. R. |last1=Heithaus |doi=10.1111/j.1748-7692.2001.tb01002.x|bibcode=2001MMamS..17..526H }}</ref> or the direction of incoming boats to avoid collision.<ref name="test_7">{{Citation|title=Effects of tour boats on the behavior of bottlenose dolphins: using Markov chains to model anthropogenic impacts |year=2003 |first1=D. |last1=Lusseau |journal=Conservation Biology |volume=17 |issue=6 |pages=1785–1793 |doi=10.1111/j.1523-1739.2003.00054.x|bibcode=2003ConBi..17.1785L |s2cid=83589031 }}</ref>

Although porpoising is a useful product of rapid swimming, much variation seen in the behaviour cannot be explained by this cause alone; it has likely evolved to provide other functions. For example, the rotation during porpoising by the [[spinner dolphin]] leads to much splashing and is more common at slower speeds<ref name="OH4" /> so cannot be attributed to an energy saving mechanism. It is therefore more likely to be a form of play or communication within or between pods.<ref name="OH4" /> Another reason might be to remove [[barnacles]] or [[remora]]s that, when attached, increase drag during swimming.<ref name="test_10">{{Citation|title=Mechanics of remora removal by dolphin spinning |year=2007 |journal=Marine Mammal Science |volume=23 |issue=3 |pages=707–714 |first1=D. |last1=Weihs |first2=F. E. |last2=Fish |first3=A. J. |last3=Nicastro |doi=10.1111/j.1748-7692.2007.00131.x|bibcode=2007MMamS..23..707W }}</ref> When spinner dolphins impact the water the combination of [[centrifugal force|centrifugal]] and vertical force upon these [[ectoparasites]] can be up to 700 times their own weight and so efficiently remove them.<ref name="test_10" /> Other theories suggest that cetaceans may porpoise in order to observe distant objects such as food by looking for visual cues, such as birds dive-bombing a [[bait ball]].<ref name="test_8">[http://www.dolphins-world.com/why-do-dolphins-jump-out-of-the-water/], "Why do dolphins jump out of the water?", Dolphin World FAQ.</ref> Research into the additional functions of porpoising has so far been focussed on the more acrobatic species, but it is likely that other cetaceans also use it for these, and perhaps unknown, reasons too.