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* This is part 1 of the FAQ for alt.animals dolphins.
* This document is maintained by Jaap van der Toorn
* ([e-mail]). The intention is to post the latest
* version of the FAQ on the newsgroup once a month.
*
* Please direct any remarks, suggestions, corrections and
* additions to the above e-mail address.
*
* Last update: March 14, 2002
*

1.0 - What is alt.animals.dolphins?

  alt.animals.dolphins is an unmoderated newsgroup for anyone
  interested in dolphins. Unmoderated means that no-one is
  screening the messages before they are put on the newsgroup.
  As a result, you may occassionally see messages on that have
  nothing to do with dolphins. Usually these are advertisements
  for (often dubious) services and get-rich-fast schemes.
  The best way to deal with those is just to ignore them. Do
  not post follow-up messages and do not mail to the sender.
  This will only encourage them to post more messages in the
  future.

  Topics that are suitable for this newsgroups include (but
  are not restricted to): requests for information, exchanges
  of experiences and ideas, news items etc. as long as they
  relate to dolphins and/or whales.

  Do not post pictures in this newsgroup. These are usually
  large and this is not very polite to readers of the group
  that have to pay connection time fees. If you want to make
  pictures available through Usenet, post them in the designated
  newsgroup: alt.binaries.pictures.animals. You can then post
  a short announcement in this group that you have made them
  available there.

  This group is not intended for lengthy discussion on
  political issues, even though these may deal with dolphins.
  A better platform for these discussions is the newsgroup
  talk.politics.animals.

  For issues dealing with large whales, there is a separate
  newsgroup: alt.animals.whales. Not every provider forwards
  its messages, however.

2.0 - GENERAL BIOLOGY

2.1 - How do dolphins sleep?

  Dolphins have to be conscious to breath (Williams et al, 1990).
  This means that they cannot go into a full deep sleep, because
  then they would suffocate.
  Dolphins have "solved" that by letting one half of their brain
  sleep at a time. This has been determined by doing EEG studies
  on dolphins. Dolphins sleep about 8 hours a day in this fashion.
  Recent research confirmed that dolphins have only one eye
  closed when sleeping. The state (open or closed) of one eye
  remains constant for on average an hour, after which it
  switches state (Goley, 1999).
  REM (Rapid Eye Movement) sleep, usually associated with
  dreaming has been recorded only very rarely. Some scientists
  claim dolphins do not have REM sleep at all.

  A dolphin's behavior when sleeping/resting depends on the
  circumstances and possibly on individual preferences. They
  can either:
  - swim slowly and surface every now and then for a breath
  - rest at the surface with their blowhole exposed
  - rest on the bottom (in shallow water) and rise to the surface
    every now and then to breath.


  sources:
  P.D. Goley (1999)
    Behavioral aspects of sleep in Pacific whitesided dolphins
    (Lagenorhynchus obliquidens, Gill 1865)
    Marine Mammal Science 15(4): 1054-1064

  S.H Ridgway (1990)
    The Central Nervous System of the Bottlenose Dolphin,
    in S. Leatherwood and R.R. Reeves: The Bottlenose Dolphin,
    pp. 69-97, Academic Press

  Th.D. Williams, A.L. Williams & M. Stoskopf (1990)
    Marine Mammal Anesthesia. In: L.A. Dierauf (ed.): Handbook
    of Marine Mammal Medicine: Health, Disease and Rehabilitation,
    pp. 175-191 CRC Press, Boca Raton


2.2 - How intelligent are dolphins?

  The short answer to this is that we do not know. There is no
  reliable method to measure intelligence in humans across
  cultures, so it is not surprising that comparing humans,
  dolphins, apes, dogs, etc. is impossible. There are some
  indications of their potential: they are fast learners and
  can generalize (which is also true of pigs, apes). Also they
  can learn to understand complicated language-like commands
  (which is also true of the great apes).

  Suggested reading:
  R.P. Balda, I.M. Pepperberg & A.C. Kamil (eds.) (1998)
     Animal cognition in nature - The convergence of psychology
     and biology in laboratory and field.
     Academic Press, San Diego, London
  R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.) (1986)
     Dolphin cognition and behavior: a comparative approach,
     Lawrence Erlbaum Associates, New Jersey

2.3 - How does the dolphin brain compare to the human brain?

  Whales and dolphins have quite large brains. Most authors
  agree that the size should be viewed in relation to the body
  size. In some comparisons, brain weight to body weight ratio
  is used, but it is now more common to use the so-called
  Encephalization Quotient (EQ), which is calculated as:
    EQ = brain weight / (0.12 * (body weight ^ (2/3)))
  (brain weight, divided by 0.12 time the body weight to the
  power (2/3)). In this formula, brain and body weight should be
  expressed in grammes. In bottlenose dolphins, the EQ lies
  between 4 and 5, in the killer whale between 2.5 and 3, in
  humans in the 6.5-7.5 range.

  However, the structure of the dolphin brain is quite different
  from most land mammals and shows a lot of similarities with
  so-called archetypal mammals like hedgehogs and bats (mammals in
  which the brain structure has changed little since the middle of
  the Tertiary period).

  Dolphin and whale ancestors returned to the sea 50-70 million years
  ago. (Bats have presumably developed their aerial lifestyle in the
  same period). In their adaptation to the aquatic environment, they
  seem to have retained characteristic features of the brain of the
  primitive mammalian species of the time. In cetaceans, the neocortex
  has expanded greatly, but without the substantial reorganization
  in 6 layers seen in most land mammals. The main features in the
  cetacean brain which differ from land mammals are:
  - a thin neocortex (about 1.5 mm, compared to 2.9 mm in humans)
  - rather uniform structure of the cortex
  - low degree of differentiation between cortical layers and cells
  - massive development of the (phylogenetically older) layers I and VI
  - poor development of layers II, III and IV (which are well developed
  in land mammals)
  - the neurons have relatively few primary dendrites and these are
  weakly branched.

  References and suggested reading:
  A. Berta & J.L. Sumich (1999)
     Marine mammals - Evolutionary biology
     Academic Press, San Diego, London
     (ch. 7.3 focuses on senses and the nervous system)
  I.I. Glezer, P.R. Hof, C. Leranth & P.J. Morgane (1992)
     Morphological and histochemical features of odontocete visual
     neocortex: immunocytochemical analysis of pyramidal and
     non-pyramidal populations of neurons.
     in: J.A. Thomas, R.A. Kastelein & A.Y. Supin (eds.):
     Marine Mammal Sensory Systems, pp. 1-38
     Plenum Press, New York, London
  L. Marino (1997)
     The relationship between gestation length, encephalization,
     and body weight in odontocetes.
     Marine Mammal Science 13(1):133-138
  P.J. Morgane, M.S. Jacobs & A. Galaburda (1986a)
     Evolutionary morphology of the dolphin brain
     in: R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.):
     Dolphin cognition and behavior: a comparative approach,
     pp. 5-29
     Lawrence Erlbaum Associates, New Jersey
  P.J. Morgane, M.S. Jacobs & A. Galaburda (1986b)
     Evolutionary aspects of cortical organization in the
     dolphin brain.
     in: M.M. Bryden & R. Harrison (eds.):
     Research on Dolphins, pp. 71-98
     Oxford Science Publications, Clarendon Press, London
  P.J. Morgane & I.I. Glezer (1990)
     Sensory neocortex in dolphin brain
     in: J.A. Thomas & R.A. Kastelein (eds.):
     Sensort Abilities of Cetaceas - Laboratory and Field Evidence,
     pp, 107-136. NATO ASI Series, Series A: Life Sciences vol. 196
     Plenum Press, New York, London
  S.H. Ridgway (1986a)
     Physological observations on dolphin brains
     in: R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.):
     Dolphin cognition and behavior: a comparative approach,
     pp. 31-59
     Lawrence Erlbaum Associates, New Jersey
  S.H. Ridgway (1986b)
     Dolphin brain size
     in: M.M. Bryden & R. Harrison (eds.):
     Research on Dolphins, pp. 59-70
     Oxford Science Publications, Clarendon Press, London

2.4 - How do dolphins communicate and do they have their own
      language?

  Dolphins communicate mainly by means of sounds. These
  sounds include whistles, but also so-called pulsed sounds,
  which are often described as squawks, barks, rasps, etc.
  But they also use breaching (jumping and falling back into
  the water with a loud splash) and pectoral fin (or flipper)
  and tail (or fluke) slaps (hitting the flipper or fluke on
  the water surface). Body posturing and jaw popping also have
  a role in communication. This list is not exhaustive.

  As for language, we do not know if they have one. Several
  studies have demonstrated that dolphins can understand a
  structured language like ours. This same has been demonstrated
  for a number of other animals species as well (gorilla, bonobo,
  California sea lion, parrot). Some studies also indicate that
  dolphin vocalizations are complex enough to support some form
  of language. However, to date it has not been demonstrated yet
  that they indeed use a language for communication among
  themselves.

  Suggested reading:
  R.P. Balda, I.M. Pepperberg & A.C. Kamil (eds.) (1998)
     Animal cognition in nature - The convergence of psychology
     and biology in laboratory and field.
     Academic Press, San Diego, London
  R.J. Schusterman, J.A. Thomas & F.G. Wood (eds.) (1986)
     Dolphin cognition and behavior: a comparative approach,
     Lawrence Erlbaum Associates, New Jersey

2.5 - How does dolphin sonar work?

  Dolphins (and other toothed whales) can produce high pitched
  clicks. When these clicks hit an object, some of the sound
  will echo back to the "sender". By listening to the echo and
  interpreting the time it took before the echo came back, the
  dolphin estimate the distance of the object. (That's why sonar
  is also called echolocation: with information from the echoes,
  a dolphin can locate an object). Depending on the material the
  object is made of, part of the sound may penetrate into the
  object and reflect off internal structure. If the object is a
  fish, some sound will reflect off the skin on the dolphin's
  side, some of the bones, the internal organs and the skin on
  the other side. So one click can result in a number of (weaker)
  echoes. This will give the dolphin some information about the
  structure and size of the fish. By moving its head (thereby
  aiming the clicks at other parts of the fish) the dolphin
  can get more information on other parts of the fish.

  It is like a medical ultrasound probe, but the results are far
  less clear. A medical probe moves back and forth very rapidly,
  much faster than a dolphin can move its head. Also the
  frequency of the sounds of the medical probe is much higher
  than a dolphin's sonar. Therefore the level of detail
  the echoes can provide is much higher in the medical probe.

  For technical information on dolphin sonar, check out the
  following book:
  W.W.L.Au (1993)
    The sonar of dolphins.
    Springer-Verlag New York

2.6 - Can dolphins combine information from their sonar with
      their vision?

  The short answer is: yes, they can. Just like people can
  visualize an object by just touching it, dolphins can get an
  idea of what an object looks like by scanning it with their
  sonar. They can also identify objects with their sonar that
  they have only been able to see. If they form a visual picture
  from the sonar information (visualization) or form an
  acoustical picture from visual information is still unresolved.
  This capability is called cross-modal transfer and it has been
  demonstrated in only a few animal species so far: the
  bottlenose dolphin and the California sea lion.
  See the following references for more details on this subject.

  R.J. Schusterman, D. Kastak & C. Reichmuth (1995)
  Equivalence class formation and cross-modal transfer:
  testing marine mammals.
  In: R.A. Kastelein, J.A. Thomas & P.E. Nachtigall (eds):
  Sensory systems of Aquatic Mammals, pp. 579-584
  De Spil Publishers, Woerden, the Netherlands
  ISBN 90-72743-05-9

  A.A. Pack & L.M. Herman (1995)
  Sensory integration in the bottlenosed dolphin: Immediate
  recognition of complex shapes across the senses of
  echolocation and vision
  J. Acoustical Society of America 98(2) Part 1: 722-733

2.7  - Can dolphins see colors?

  To able to see colors, the retina must have at least 2
  different kinds of cones, with different sensitivities.
  Most mammals have 2 types of cones: L-cones (sensitive to
  long-wavelength light, red to green) and S-cones (sentitive
  to short-wavelength light, blue to violet or near UV). Humans
  and some other primates have 3 types of cones, giving them a
  better color vision. Only a few landmammals have only one
  type of cone, which means they are colorblind. All these
  landmammals are essentially nocturnal animals.

  Whales and dolphins (as well as seals and sea lions) have
  only one type of cone: the L-cones. Although these cones are
  more sensitive for short-wavelength light than the L-cones
  of terrestrial mammals, they still have a very low sensitivity
  for blue light. And because there is only one type of cone,
  they are essentially colorblind (although in theory it is
  possible that there is a very limited form of colorvision
  in some light conditions, when both the rods and the cones
  are active).

  Reference:
  L. Peichl, G. Behrmann & R.H.H. Kr÷ger (2001)
  For whales and seals the ocean is not blue: a visual pigment
  loss in marine mammals
  European Journal of Neuroscience, vol. 13: 1520-1528


2.8 - What and how much do dolphins eat?

  Bottlenose dolphins eat several kinds of fish (including
  mullet, mackerel, herring, cod) and squid. The compostion of
  the diet depends very much on what is available in the area
  they live in and also on the season.
  The amount of fish they eat depends on the fish species they
  are feeding on: mackerel and herring have a very high fat
  content and consequently have a high caloric value, whereas
  squid has a very low caloric value, so to get the same energy
  intake (calories) they will need to eat much more if they feed
  on squid than if they feed on mackerel or herring.
  On average an adult dolphin will eat 4-9% of its body weight
  in fish, so a 250 kg (550 lb) dolphin will eat 10-22.5 kg
  (22-50 lb) fish per day.


2.9 - How old can they get?

  The maximum age for bottlenose dolphins is between 40 and 50
  years. The average age a dolphin can get (the life expectancy)
  can be calculated from the Annual Survival Rate (the percentage
  of animals alive at a certain point, that is still alive one
  year later). For the dolphin population in Sarasota Bay, the
  ASR has been measured to be about 0.961. This yields a life
  expectancy of about 25 years. For the population in the
  Indian/Banana River area, the ASR is between 0.908 and 0.931.
  This yields a life expectance between 10.3 and 14 years.
  So the actual life expectancy differs per region.

  sources:
  R.S. Wells & M.D. Scott (1990)
    Estimating bottlenose dolphin population parameters from
    individual identification and capture-release techniques.
    Report International Whaling Commission (Special Issue 12):
    407-415

  S.L.Hersch, D.K.Odell & E.D.Asper (1990)
    Bottlenose dolphin mortality patterns in the Indian/Banana
    River System of Florida, in S. Leatherwood and R.R. Reeves:
    The Bottlenose Dolphin, pp. 155-164, Academic Press


2.10 - Do dolphins live shorter in captivity?

  There is no evidence to support that statement.
  A recent study, comparing the survival of dolphins in
  captivity from 1940 through 1992 showed no significant
  difference in ASR between the "captive population" and the
  Sarasota Bay population. The ASR for the captive population
  was 0.944 (life expectancy: 17.4 years).
  Also in captivity dolphins have reached ages over 40 years.

  source:
  R.J.Small & D.P.DeMaster (1995)
    Survival of five species of captive marine mammals.
    Marine Mammal Science 11(2):209-226.


2.11 - How did dolphins evolve?

  The earliest recognizable cetaceans lived about 50 million
  years ago. These evolved from the Mesonychids: large land
  mammals, some of which were carnivorous, some herbivorous.
  The earliest cetaceans were members of the now extinct family
  Archaeoceti (the best known of which are Zeuglodon and
  Basilosaurus). 38-25 million years ago the Archaeoceti
  disappeared and were replaced by the early Odontocetes (toothed
  whales) and Mysticetes (baleen whales). The earliest dolphins
  appeared in the late Miocene period, some 11 million years ago.

  The land animals that are closest to whales and dolphins are
  the Ungulates (hoofed animals). This was determined among
  others by comparing the structure of body proteins. The closest
  relative is probably the hippopotamus (Ursing and Arnason, 1998).

  sources:
  P.G.H.Evans (1987)
    The Natural History of Whales and Dolphins.
    Christoper Helm Publishers, London.
  B.M. Ursing & U. Arnason (1998)
    Analyses of mitochondrial genomes strongly support
    a hippopotamus-whale clade
    Proceedings of the Royal Society of London B 265: 2251-2255


2.12 - How can you interact with wild dolphins?

  When swimming, boating or snorkling in certain areas you can
  encounter wild dolphins. Keep in mind that in the US it is
  illegal to directly approach dolphins. If dolphins come
  towards you and choose to interact, that is allowed. Always
  check the local regulations for interactions with wildlife!
  In several areas there are boat operators that can take you
  to areas where there is a good chance to encounter dolphins
  (Florida, Bahamas, Hawaii, but also Norway and Iceland).

  A note of warning: there have been operators that have tried
  to lure dolphins by feeding them. This is illegal in the US
  and is highly undesirable, because it changes the dolphins'
  behavior. Currently there are operators offering bird-feeding
  tours. These bird feedings take place in areas frequented
  by dolphins and are an attempt to circumvent the dolphin
  feeding ban. Do not use these operators.

  Also note that there is some evidence that swimming with
  wild dolphins may change their behavior (Scarpaci et al, 2001)

  Source:
  C. Scarpaci, S.W. Bigger, P.J. Corkeron & D. Nugegoda (2001)
    Bottlenose dolphins (Tursiops truncatus) increase whistling
    in the presence of 'swim-with-dolphin' tour operations
    Journal of Cetacean Research and Management 2(3): 183-185


2.13 - Why do whales and dolphins beach themselves?

  If a single whale or dolphin strands, it usually is a very
  sick (and exhausted) animal. Such an animal often has some
  infections (pneumonia is almost always one of them) and a lot
  of parasites (worms in the nasal passages are very common).
  Sometimes these animals can be rehabilitated, but often they
  are so sick they won't make it.
  Some species of whales and dolphins occassionally strand in
  groups. A stranding of 2 or more animals is usually called a
  mass stranding. There are a number of theories that try to
  explain the occurrence of mass strandings. No theory can
  adequately explain all of them. In some cases it will be a
  combination of causes. The most common explanations are:
  - deep water animals (the species that most often are the
    victim of mass strandings) can not "see" a sloping sandy
    beach properly with its sonar. They detect the beach only
    when they are almost stranded already and they will panic
    and run aground.
    source:
    W.H. Dudok van Heel (1962):
      Sound and Cetacea. Neth. J. Sea Res. 1: 407-507
  - whales and dolphins may be navigating by the earth's
    magnetic field. When the magnetic field is disturbed (this
    occurs at certain locations) the animals get lost and may
    run into a beach.
    source:
    M. Klinowska (1985):
      Cetacean live stranding sites relate to geomagnetic
      topography. Aquatic Mammals 11(1): 27-32
  - in some highly social species, it may be that when the
    the group leader is sick and washes ashore, the other members
    try to stay close and eventually strand with the group leader.
    source:
    F.D. Robson (?)
    The way of the whale: why they strand.
    (unpublished manuscript)
  - when under severe stress or in panic, the animals may fall
    back to the behavior of their early ancestors and run to
    shore to find safety.
    source:
    F.G. Wood (1979)
    The cetacean stranding phenomena: a hypothesis.
    In: J.B. Geraci & D.J. St. Aubin: Biology of marine
    mammals: Insights through strandings. Marine Mammal
    Commission report no: MMC-77/13: pp. 129-188

2.14 - How deep can dolphins dive?

  The deepest dive ever recorded for a bottlenose dolphin was a
  300 meters (990 feet). This was accomplished by Tuffy, a
  dolphin trained by the US Navy. Most likely dolphins do not
  dive very deep, though. Many bottlenose dolphins live in fairly
  shallow water. In the Sarasota Bay area, the dolphins spend a
  considarable time in waters that are less than 2 meters
  (7 feet) deep. Other whale and dolphin species are able to
  dive to much greater depths even. The pilot whale
  (Globicephala melaena) can dive to at least 600 meters (2000
  feet) and a sperm whale (Physeter macrocephalus) has been found
  entangled in a cable at more that 900 meters (500 fathoms)
  depth. Recent studies on the behavior of belugas
  (Delphinapterus leucas) has revealed that they regulary dive
  to depths of 800 meters. The deepest dive recorded of a beluga
  was to 1250 meters.

  sources:
  F.G. Wood (1993)
    Marine mammals and man. R.B. Luce, Inc., Washington.
  E.J. Slijper (1979)
    Whales, 2nd edition. Cornell University Press, Ithaca, NY.
    (Revised re-issue of the 1958 publication: Walvissen, D.B.
    Centen, Amsterdam).
  R.S. Wells, A.B. Irvine & M.D. Scott (1980)
    The social ecology of inshore odontocetes. In: L.M. Herman
    (ed.): Cetacean Behavior. Mechanisms & functions,
    pp. 263-317. John Wiley & Sons, New York
  A.R. Martin (1996)
    Using satellite telemetry to aid the conservation and wise
    management of beluga (Delphinapterus leucas) populations
    subject to hunting.
    Paper presented at the 10th Annual Conference of the European
    Cetacean Society, March 11-13, 1996, Lisbon, Portugal.

2.15 - How fast can dolphins swim?

  The dolphin's fast cruising speed (a travelling speed they can
  maintain for quite a while) is about 3-3.5 m/s (6-7 knots,
  11-12.5 km/hr). They can reach speeds of up to 4.6 m/s
  (9.3 knots, 16.5 km/hr) while travelling in this fashion. When
  they move faster, they will start jumping clear of the water
  (porpoising). They are actually saving energy by jumping.
  When chased by a speedboat, dolphins have been clocked at
  speeds of 7.3 m/s (14.6 knots, 26.3 km/hr), which they
  maintained for about 1500 meters, leaping constantly.

  Energetic studies have shown, that the most efficient
  travelling speed for dolphins is between 1.67 and 2.27 m/s
  (3.3-4.5 knots, 6.0-8.2 km/hr).

  There have been reports of dolphins travelling at much higher
  speeds, but these refer to dolphins being pushed along by the
  bow wave of a speeding boat. They were getting a free ride
  (their speed relative to the surrounding water was low).
  A recent study using based on the vertical speed during
  jumps showed maximum speeds for bottlenose dolphins of
  8.2-11.2 m/s (16-22 knots, 29.5-40.3 km/hr) prior to a high
  jump. The maximum speed for wild bottlenose dolphins was
  5.7 m/s (11 knots, 20.5 km/hr) and for common dolphins
  6.7 m/s (13 knots, 24.1 km/hr).

  sources:
  D. Au & D. Weihs (1980)
    At high speeds dolphins save energy by leaping.
    Nature 284(5756): 548-550

  J.J.Rohr, F.E.Fish and J.W. Gilpatrick, Jr. (2002)
    Maximum swim speeds of captive and free-rangings
    delphinids: critical analysis of extraordinary
    performance
    Marine Mammal Science 18(1):1-19

  T.M.Williams, W.A.Friedl, J.A. Haun & N.K.Chun (1993)
    Balancing power and speed in bottlenose dolphins (Tursiops
    truncatus) in: I.L. Boyd (ed.): Marine Mammals -
    Advances in behavioural and  population biology,
    pp. 383-394. Symposia of the Zoological Society
    of London No. 66. Clarendon Press, Oxford

2.16 - Where can you find dolphins?

  Whales and dolphins can be found in almost every sea and ocean,
  from the Arctic ocean, through the tropics all the way to the
  Antarctic. Each species however has its own prefered type of
  habitat. Some live cold water only, others in tropical oceans
  only. There are also species that can be found in a large
  variety of environments, like the bottlenose dolphins, killer
  whales and sperm whales.

  source:
  P.G.H.Evans (1987)
    The Natural History of Whales and Dolphins.
    Christoper Helm Publishers, London.


2.17 - Can dolphins live in fresh water?

  There are a number of dolphin species that live in fresh water.
  They all belong to the river dolphin families. These are:
  the Platanistidae (Ganges and Indus river dolphins), the
  Iniidae (the boto or Amazon river dolphin) and the
  Pontoporiidae (the baiji and the franciscana). There is one
  species that can be found both in fresh water (the Amazon
  river) and in coastal sea waters: the tucuxi (Sotalia
  fluviatilis).
  In general, salt water species don't do well in fresh water.
  They can survive for some time, but they will be come
  exhausted (since they have less buoyancy in fresh water) and
  after a while their skin will start to slough (like our own
  skin after spending a long time in the bathtub).

  source:
  P.G.H.Evans (1987)
    The Natural History of Whales and Dolphins.
    Christoper Helm Publishers, London.

2.18 - How do dolphins get their water?

  Most dolphins live in the ocean and the ocean water is too
  salty for them to drink. If they would drink sea water, they
  would actually use more water trying to get rid of the salt
  than they drank in the first place. Most of their water they
  get from their food (fish and squid). Also, when they
  metabolize (burn) their fat, water is released in the process.
  Their kidneys are also adapted to retaining as much water as
  possible. Although they live in water, they have live as
  desert animals, since they have no direct source of drinkable
  water.