|
Delfiner ~ Biologi
-
-
- GENERAL BIOLOGY
- How do dolphins sleep?
- How intelligent are
dolphins?
How
do dolphins communicate and do they have their own language?
How does dolphin sonar work?
Can
dolphins combine information from their sonar with their vision?
What and how much do
dolphins eat?
How old can they get?
Do dolphins live
shorter in captivity?
How did dolphins evolve?
How can you
interact with wild dolphins?
Why do
whales and dolphins beach themselves?
How deep can dolphins dive?
How fast can dolphins swim?
Where can you find dolphins?
Can dolphins live in
fresh water?
How do dolphins get
their water?
- How do
dolphins make bubblerings?
- DOLPHIN TAXONOMY
- How many
species of dolphins are there?
What
is the dolphin species seen in most oceanaria?
What
species was the dolphin in the Flipper series?
What is the largest dolphin?
What is the
smallest dolphin species?
What
is the difference between dolphins and porpoises?
What are cetaceans?
Are whales and
dolphins endangered?
An
overview of the species of whales and dolphins (the order Cetacea)
Dolphins have to be conscious to breathe (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. 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 behaviour 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 breathe.
Dolphins are said to spend about one-third of their day sleeping/resting,
one-third eating and one-third playing or making love. In our experience
with the dolphins
of Port Stephens there is no fixed pattern; they are often active at
night and at different times of the day.
Sources: 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 and 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
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 generalise (which is also true of pigs, BTW). Also they
can learn to understand complicated language-like commands (which is
also true of the great apes).
The problem is that we try to compare dolphin intelligence with
human intelligence in our usual, homocentric fashion. Given that
dolphins perceive their world in a totally different way to us, and also
live in a totally different world to us, there are no grounds to assume
that their intelligence is in any way like ours. We need to come up with
different ways of measuring their intelligence, instead of trying to
teach them to speak English or use computer keyboards. It has been shown
that dolphins have self-awareness,
and their amazing dexterity and inventiveness is ably illustrated by
their bubble-ring
manipulation.
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 vocalisations 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.
We have heard wild dolphins in the water, using clicks and whistles
to communicate. When you hear the richness and variety of these sounds
it's not difficult to believe that they do indeed have a language. It is
thought that they give each other names, or "signature sounds"
to identify each other. Perhaps they can send sonar "images"
to each other, which would make their language extremely visual and
flexible.
 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).
We believe that the dolphins' sonar is highly sophisticated. Tests
have shown that they can distinguish between two identical-looking
objects with different densities (e.g. solid and hollow spheres), and
containers with complicated shapes inside them. The range of frequencies
used is far wider than we can hear, and sound travels four times faster
in water than in air. Many dolphin therapists (ourselves included!)
believe that the sonar can have a beneficial effect on people,
triggering the release of endorphins and having powerful healing effects.
Of course, the big question is whether the dolphins know
they can do this!
A good link on this topic with a more scientific explanation:
Cole, D.M. (1996) Electroencephalographic
results of human-dolphin interaction: A
sonophoresis model.
The short answer is: yes, they can. Just like people can visualise 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 (visualisation) 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 and C. Reichmuth (1995) Equivalence class
formation and cross-modal transfer: testing marine mammals. In: R.A.
Kastelein, J.A. Thomas and 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 and 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
Bottlenose dolphins eat several kinds of fish (including mullet,
mackerel, herring, cod) and squid. The composition 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 lbw) dolphin will eat 10-22.5 kg
(22-50 lb) fish per day.
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 and 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
No. 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 and D.P.DeMaster (1995) Survival
of five species of captive marine mammals. Marine Mammal Science
11(2):209-226.
How
did dolphins evolve?
The earliest recognisable 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.
Source: P.G.H.Evans (1987) The Natural History of
Whales and Dolphins. Christopher Helm Publishers, London.
When swimming, boating or snorkelling 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. In several areas there are boat operators
that can take you to areas where there is a good chance to encounter
dolphins (Florida, Bahamas). 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' behaviour. 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.
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 occasionally 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, the group leader may be sick and
wash ashore. The other members try to stay close and may 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 behaviour 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 and D.J. St.
Aubin: Biology of marine mammals: Insights through strandings.
Marine Mammal Commission report no: MMC-77/13: pp. 129-188).
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 considerable 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 behaviour 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 and M.D. Scott (1980) The social ecology of
inshore odontocetes. In: L.M. Herman (ed.): Cetacean Behaviour.
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.
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). It is possible that dolphins can reach
speeds over 15 knots during very short bursts (like in preparation for a
high jump), but they can't maintain that speed.
Sources: D. Au and D. Weihs (1980) At high speeds
dolphins save energy by leaping. Nature 284(5756): 548-550
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
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. Christopher Helm Publishers, London.
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. Christopher Helm Publishers, London.
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 metabolise (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.
The family of dolphins (Delphinidae) consists of 32 different
species. Closely related families (the white whales (Monodontidae) and
river dolphins (Platanistidae) have 2 resp. 5 species).
The bottlenose dolphin (Tursiops truncatus).
The killer whale (Orcinus orca). Male killer whales can grow up to
9.6 m (31.5 ft).
There is not really one smallest species. The smallest species
include:
- True dolphins (Delphinidae):
-
Tucuxi (Sotalia fluviatilis) - 1.3 to 1.8 m
-
Hector's dolphin (Cephalorhynchus hectori) - 1.2 to 1.5 m
-
Black dolphin (Cephalorhynchus eutropia) - 1.2 to 1.7 m
-
Commerson's dolphin (Cephalorhynchus commersonii) - 1.3 to 1.7 m
- River dolphins (Platanistidae):
-
Franciscana (Pontoporia blainvillei) - 1.3 to 1.7 m
- Porpoises (Phocoenidae):
-
Vaquita (Phocoena sinus) - 1.2 to 1.5 m
-
Finless porpoise (Neophocaena phocaenoides) - 1.2 to 1.9 m
Dolphins and porpoises belong to different whale families. The most
obvious differences are:
-
dolphins have a falcate (hook-shaped) dorsal fin, whereas
porpoises have a triangular dorsal fin.
-
dolphins have conical teeth; the teeth of of porpoises are spatula
shaped.
-
most dolphin species have a distinct beak. Porpoises don't, giving
their head a more rounded, blunt shape.
Cetaceans is a collective term for whales, dolphins and porpoises.
The name is derived from the scientific (Latin) name of these animals:
Cetacea.
For most species, the answer is probably "No", although it
is very difficult to get a good estimate of the size of populations on
these water living creatures. A number of species are endangered: the
Indus river dolphin, the baiji (there are only about 100 left), the
vaquita, the northern right whale and the blue whale. Another group of
species is listed as "vulnerable" (which means that they are
not in immediate danger of extinction, but also far from safe). These
are: the Ganges river dolphin, the boto, the bowhead, the southern right
whale, the sei whale, the fin whale and the humpback whale.
Source: M. Klinowksa (1991) Dolphins, Porpoises
and Whales of the World The IUCN Red Data Book IUCN, Gland, Switzerland
and Cambridge, U.K.
order CETACEA (WHALES AND DOLPHINS)
suborder MYSTICETI (BALEEN WHALES)
family BALAENIDAE (RIGHT WHALES)
Eubalaena glacialis (northern right whale)
Eubalaena australis (southern right whale)
Balaena mysticetus (bowhead whale)
Caperea marginata (pygmy right whale)
family BALAENOPTERIDAE (FIN WHALES or RORQUAL
WHALES)
Balaenoptera musculus (blue whale)
Balaenoptera physalus (fin whale)
Balaenoptera borealis (sei whale)
Balaenoptera edeni (Bryde's whale)
Balaenoptera acutorostrata (minke whale)
Megaptera novaeangliae (humpback whale)
family ESCHRICHTIIDAE (GRAY WHALES)
Eschrichtius robustus (gray whale)
suborder ODONTOCETI (TOOTHED WHALES)
family PHYSETERIDAE (SPERM WHALES)
Physeter macrocephalus (sperm whale)
Kogia breviceps (pygmy sperm whale)
Kogia simus (dwarf sperm whale)
family ZIPHIIDAE (BEAKED WHALES)
Berardius bairdii (Baird's beaked whale)
Berardius arnuxii (Arnoux' beaked whale)
Tasmacetus shepherdi (Shepherd's beaked whale)
Ziphius cavirostris (Cuvier's beaked whale)
Hyperoodon ampullatus (northern bottlenose whale)
Hyperoodon planifrons (southern bottlenose whale)
Mesoplodon pacificus (Longman's beaked whale)
Mesoplodon hectori (Hector's beaked whale)
Mesoplodon mirus (True's beaked whale)
Mesoplodon europaeus (Gervais' beaked whale)
Mesoplodon ginkgodens (ginkgo-toothed beaked whale)
Mesoplodon grayi (Gray's beaked whale)
Mesoplodon carlhubbsi (Hubbs' beaked whale)
Mesoplodon stejnegeri (Stejneger's beaked whale)
Mesoplodon bowdoini (Andrew's beaked whale)
Mesoplodon bidens (Sowerby's beaked whale)
Mesoplodon layardii (strap-toothed whale)
Mesoplodon densirostris (Blainville's beaked whale)
Mesoplodon peruvianus (Pygmy beaked whale)
Mesoplodon bahamondi (Bahamonde's beaked whale)
family DELPHINIDAE (DOLPHINS)
Steno bredanensis (rough-toothed dolphin)
Sousa chinensis (Indo-Pacific hump-backed dolphin)
Sousa teuszii (Atlantic hump-backed dolphin)
Sotalia fluviatilis (tucuxi)
Tursiops truncatus (bottlenose dolphin)
Stenella longirostris (spinner dolphin)
Stenella clymene (clymene dolphin)
Stenella frontalis (Atlantic spotted dolphin)
Stenella attenuata (pantropical spotted dolphin)
Stenella coeruleoalba (striped dolphin)
Delphinus delphis (common dolphin)
Lagenodelphis hosei (Fraser's dolphin)
Lagenorhynchus albirostris (white-beaked dolphin)
Lagenorhynchus acutus (Atlantic white-sided dolphin)
Lagenorhynchus obliquidens (Pacific white-sided dolphin)
Lagenorhynchus obscurus (dusky dolphin)
Lagenorhynchus australis (Peale's dolphin)
Lagenorhynchus cruciger (hourglass dolphin)
Cephalorhynchus commersonii (Commerson's dolphin)
Cephalorhynchus heavisidii (Heaviside's dolphin)
Cephalorhynchus eutropia (black dolphin)
Cephalorhynchus hectori (Hector's dolphin)
Lissodelphis borealis northern (right whale dolphin)
Lissodelphis peronii southern (right whale dolphin)
Grampus griseus (Risso's dolphin)
Peponocephala electra (melon-headed whale)
Feresa attenuata (pygmy killer whale)
Pseudorca crassidens (false killer whale)
Globicephala melaena (long-finned pilot whale)
Globicephala macrorhynchus (short-finned pilot whale)
Orcinus orca (killer whale)
Orcaella brevirostris (Irrawaddy dolphin)
family MONODONTIDAE (WHITE WHALES)
Delphinapterus leucas (beluga, white whale)
Monodon monoceros (narwhal)
family PLATANISTIDAE (RIVER DOLPHINS)
Platanista gangetica (Ganges river dolphin)
Platanista minor (Indus river dolphin)
Inia geoffrensis (boto, Amazon river dolphin)
Lipotes vexillifer (baiji, Yangtze river dolphin)
Pontoporia blainvillei (franciscana, La Plata dolphin)
family PHOCOENIDAE (PORPOISES)
Phocoena phocoena (harbor porpoise)
Phocoena sinus (vaquita)
Phocoena dioptrica (spectacled porpoise)
Phocoena spinnipinnis (Burmeister's porpoise)
Neophocaena phocaenoides (finless porpoise)
Phocoenoides dalli (Dall's porpoise)
Main source: M. Klinowksa (1991) Dolphins,
Porpoises and Whales of the World The IUCN Red Data Book IUCN, Gland,
Switzerland and Cambridge, U.K.
~ Delfinterapi
Facts Links
Hvemervi Kontakt
Home ~
Opdated Feb. 2005, Dolphin
Consult
|
