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alt.animals.dolphins FAQ (part 1 of 3) |
Selected newsgroup headersNewsgroups: alt.animals.dolphins,alt.answers,news.answers Subject: Dolphin FAQ (1/3) Summary: General and biology section of alt.animals.dolphins FAQ Approved: news-answers-request@MIT.EDU Archive-name: animals/dolphin-faq/part01 Posting-Frequency: monthly Last-modified: 2002/03/14 Maintainer: Jaap van der Toorn <jaap@rosmarus.com> This is part 1 of the FAQ for alt.animals dolphins. This document is maintained by Jaap van der Toorn ( jaap@rosmarus.com). 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. |
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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:
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).
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:
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.
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.
See also the echolocation section in the Dolphin Basics page
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.
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).
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.
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.
A survival guide to survival rates (online paper). This paper is also available for download in Acrobat (.PDF) format
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.
A survival guide to survival rates (online paper). This paper is also available for download in Acrobat (.PDF) format
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).
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). 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)
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:
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.
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).
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.
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).
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.
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