How do Dolphins sleep?
Dolphins have to be conscious to breathe. 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. 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 can vary within different species of Dolphins, and possibly on individual preferences. They can either: - swim slowly and surface every now and then for a breath which is the pattern for the Hawaiian Spinner Dolphins - 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.
How intelligent are Dolphins?
During the past few decades, scientists have intensified their efforts to better understand the Dolphin mind. This research led to a groundbreaking milestone in 2001. A study conducted at the Wildlife Conservation Society’s New York Aquarium demonstrated unequivocally that Dolphins are self-aware, a complex, cognitive capacity previously known only in humans and great apes (Reiss & Marino, 2001). But just how intelligent are they? The short answer to this is that we do not yet 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, BTW). Also they can learn to understand complicated language-like commands (which is also true of the great apes).
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.
DOLPHINS may be closer to humans than previously realised, with new research showing they communicate by whistling out their own “names”. The evidence suggests Dolphins share the human ability to recognise themselves and other members of the same species as individuals with separate identities. The research, on wild bottlenose Dolphins, will lead to a reassessment of their intelligence and social complexity, raising moral questions over how they should be treated. The research was carried out by Vincent Janik of the Sea Mammal Research Unit at St. Andrews University, who has found bottlenose Dolphins to be among
the animal world’s quickest learners of new sounds.
He said: “Each animal develops an individually distinctive signature whistle in the first few months of its life, which appears to be used in individual recognition.”
The research has its origin in the 1960s when Dolphin trainers first noticed that captive animals each had their own personal repertoire of whistles. This prompted speculation that Dolphins had their own language and might even have individual “names”. However, the theory was controversial among whale and Dolphin researchers, and until now, there had been no means of testing it.
Janik’s work was based on a group of Dolphins living in Sarasota Bay, Florida, who have been studied for more than 30 years. Over that time researchers have built up a detailed picture of individual Dolphins, their family ties and their “social” interaction. They have also made extensive recordings of the noises made by individual Dolphins and isolated the sounds thought to be their “signature whistles” or names.
In the study some of the Sarasota Bay animals were corralled in a net. The researchers then played synthetic versions of the signature whistles of other Dolphins through underwater loudspeakers to see if they would evoke a response in the captive animals. The use of synthetic whistles ruled out the possibility that the animals might simply be recognising the sound of each other’s voices. They found that Dolphins responded strongly to the whistles of their relatives and associates while generally ignoring those of Dolphins to whom they had no link.
Janik said: “Bottlenose Dolphins are the only animals other than humans to have been shown to transmit identity information independent of the caller’s voice.”
The findings are supported by other authorities. Denise Herzing, research director at the Wild Dolphin Project at Florida Atlantic University, said it was already clear that many of the 77 known cetacean (whale and Dolphin) species had rudimentary languages. “We know that Dolphins’ brains are nearly as large and complex, relative to body size, as those of humans. They have evolved to be intelligent and that implies being able to communicate,” she said. Dolphins may, however, be just the first of many species where individuals are found to have their own names. Other researchers have already found evidence for highly developed language skills in parrots, crows and primates.
Great apes, such as chimpanzees and orang-utans, have been a popular subject for research because they are so closely related to humans. Their limited vocal apparatus means they cannot speak but researchers at Georgia State University have taught chimpanzees to communicate in English via computers equipped with customised keyboards and voice synthesizers. The African grey parrot is another renowned linguist, able not only to learn words but to use them in the right context.
Even some rodent species may have developed a rudimentary language. Con Slobodchikoff of Northern Arizona University recently found that prairie dogs, a large rodent found in the western United States, shared a language of at least 100 words. Donald Broom, professor of animal welfare at Cambridge University, said species living in large groups all had advanced communication skills. “They have a complex social structure where they have to live with others, negotiate friendships and find mates. If Dolphins are using names I expect we will find the same in other species with similar lifestyles.”.
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.
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.
What and how much do Dolphins eat?
Dolphins eat several kinds of fish 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 per day.
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 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.
How fast can Dolphins swim?
The Dolphin's fast cruising speed (a travelling speed they can maintain for quite a while) is about 11 - 12.5 km/hr. They can reach speeds of up to 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 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 between6.0 - 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. 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.
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 preferred 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.
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).
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 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.
