Bottlenose Dolphin
By Jeff Marsch (05/18/09 12:55:10)
Related animal: Dolphin

Behavior:

The bottlenose dolphin normally lives in small groups, usually containing up to 15 animals. However, group size may be highly variable since they live in fission-fusion societies within which individuals associate in small groups that change in composition, often on a daily or hourly basis. Typically, a group of adult females and their young live together in a pod, and juveniles in a mixed pod. Several of these pods can join together to form larger groups of 100 dolphins or more. These groups can occasionally exceed 1000 dolphins. Males live mostly alone or in groups of 2-3 and join the pods for short periods of time.

Bottlenose dolphins studied by researchers of the Bottlenose Dolphin Research Institute BDRI off the island of Sardinia show non-random social behaviour during feeding activities and their social behaviour differs depending on the feeding activity in which they are engaged. In Sardinia, the presence of a floating marine fin-fish farm has been linked to a change in bottlenose dolphin distribution as a result of high fish density around the floating cages in the farming area.

The species sometimes shows curiosity towards humans in or near water. Occasionally, bottlenose dolphins have rescued injured divers by raising them to the surface. This is similar to behaviour they show towards injured members of their own species. In November 2004, a more dramatic report of dolphin intervention came from New Zealand. Four lifeguards, swimming 100 m (328 ft) off the coast near Whangarei, were approached by a shark (reportedly a Great White Shark). A group of bottlenose dolphins, most likely sensing danger to the swimmers, herded them together and tightly surrounded them for forty minutes, preventing an attack from the shark, as they returned to shore.

Dolphins have also been documented exhibiting altruistic behaviour toward other sea creatures. On Mahia Beach, New Zealand on March 10, 2008 two Pygmy Sperm Whales a female and calf became stranded on the beach. Rescuers, including Department of Conservation officer Malcolm Smith, attempted to refloat the whales, however their efforts failed four times. Shortly before the whales were to be euthanized a playful bottlenose dolphin known to local residents as Moko arrived and, after seemingly communicating with the whales, led them 200 meters along a sandbar to the open sea.

The bottlenose dolphin is a predator however, and it also often shows aggressive behaviour. This includes fights among males for rank and access to females, as well as aggression towards sharks, certain Orcas, and other smaller species of dolphins. During the mating season male dolphins compete vigorously with each other through displays of toughness and size with a series of acts such as head-butting. At least one population, off Scotland, has been observed to practice infanticide, and has also been filmed attacking and killing Harbour Porpoises. Researchers at the University of Aberdeen in Scotland have discovered that the local bottlenose dolphins attack and kill Harbour Porpoises without eating them due to competition for a decreasing food supply.

The bottlenose dolphin sometimes forms mixed species groups with certain other species from the dolphin family, particularly larger species such as the Short-finned Pilot Whale, the False Killer Whale and Risso's Dolphin. Interactions with smaller species, such as the Atlantic Spotted Dolphin and the Rough-toothed Dolphin, also occur in wild. While interactions with smaller species are sometimes afffiliative, they can also be aggressive.

Diet:

The bottlenose dolphin's diet consists mainly of small fish and squid.

Communication & Sense:

The dolphin's search for food is aided by a form of echolocation similar to sonar: they locate objects by producing sounds and listening for the echo. A broadband burst pulse of clicking sounds is emitted in a focused beam in front of the dolphin. To hear the returning echo they have two small ear openings behind the eyes but most sound waves are transmitted to the inner ear through the lower jaw. As the object of interest is approached the echo grows louder, and the dolphins adjust by decreasing the intensity of the emitted sounds. (This is in contrast to the technique used by bat echolocation and artificial sonar where the sensitivity of the sound receptor is attenuated.) As the animal approaches the target the interclick interval also decreases, as each click is usually produced after the round-trip travel time of the previous click is completed. Details of the dolphin's echolocation, such as signal strength, spectral qualities, and discrimination abilities have been well-investigated by researchers. Bottlenose dolphins are able to extract shape information from their echolocative sense, suggesting that they are able to form an "echoic image" of their targets.

Dolphins also have sharp eyesight. The eyes are located at the sides of the head and have a tapetum lucidum, or reflecting membrane at the back of the retina, which aids vision in dim light. Their horseshoe-shaped double-slit pupil enables the dolphin to have good vision both in air and underwater, despite the different densities of these media. When underwater the eyeball's lens serves to focus light, whereas in the in-air environment the typically bright light serves to contract the specialized pupil, resulting in sharpness from a smaller aperture (similar to a pinhole camera).

By contrast their sense of smell is poor, as would be expected since the blowhole, the analogue to the nose, is closed in the underwater environment, and opens only voluntarily for breathing. The olfactory nerves as well as the olfactory lobe in the brain are missing. Bottlenose dolphins are able to detect salty, sweet, bitter (quinine sulphate), and sour (citric acid) tastes, but this has not been well-studied. Anecdotally, some animals in captivity have been noted to have preferences for food fish types although it is not clear that this preference is mediated by taste.

Bottlenose dolphins communicate with one another through squeaks, whistles, and body language. Examples of body language include leaping out of the water, snapping jaws, slapping tails on the surface of the water, and butting heads with one another. All of these gestures are a way for the dolphins to convey messages. The sounds and gestures that bottlenose dolphins produce help keep track of other dolphins in the group and alert other dolphins to possible dangers and nearby food. They produce sounds using six air sacs near their blow hole (they lack vocal cords). Each animal has a characteristic frequency-modulated narrow-band signature vocalization (signature whistle) which is uniquely identifying. Other communication uses about 30 distinguishable sounds, and although famously proposed by John Lilly in the 1950s, a "dolphin language" has not been found. However, Herman, Richards, & Wolz demonstrated the comprehension of an artificial language by two bottlenose dolphins (named Akeakamai and Phoenix) in the period of skepticism toward animal language following Herbert Terrace's critique.

Intelligence/cognition:

Cognitive abilities investigated in the dolphin include concept formation, sensory skills, and the use of mental representation of dolphins. Such research has been ongoing from the 1970s. This includes:

* acoustic and behavioral mimicry
* comprehension of novel sequences in an artificial language
* memory
* monitoring of self behaviors
* discrimination and matching
* comprehension of symbols for various body parts
* comprehension of the pointing gesture and gaze (as made by dolphins or humans)
* mirror self-recognition

Recent research has shown that bottlenose dolphins are capable of comprehending numerical values. In an experiment where a dolphin was shown two panels with a various number of dots of different size and position, the dolphin was able to touch the panel with a greater number of dots.

Interaction with humans:

Dolphins have been made to collaborate with humans for a wide variety of commercial and military means throughout the 20th and 21st century. They have also grown to voluntarily interact with humans in the wild. A common instance if such collaboration is playing with surfers near the beach.

In the town of Laguna in south Brazil, a pod of bottlenose dolphins is known to drive fish towards fishermen who stand at the beach in shallow waters. One dolphin will then roll over, which the fishermen take as a sign to throw out their nets. The dolphins feed on the escaping fish. The dolphins were not trained for this behaviour; the collaboration has been going on at least since 1847. Similar cooperative fisheries also exist in Mauritania, Africa.

In the military (actually interesting):

http://www.spawar.navy.mil/sandiego/technology/mammals/mine_hunting.html



[Write Comment]


Comment by marschj (05/18/09 23:07:16):
http://news.nationalgeographic.com/news/2009/04/090408-dolphin-speak-video-ap.html
Comment by marschj (05/18/09 23:06:07):
http://www.thewildclassroom.com/cetaceans/dolphinwhaleecholocation.html