Dolphins and Echolocation

By: Colleen Murray
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1. Background:

Class: Mammal
Order: Cetacean
Origin: Green word for "delphis" which meals "fish with womb"
Species: 40 different species

2. Comparisons: Dolphins vs. Porpoises

Dolphins and Porpoises are almost identical to the naked eye. There are four main differences between the two which include: number of species, length and weight, teeth, and mobility. There are forty different species of dolphins that range from four to thirty feet and are between nintey pounds and ten tons. Dolphins have conical milk teeth and have impressive neck mobility. Porpoises on the other hand, have only six species which are five to five and half feet, ranging from one hundred thirty-five pounds to one hundred seventy pounds. Porpoises have flattened teeth and fused neck vertebrae which limits their neck mobility.

Bottle-Necked Dolphin
Bottle-Necked Dolphin

3. Anatomy

Dolphins have streamlined, hairless bodies that allow them to be fast swimmers. They have a total of five fins which include: the dorsal fin, located on the top side of the dolphin, fluke fins are on the back bottom part of the tail and help dolphins dive or leap out of the water, and the pectoral fins are located on either side of the dolphins body. Pectoral fins resemble a human arm and these fins along with the fluke fins help to direct a dolphin. Dolphins have a melon in their heads which gives them their unique echolocation ability. Dolphins have elongated jaws that form its famous beak and they are able to breathe through a blow hole which is located on top of their bodies.

4. Five Sense

Dolphins are very intelligent, sophisticated animals who have four of the five senses. Dolphins have very good eyesight. They are able to see well above water and deep in the ocean. Dolphins have nerve endings which gives them the ability to have a sense of touch. Dolphins are unable to smell because they do not have an olfactory nerve which allows mammals to smell. Dolphins hear ten times the frequencies of humans and this directly relates to their unique sonar/echolocation ability. Dolphins have a sense of taste and some specific species prefer different types of fish in comparison to other species.

5. Mannerisms

Dolphins are very social animals so they travel in pods of about twelve. It is not uncommon for pods to join together in an area that has a wealth of food to form superpods. Dolphins are very caring and protective creates who care for sick or injured dolphins. They are also known to take care of other animals in the sea, and there have been occassions when dolphins have helped humans. Dolphins love to jump, fake fight, and ride waves. They are very playful, happy creatures. Dolphins mostly feed on fish and squid. Scientists have noticed that specific species have different feeds regiments. Dolphins sleep with one brain hemisphere are a time. this helps them to continue to breathe and watch for predators. These sleeping patterns change if dolphins are in captivity. If they are in captivity they tend to sleep with both brain hempisheres relaxed because they do not have to worry about predators.

6. Echolocation

Dolphins have a unique sonar ability which allows them to communicate with one another. Dolphins use air sacs located near the blowhole and nasal sacs located behind the melon to make whistle and click noises which are then projected from the front of the dolphin. These noises travel through the water and help dolphins locate food, search for prey, and ultimately make a map of the ocean. Sound travels four and a half times faster in water than in air so this complex process is completed relatively quickly. Once the sound reaches an object, it bounces back towards the dolphin and is received and analyzed through their sonar ability. The information received enters the "acoustic window," travels to the middle ear and then reaches the melon where the information can be processed.

7. Threats

Although dolphins are relatively large mammals, they face several threats in the open sea waters. Sharks hunt seals and dolphins for food and killer whales have been known to kill other species of dolphins as well. Dolphin drive hunting is the hunting of dolphins for their skin and meal. This practice is especially popular in Japan. There are many protest groups against this practice. Dolphins that are captured during drive hunting are also transported to dolphinariums where they are put on display.


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