Echolocation

------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- Title: Echolocation in marine mammals ------------------------------------------------- ------------------------------------------------- Name: Fiona Howlin ------------------------------------------------- ------------------------------------------------- Student Number: 8152578 ------------------------------------------------- ------------------------------------------------- Word count: 500 ------------------------------------------------- ------------------------------------------------- Date: 22 Nov 2011 ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- ------------------------------------------------- Summary Echolocation is the biological sonar used by several kinds of animals including some mammals and a few birds; most notably microchiropteran bats and odontocetes (toothed whales and dolphins). Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation and for foraging (or hunting) in various environments. Cetacea is a scientific order of large aquatic mammals that have forelimbs modified into flippers, a horizontally flattened tail, one or two nostrils at the top of the head for breathing, and no hind limbs. Living cetaceans are further divided into two suborders: the Odontoceti (toothed whales) and the Mysticeti (baleen whales). Dolphins are part of the suborder Odontoceti.  | Dolphins use clicks as their bisonar signal, which are produced in rapid sequence, called "click trains".  The frequency range for echolocation clicks is 0.2 to 150 kHz (Reynolds & Rommel, 1999).  Because lower frequency sounds travel further, dolphins tend to use lower frequencies when echolocating on objects that are at a distance. Lower frequency clicks, however, do not deliver as much detailed information about an object as higher frequency clicks. Thus, as the dolphin moves closer to an object, it can increase the frequency of its echolocation to learn more about the object. The dolphin’s echolocation system can identify an object as small as a ping pong ball as far away as 100 yards. The site of sound production appears to be the museau de singe or “monkey lips” which resemble the lips of monkeys (Cranford et al., 1997).  These sounds produced by the monkey lips will travel in the forward direction through the melon.  The fatty tissue melon located in the forehead area of the dolphin acts like an acoustic lens directing the sound out (Au et al., 2000). The clicks emitted by a dolphin strike objects in its underwater world and bounce back as echoes to be picked up through the dolphin's lower jaw (Norris, 1968).  From the returning echoes, a dolphin can tell the size, shape, distance from, speed, direction of travel, and density of the object. Even in a large group of dolphins all echolocating at once, each dolphin seems to be able to pick out its own echolocation echoes and not collide with another (Au et al., 2000). Interestingly enough, scientists now speculate that a dolphin’s teeth may play a part in receiving incoming echolocation pulses. The teeth are perfectly spaced one tooth space apart from each other, and the teeth on one side of the jaw are aligned one half of a tooth space forward than the other side of the jaw. It is believed that this arrangement of the teeth acts as an array or antenna focusing the incoming sound and helping the dolphin pinpoint the exact location of an object (Goodson & Klinowska, 1990).  References Au, W. 1993. The Sonar of Dolphins. New York: Springer-Verlag. Au, W., A.N. Popper, and R. F. Fay, ed. 2000. Hearing by Whales and Dolphins. New York: Springer-Verlag. Cranford TW. Van Bonn WG, Chaplin MS, Carr JA, Kamolnick TA, Carder DA, Ridgway SH (1997).  Visualizing dolphin sonar signal generation using high-speed video endoscopy.  Journal Accoustics Society of America 102:3123 Goodson AD, Klinowski M (1990) A proposed ceholocation receptor for the bottlenose dolphin, Tursiops truncatus: modeling the receive directivity from tooth and lower jaw geometry.  In: Thomas JA, Kastelein RA (eds) Sensory Abilities of Cetaceans: Laboratory and Field Evidence, New York: Plenum Press, pp 255-268. National Research Council of the National Academies, 2005, Marine Mammal Populations and Ocean Noise, The National Academies Press, Washington, D.C. Norris KS (1968) The evolution of acoustics mechanisms in odontocete cetaceans.  In: Drake ET (ed) Evolution and Enviornment.  New Haven: Yale University Press, pp. 297-324. Ocean Noise Has Increased Considerably Since 1960’s.  According to New Scripps Analysis, Scripps Institution of Oceanography/UC San Diego, August 18, 2006.  Reynolds, J.E., Wells, R., and Eide, S., 2000 The Bottlenose Dolphin, University Press of Florida Ridgway SH, Carder DA, Green RF, Gaunt AS, Gaunt SLL, Evans WE (1980) Electromygraphic and pressure events in the nasolaryngeal system of dolphins during sound production.  In: Bussnel RG, Fish JF (eds) Animal Sonar Systems.  New Yourk: Plenum, pp 239-249. Tyack, P. 1999. Communication and cognition. Pages 287-323 in Reynolds, III, J. E. and S. A. Rommel (eds.). Biology of Marine Mammals. Washington D. C.: Smithsonian Institution Press.