Dolphins Essay Research Paper Bottlenose dolphins are

Dolphins Essay, Research Paper

Bottlenose dolphins are among the most vocal of the nonhuman animals and

exhibit remarkable development of the sound production and auditory

mechanisms. This can be seen in audition, which is shown in the animal.s

highly refined echolocation ability, and in tightly organized schools in which

they live that are made up by sound communication. In testing the

communication skills of dolphins, extensive studies have been done on vocal

mimicry, in which the animal imitates computer-generated sounds in order to

test motor control in terms of cognitive ability. Language comprehension on

the other hand has been tested through labeling of objects, which has proven

to be successful regarding the association of sound and object stimulus. The

biggest question in dolphin communication, is whether or not the species is

capable of intentional communicative acts. Though results from studies have

been debatable, the key to understanding the extent to this .language. is to

determine whether they have a repertoire of grammatical rules that generate

organized sequences. In determining this, the greatest accomplishment for

both the scientist and all of humanity, would be to accomplish interspecies

communication, creating a bridge between humans and animals which could

open up a new understanding of the unknown world of wildlife. Most

importantly, it is necessary to understand the incredible aptitude of dolphin

communicative skills, and the impressive intelligence the animal possesses

which allows for a great deal of intraspecies and interspecies communication

(Schusterman, Thomas, & Wood, 1986). The acoustical reception and

processing abilities of the bottlenosed dolphins have generally been shown to

be among the most sophisticated of any animal so far examined (Popper,

1980 as cited by Schusterman et al. 1986). In order to understand the

complexity of these highly mechanized acoustic systems, it is necessary to

learn the process for which the dolphin hears. In most water-adapted

cetaceans, tissue conduction is the primary route of sound conduction to the

middle ear. The isolation of the bullae shows an adaptation for tissue

conducted sound. The lower jaw contains fat that is closely associated with

the impedance of seawater. The lower jawbone of most odontocetes

becomes broadened and quite thin posteriorly, and the fat forms an oval

shape that closely corresponds to the area of minimum thickness of the jaw.

This fat body leads directly to the bulla, producing a sound path to the ear

structures located deep within the head. Paired and single air sacs are

scattered throughout the skull, which serve to channel these tissue-conducted

sounds (Popov & Supin, 1991). Other than this description, there are still

more studies needed to determine the function of the middle ear and the type

of bone conduction that occurs within the bulla. Due to detailed audiograms,

dolphins have been shown to have the ability to detect high-frequency

sounds. In an experiment by Johnson (1966) as cited in Schusterman et al.

(1986), sine-wave sounds ranging in frequency from 75 Hz to 150 Hz were

presented to a bottle-nosed dolphin. The animal was trained to swim in a

stationary area within a stall and to watch for a light to come on. Following

the light presentation a sound was sometimes presented. If the dolphin heard

the sound, its task was to leave the area and push a lever. Sound intensity

levels were varied by a staircase method of 1, 2, or 3 dB steps. The resulting

audiogram, compared to the human aerial audiogram, showed that at regions

of best sensitivity for each, thresholds for human and dolphin are quite similar,

but separated by about 50 kHz in frequency, showing that the animal.s inner

ear function is very similar to a human. The experiments done on dolphin

auditory functions have generally shown a finely adapted sound reception

system. This would be expected due to the highly adapted echolocation

ability of the bottlenosed dolphin and other cetaceans. Results of work on

absolute thresholds, critical bandwidths, frequency discrimination, and sound

localization all indicate that the dolphin auditory system is at least as good or

better than the human system. This is in spite of the fact that sound travels five

times as fast under water as it does in air (Popov et al. 1991). The

bottlenosed dolphin in captivity produces two categories of vocalizations: (a)

narrow-band, frequency-varying, continuous tonal sounds referred to as

.whistles. and (b) broad-band pulsed sounds expressed as trains of very

short duration clicks of varying rates (Evans, 1967, as cited in Schusterman

et al. 1986). The pulsed sounds are used for both communication and

echolocation, and the whistles are found to be used primarily for

communication (Herman & Tavolga, 1980, as cited in Schusterman et al.

1986). Descriptions in literature em

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