Studies of Bird Intelligence Through Speech and Vocalization
Studies of Bird Intelligence Through Speech and Vocalization
Abstract: Studies of Bird Intelligence through Speech and Vocalization
Birds posses a respiratory and nervous system sharing similarities with the human species. Some of these similarities between birds and human beings are even closer than similarities between human beings and chimpanzees. This coupled with a high degree of intelligence allows many birds to go beyond normal songs and vocalization, enabling mimicry of many sounds and words and perhaps even the basic use of language. The evolutionary advantage of singing and mimicry is not quite known, but most researchers agree there must be a survival advantage. The degree of bird intelligence is debated, giving rise to a number of interesting studies on the cognitive ability of these animals.
Human beings vibrate the vocal cords, located near the larynx, with the help of the tongue and lips to form words. Though birds possess a larynx, they actually use a structure known as the syrinx, located in the throat, to make sounds and vocalizations (4). The syrinx is basically the equivalent of the human voice box, which is located above the trachea. However, the syrinx is located farther down, at the junction of two bronchi leading to the lungs, resulting in two potential sound sources (5). The syrinx has two identical structures called medial tympaniform membranes, which create sound by producing a flow of air in the throat that creates sound waves (4). The muscles of the syrinx control sound production; birds with more intricate vocal muscles produce more complex sounds. Other structures in the respiratory system, including air sacs, aid in the vibrations the lead to sound and speech. The result is a variety of sounds with much greater range than can be attained by human beings (5).
Aside from the respiratory system, songbirds, hummingbirds, and parrots share brain patterns similar to human beings. This includes development of unique receptors at several different places on the brain. This shared brain structure helps explain the evolution of vocal learning (3). There appears to be some connection between the visual and auditory apparatus shared by human beings and birds, yet this connection is absent with apes or chimpanzees. This, along with a lack of necessary intracerebral connections, may explain the chimpanzee’s restricted use of its vocal apparatus (6).
Bird songs are a means for communicating over long distances, especially when the birds are not visible to each other due to lack of light or dense vegetation. Birds vary the sounds they make based on their environment. A constant brief signal works best in forests where sound bounces off trees. If the intended recipient doesn’t hear the first time, they will surely catch the sound’s echo. Birds on the forest floor use low-pitched calls that will not be bounced off and distorted by the ground. Species living in plains use the buzz, a compressed message which carries over great distances in open areas. Some birds, such as the blue-black grassquit, will actually transmit their signal above objects by jumping up and calling in mid-air (5).
Most birds from a wide variety of locations show the greatest amount of singing activity around dawn (5); this is also when companion bird speech peaks (4). Some believe this is the best time for sound to travel due to little wind and fewer other noise disturbances. By singing at dawn when energy reserves are low, male birds may be communicating to females that they are still able to breed (5).
Because noise attracts unwanted attention from predators, birds must have a good reason for singing. Two known reasons for singing include the desire to attract a mate and also the need to defend one’s territory. Males use an operatic song pattern to attract a mate by singing long elaborate songs to which females generally do not respond. The more complex the song, the better chance of a male attracting a female. Birds maintaining year-long territory often sing in duets because it helps maintain contact between members of a pair. Sometimes, birds defend their territory together in a group chorus. Each bird contributes its own phrase, producing a song that sounds as if only one bird is singing. On the contrary, some individual birds, such as the sparrow weavers, produce a song the sounds as complex as one coming from nine birds (5).
Birds in the wild learn to mimic their parents and other adults of their species soon after they are hatched. Birds are most likely to imitate sounds they hear regularly, especially higher frequency sounds and voices that seem to interest them (4). The best mimics include mockingbirds, starlings, mynahs, marsh warblers, lyrebirds, bowerbirds, scrub-birds and African robin-chats (5). The mynahs are known for their ability to mimic the songs of other bird species. Because