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song by animals

Animal song is not a well defined term in scientific literature, and the use of the more broadly defined term vocalizations is in more common use. Song generally consists of several successive vocal sounds incorporating multiple syllables. Some sources distinguish between simpler vocalizations, termed “calls”, reserving the term “song” for more complex productions. Song like productions have been identified in several groups of animals, including cetaceans (whales and dolphins), avians (birds), anurans (frogs), and humans. Social transmission of song has been found in groups including birds and cetaceans.

Most mammalian species produce sound by passing air from the lungs across the larynx, vibrating the vocal folds. Sound then enters the supralaryngeal vocal tract, which can be adjusted to produce various changes in sound output, providing refinement of vocalizations. Sound vibrations are conveyed to an organ in the head called the melon, which can be changed in shape to control and direct vocalizations. Unlike in humans and other mammals, toothed whales are able to recycle air used in vocal production, allowing whales to sing without releasing air.

Like mammals, anurans possess a larynx and vocal folds, which are used to create vibrations in sound production. These sacs provide both amplification and fine tuning of sounds, and also allow air to be pushed back into the lungs during vocalizations. The primary vocal organ of birds is called the syrinx, which is located at the fork of the trachea, and is not present in mammals. As air passes through the respiratory tract, the syrinx and the membranes within vibrate to produce sound. Birds are capable of producing continuous song during both inhalation and exhalation, and may sing continuously for several minutes. For example, the skylark (Alauda arvensis) is capable of producing non stop song for up to one hour. Some birds change their song characteristics during inhalation versus exhalation. The Brewer's sparrow (Spizella breweri) alternates between rapid trilling during exhalation interspersed with lower rate trills during short inhalations. The two halves of the syrinx connect to separate lungs, and can be controlled independently, allowing some birds to produce two separate notes simultaneously. Orthopteran insects, including crickets and katydids (family Tettigoniidae), have been especially well studied for sound production. These insects use scraper like structures on one wing to sweep over file structures on an opposing wing to create vibrations, producing a variety of trilling and chirping sounds. Locusts and other grasshoppers (suborder Caelifera) stridulate by rubbing hind legs against pegs on wing surfaces in an up and downward motion. Cicadas (superfamily Cicadoidea) produce sound at much greater volumes than Orthopterans, relying on a pair of organs called tymbals on the base of the abdomen behind the wings. For example, many frogs may use trilling notes in mate attraction, but switch to different vocal patterns in aggressive territorial displays. Bird song is thought to have evolved through sexual selection. Female songbirds often assess potential mates using song, based on qualities such as high song output, complexity and difficulty of songs, as well as presence of local dialect. Song output serves as a fitness indicator of males, since vocalizations require both energy and time to produce, and thus males capable of producing high song output for long durations may have higher fitness than less vocal males. Some species change their courtship calls when females are especially nearby. In male glass frogs (Hyalinobatachium fleichmanni), a long frequency modulated vocalization is produced upon noticing another nearby frog, but is changed to a short chirping song when a female approaches.

Another major function of song output is to indicate aggression among males during breeding seasons. Both anurans and birds use singing in territorial displays to confer aggressive intent. Male frogs typically approach higher frequency sounds more readily than lower frequencies, likely because the frog producing the sound is assessed to be a smaller, less dangerous competitor. Such discrimination is important to mate recognition of many monogamous species. Seabirds, for example, often use vocalization patterns to recognize their mate upon reunion during the breeding season. In many colonial nesting birds, parent offspring recognition is critical to allow parents to locate their own offspring upon return to nesting sites. Cliff swallows (Petrochelidon pyrrhonota) have been demonstrated to preferentially respond to parental songs at a young age, providing a means of vocalization based offspring recognition. In many species, young birds learn songs from adult males of the same species, typically fathers. This was first demonstrated in chaffinches (Fringilla coelabs). Chaffinches raised in social isolation develop abnormal songs, however playing recordings of chaffinch songs allows the young birds to learn their species specific songs. Song learning generally involves a sensitive learning period in early life, during which young birds must be exposed to song from tutor animals in order to develop normal singing as adults. Song learning occurs in two stages: the sensory phase and the sensorimotor phase. During the sensory phase, birds memorize the song of a tutor animal, forming a template representation of the species specific song. For song learning to occur properly, young birds must be able to hear and refine their vocal productions, and birds deafened before the development of subsong do not learn to produce normal adult song. The sensitive period in which birds must be exposed to song tutoring varies across species, but typically occurs within the first year of life. Although most birds acquire song learning within the first year, brown headed cowbirds have a delayed sensitive period, occurring approximately one year after hatching. In other words, the interactive nature of a live tutor seems to trump the familiarity of the recordings from conspecifics.

While vertical transmission (parent offspring) is a common element of song learning, horizontal transmission among animals of the same generation can also occur. Male humpback whales produce various songs over their lifetime, which are learned from other males in the population. Males in a population conform to produce the same mating song, consisting of a highly stereotyped vocal display involved in mate attraction. The cultural transmission of these songs has been found to occur across great geographic distances over years, with one study noting song transmission across the western and central South Pacific Ocean populations over an 11 year period.