Animal song

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. 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. Although morphological differences between species affect sound production, neural control is thought to be more essential factor in producing the variations within human speech and song compared to those of other mammals. Cetacean vocalizations are an exception to this general mechanism. Toothed whales (Odontocetes) pass air through a system of air sacs and muscular phonic lips, which vibrate to produce audible vocalizations, thus serving the function of vocal folds in other mammals. 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. Some cetaceans, such as humpback whales, sing continuously for hours. Like mammals, anurans possess a larynx and vocal folds, which are used to create vibrations in sound production. However, frogs also use structures called vocal sacs, elastic membranes in the base of the mouth which inflate during 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. This allows air used in sound production to be recycled, and is thought to have evolved to increase song efficiency. Increased efficiency of sound production is important, as some frogs may produce calls lasting for several hours during mating seasons. The New River tree frog (Trachycephalus hadroceps), for example, spends hours producing up to 38,000 calls in a single night, which is made possible through the efficient recycling of air by the vocal sac. When birds inhale, air is passed from the mouth, through the trachea, which forks into two bronchii connecting to the lungs. 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. Insects such as crickets (family Gryllidae) are well-known for their ability to produce loud song, however the mechanism of sound production differs greatly from most other animals. Many insects generate sound by mechanical rubbing of body structures, a mechanism known as stridulation. 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 a 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. Muscle contraction rapidly deforms the tymbal membrane, emitting several different types of sounds. Insects thus produce a variety of sounds, using various mechanisms distinct from other animals. Vocalizations can play a wide variety of different roles. In groups such as anurans and birds, several distinct types of notes are incorporated to form songs, which are sung in different situations and serve distinct functions. For example, many frogs may use trilling notes in mate attraction, but switch to different vocal patterns in aggressive territorial displays. In some species, a single song incorporates several note types which serve different purposes, with one type of note eliciting responses from females, and another note of the same song responsible for warning competitor males of aggression. Vocalizations play an important role in the mating behaviour of many animals. In many groups (birds, frogs, crickets, whales etc.), song production is more common in males of the species, and is often used to attract females. 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. It is thought that song complexity may serve as an indicator of male fitness by providing an indication of successful brain development despite potential early-life stressors, such as lack of food. Social transmission of songs allows for development of local dialects of song, and female songbirds also typically prefer to choose mates producing local song dialects. One hypothesis for this phenomenon is that selecting local mates allows the female to choose genes specially adapted to suit local conditions.