Banyak studi yang sudah dilakukan terhadap berbagai aspek burung. Antara lain adalah mengenai “suara burung”. Salah satu buku yang membahas sangat mendalam mengenai aspek suara burung adalah buku “Nature’s Music, The Science of Birdsong” dengan editor Peter Marler dan Hans Slabbekoorn.
Peter Marler adalah peneliti di Department of Neurobiology, Physiology and Behavior University of California Davis California USA, sedangkan Hans Slabbekoorn peneliti di Institute of Biology Leiden University, Leiden, Belanda.
Buku tersebut terdiri dari 14 bab dengan penulis yang berkompeten di bidang masing-masing. Bab 1. Science and birdsong: the good old days oleh Peter Marler; Bab 2. Vocal fighting and flirting: the functions of birdsong oleh Sarah Collins; Bab 3. Learning to sing oleh Henrike Hultsch dan Dietmar Todt; Bab 4. The diversity and plasticity of birdsong oleh Don Kroodsma; Bab. 5. Bird calls: a cornucopia for communication oleh Peter Marler; Bab. 6. Singing in the wild: the ecology of birdsong oleh Hans Slabbekoorn; Bab 7. Audition: can birds hear eveything they sing? Bab. 8. Brains and birdsong oleh Erich D. Jarvis; Bab. 9. How birds sing and why it matters oleh Roderick A. Suthers; Bab. 10. Birdsong and evolution oleh Carel Ten Cate; Bab 11. Performance limits on birdsong oleh Jeffrey Podos and Stephen Nowicki; Bab. 12. Birdsong and conservation oleh Sandra L.L. Gaunt dan D. Archibald McCallum; Bab. 13. Grey parrots: learning and using speech oleh Irene M. Pepperberg; Bab 14. Singing, socializing, and the music effect oleh Meredith J. West, Andrew P. King, dan Michael H. Goldstein.
Sayang sekali buku terbitan Elsevier Academic Press tersebut merupakan karya cipta dengan hak kekayaan intelektual yang dilindungi oleh hukum. Dan karenanya, saya tidak bisa berbagi secara lengkap isinya di sini. Namun demikian, bagian-bagian tertentu dari buku tersebut akan saya gunakan sebagai dasar pijakan ketika menulis artikel tentang burung di website ini.
Tetapi, di samping referensi dalam bentuk buku yang dilindungi HAKI, ada banyak artikel bagus tentang suara burung di website yang bisa kita sharing bareng. Contoh sumber utama artikel bagus dan free bisa disebut di sini adalah wikipedia. Artikel yang menarik di wikipedia tersebut antara lain adalah tentang Bird Vocalization. Anda bisa menyimaknya di link ini: http://en.wikipedia.org/wiki/Bird_vocalization.
Sekadar saran dari saya, ada baiknya Anda pernah membaca artikel tersebut. Untuk Anda yang tidak bisa cepat membaca referensi berbahasa Inggris, tidak perlu repot-repot lagi karena google.com menyediakan sarana penterjemahan yang sangat membantu kita.
Atau kalau Anda tidak ingin repot-repot, silakan baca artikel di bawah ini dan gunakan sarana “terjemahan” yang saya sediakan di bagian samping web ini. Dengan tetap membuka artikel ini, Anda tinggal meng-klik “terjemahkan”, dan Anda pilih gambar bendera “Merah Putih” maka artikel sudah bisa Anda ikuti dalam bahasa Indonesia. Namun ya mohon dimaklumi, karena fasilitas terjemahan versi google ini belum sempurna, kita harus lebih cermat dalam mencernanya. Mau coba? Silakan…
The distinction between songs and calls is based upon inflection, length, and context. Songs are longer and more complex and are associated with courtship and mating, while calls tend to serve such functions as alarms or keeping members of a flock in contact.
Other authorities such as Howell and Webb (1995) make the distinction based on function, so that short vocalizations such as those of pigeons and even non-vocal sounds such as the drumming of woodpeckers and the “winnowing” of snipes’ wings in display flight are considered songs. Still others require song to have syllabic diversity and temporal regularity akin to the repetitive and transformative patterns which define music.
Bird song is best developed in the order Passeriformes. Most song is emitted by male rather than female birds. Song is usually delivered from prominent perches although some species may sing when flying. Some groups are nearly voiceless, producing only percussive and rhythmic sounds, such as the storks, which clatter their bills. In some manakins (Pipridae), the males have evolved several mechanisms for mechanical sound production, including mechanisms for stridulation not unlike those found in some insects.
The production of sounds by mechanical means as opposed to the use of the syrinx has been termed variously instrumental music by Charles Darwin, mechanical sounds and more recently sonation. The term sonate has been defined as the act of producing non-vocal sounds that are intentionally modulated communicative signals, produced using non-syringeal structures such as the bill, wings, tail, feet and body feathers.
The avian vocal organ is called the syrinx; it is a bony structure at the bottom of the trachea (unlike the larynx at the top of the mammalian trachea). The syrinx and sometimes a surrounding air sac resonate to sound waves that are made by membranes past which the bird forces air. The bird controls the pitch by changing the tension on the membranes and controls both pitch and volume by changing the force of exhalation. It can control the two sides of the trachea independently, which is how some species can produce two notes at once.
Scientists hypothesize that bird song has evolved through sexual selection, and experiments suggest that the quality of bird song may be a good indicator of fitness. Experiments also suggest that parasites and diseases may directly affect song characteristics such as song rate, which thereby act as reliable indicators of health.
The song repertoire also appears to indicate fitness in some species. The ability of male birds to hold and advertise territories using song also demonstrates their fitness.
Communication through bird calls can be between individuals of the same species or even across species. Mobbing calls are used to recruit individuals in an area where an owl or other predator may be present. These calls are characterized by wide frequency spectra, sharp onset and termination, and repetitiveness which are common across species and are believed to be helpful to other potential “mobbers” by being easy to locate. The alarm calls of most species, on the other hand, are characteristically high-pitched making the caller difficult to locate.
Individual birds may be sensitive enough to identify each other through their calls. Many birds that nest in colonies can locate their chicks using their calls. Calls are sometimes distinctive enough for individual identification even by human researchers in ecological studies.
Many birds engage in duet calls. In some cases the duets are so perfectly timed as to appear almost as one call. This kind of calling is termed antiphonal duetting. Such duetting is noted in a wide range of families including quails, bushshrikes, babblers such as the scimitar babblers, some owls and parrots. In territorial songbirds, birds are more likely to countersing when they have been aroused by simulated intrusion into their territory. This implies a role in intraspecies aggressive competition.
Some birds are excellent vocal mimics. In some tropical species, mimics such as the drongos may have a role in the formation of mixed-species foraging flocks. Vocal mimicry can include conspecifics, other species or even man-made sounds. Many hypotheses have been made on the functions of vocal mimicry including suggestions that they may be involved in sexual selection by acting as an indicator of fitness, help brood parasites, protect against predation but strong support is lacking for any function. Many birds, and especially those that nest in cavities, are known to produce a snake like hissing sound that may help deter predators at close range.
Some cave-dwelling species, including Oilbird and Swiftlets (Collocalia and Aerodramus spp.), use audible sound (with the majority of sonic location occurring between 2 and 5 kHz) to echolocate in the darkness of caves.
The hearing range of birds is from below 50 Hz (infrasound) to above 20 kHz (ultrasound) with maximum sensitivity between 1 and 5 kHz. The range of frequencies at which birds call in an environment varies with the quality of habitat and the ambient sounds. It has been suggested that narrow bandwidths, low frequencies, low-frequency modulations, and long elements and inter-element intervals should be found in habitats with complex vegetation structures (which would absorb and muffle sounds) while high frequencies, broad bandwidth, high-frequency modulations (trills), and short elements and inter-elements may be expected in habitats with herbaceous cover.
It has been hypothesized that the available frequency range is partitioned and birds call so that overlap between different species in frequency and time is reduced. This idea has been termed the “acoustic niche”. Birds sing louder and at a higher pitch in urban areas, where there is ambient low-frequency noise. (Bersambung)
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