Song and Calls

Birdwatching Fundamentals 4 ended its method with sound as step five. Often it is the first clue: many birds are heard long before they are seen, and some similar species are easier to tell apart by voice than by looks. This chapter covers the difference between songs and calls, how a bird produces and learns sound, the dawn chorus, and the tools people use to describe and record what they hear.

Songs and Calls

Wikipedia's Bird vocalization article says songs are longer and more complex and tied to territory and courtship, while calls usually serve as alarms or keep flocks in contact. It adds that some authorities classify by function instead, so that short vocalisations such as a pigeon's count as song. The earlier-cited article on identification by sound gives the same split by "complexity, length, and context".

How Birds Make Sound

The article names the vocal organ as the syrinx, "a bony structure at the bottom of the trachea". Birds control pitch through membrane tension, and both pitch and volume through the force of exhalation. The two sides of the trachea can be controlled independently, which lets some species produce two notes at once.

Learning to Sing

According to the article, juveniles go through sensory learning (memorising a tutor's song) and sensorimotor learning (practising until the output matches the memory). Early singing is "sub-song", followed by "plastic song", then a stable "crystallized song" after "two or three months". It reports that Thorpe (1954) found isolated birds produce less complex songs, and that dialects arise as young birds learn details from their fathers. Zebra finches are described as age-limited learners and canaries as open-ended learners.

Repertoires and Mimicry

The Dawn Chorus

Wikipedia's Dawn chorus article defines it as "the outbreak of birdsong at the start of a new day", most noticeable in spring in temperate countries. It lists hypotheses for it: defending a territory, attracting a mate, or calling to the flock. Anders Pape Møller's playback experiments on black wheatears raised singing in both the same and other species, which he suggested was "social facilitation". A 2007 study in an Ecuadorian forest found that birds perched higher in the trees and with larger eyes tended to sing first, which the article suggests may reflect differences in the light they perceive. The article does not give a time relative to sunrise, so none is stated here. It also gives the first Sunday in May as International Dawn Chorus Day (check that this is still the current date).

Hearing Range and Loud Birds

• Birds hear from below 50 Hz to about 12 kHz, with maximum sensitivity at 1–5 kHz (Bird vocalization article).
• The black jacobin produces sounds at about 11.8 kHz and the western capercaillie uses infrasound at about 20 Hz.
• The white bellbird's call reaches 125 dB against 116 dB for the screaming piha, a 9 dB difference (125 minus 116).
• Oilbirds and swiftlets echolocate mainly between 2 and 5 kHz.

Describing and Recording Sound

Birders write sounds as words. The article gives the white-throated sparrow as "O sweet Canada Canada Canada" in Canada and "Old Sam Peabody Peabody Peabody" in New England, and the barred owl as "Who cooks for you? Who cooks for you all?". Such phrases are called mnemonics (the term is my label; check).

A sonogram (spectrogram) is a visual record of sound. The article says sonograms are objective, unlike descriptive phrases, but need experience to interpret. It says the Sona-Graph was marketed in 1948 and that C.E.G. Bailey demonstrated it for bird song in 1950. It also says Ludwig Koch made the first known birdsong recording in 1889, at age eight; that would put his birth year at 1881 (1889 minus 8), which I have not checked elsewhere (check). Today's apps match recordings against databases of spectrograms, per the article on identification by sound.

Not Yet Verified, and Sources

• Sources. The Bird vocalization page: the first 100,000 characters of about 222,700 were read through the fetch tool, which returned a summary, so later sections are unread. The Dawn chorus page was also a summary.
• Not in the articles. The word "mnemonics", the advice to write down what you hear, and the playback caution (check).
• Left open. Whether International Dawn Chorus Day is still held on the first Sunday in May, and Koch's birth year.

Exercises