Zebra finches are commonly studied in captivity by biologists
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The morning chorus of birds has captivated poets and nature enthusiasts for centuries, yet the reasons behind this daily ritual remain unclear.
Recent experiments on zebra finches (Teniopygia guttata) indicate that even though darkness suppresses their songs, these birds experience a heightened inclination to sing at night, culminating in vocal bursts once night descends. Furthermore, the study implies that practicing their vocalization in daylight enhances their singing performance.
Satoshi Kojima and his team from the Korea Brain Research Institute in Daegu, South Korea, examined zebra finches raised in a lab with carefully controlled lighting to alter their light-dark schedules.
Initially, they postponed the bright light exposure for the finches by three hours from natural dawn. Under the fabricated darkness, the birds were awake yet silent, but once the light activated, they chirped more energetically than usual.
When the lights were turned on three hours prior to actual dawn, the finches resumed singing, although not as fervently as before.
Kojima explains that a longer delay between the birds waking and the onset of light results in a more intense dawn chorus.
“The birds remain awake in the dark before light arrives,” he notes. “Their natural inclination to sing is hindered by darkness, and this suppression amplifies their eagerness to sing, leading to a surge in singing immediately after the lights come on.”
The researchers subsequently trained the birds to pull a lever for 10 seconds of artificial light. When the simulated dawn was postponed by three hours, the birds engaged with the lever more often; conversely, when it was advanced, they used the lever less frequently.
The scientists administered Luzindole, a drug that counteracts melatonin, which is released at night and regulates awake cycles in numerous animals. Finches treated with the drug five hours before their normal light time awakened earlier and began to sing sooner than those given a saline solution.
Kojima and his colleagues also scrutinized the finches’ songs to observe alterations throughout the day. They discovered a notable shift in song structure between the first and second hours after dawn.
“Due to the lack of singing at night, the vocal motor system and song acoustic structure may experience slight degradation, but the dawn chorus rapidly restores or enhances them,” Kojima remarks.
While this research focused on a single species, Kojima believes that analogous factors could influence other birds. “Considering the simplicity of these mechanisms and their functional implications, we propose that they may underlie dawn choruses across various avian species.”
However, Diego Gil from the National Museum of Natural Sciences in Madrid, Spain, advises caution. “There are numerous differences among species regarding the how, when, and what they sing during their dawn chorus,” he says. “This diversity accounts for the 11 different hypotheses put forth to explain the phenomenon.”
Gill commended the study, noting that it demonstrates an increased inclination for birds to sing during pre-dawn hours. “If zebra finches experience extended nights without singing, they become more motivated to vocalize,” he explains. “They also indicate that these prolonged nights exceed their sleep requirements, prompting them to sing when given the chance.”
However, the study does not conclusively show that the purpose of the dawn chorus is to refine the birds’ songs, Gill adds. “Although these song structure alterations are believed to enhance the vocalization, there is no data to confirm that females favor these changes,” he notes. “The study merely suggests that songs evolve gradually over time.”
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Source: www.newscientist.com
