Experiments with zebra finches suggest that darkness suppresses birds' singing motivation overnight, leading to an intense dawn chorus when light arrives. The research also indicates that this singing helps optimize vocal structures. While promising, experts caution that the findings may not fully explain the phenomenon across all species.
The dawn chorus, a global phenomenon where birds burst into song at first light, has long puzzled scientists. A new study by Satoshi Kojima at the Korea Brain Research Institute in Daegu, South Korea, and his colleagues offers mechanistic and functional insights using laboratory-raised zebra finches (Taeniopygia guttata) under controlled lighting conditions.
In one experiment, researchers delayed sudden bright light by three hours past actual dawn. The finches remained awake but silent in the artificial darkness. When lights finally turned on, the birds sang more intensely than usual. Conversely, advancing lights by three hours still triggered a chorus, but with reduced intensity. Kojima explained: “The birds are already awake in the dark before the lights come on. But their spontaneous singing is suppressed by the darkness. This suppression elevates their motivation to sing, leading to a high rate of singing as a rebound immediately after the lights are turned on.” The longer the delay between waking and light onset, the more fervent the singing became.
Birds were also trained to press a lever for 10 seconds of artificial light. They pressed frequently when daylight was delayed by three hours but rarely when advanced. Administering luzindole, which blocks melatonin—a hormone regulating wakefulness—five hours before normal lights-on time caused finches to wake quicker and sing earlier compared to those given a saline injection.
Analysis of songs revealed rapid structural changes in the first hour after dawn versus the second. Kojima noted: “Due to the absence of singing during the night, the vocal motor system and song acoustic structure may slightly deteriorate, and the dawn chorus serves to quickly restore or optimise them.”
The team proposes these mechanisms could apply broadly to other birds. However, Diego Gil at the National Museum of Natural Sciences in Madrid, Spain, urges caution, citing myriad species differences and 11 existing hypotheses. He acknowledged the study's cleverness in showing built-up motivation from extended dark periods but criticized the lack of evidence that song changes improve appeal to females: “The study just shows that song changes progressively with singing time.”
The findings are detailed in a bioRxiv preprint (DOI: 10.1101/2025.09.29.679172).