On cold mornings, birds don't sing — The reason why the mountain dawn becomes "quiet" has been discovered

The Moment When the "Obvious" at Dawn Crumbles

In the early mornings of spring and summer, birds engage in a "dawn chorus," where they sing in competition with each other. While it may seem a bit noisy to humans, for birds, this is a crucial "battle time" during the breeding season. However, in the mountains, this chorus suddenly falls silent under certain conditions—a phenomenon that a research team in the field of "soundscape ecology," which interprets ecosystems through sound, has uncovered. Phys.org

The setting is South Africa's Golden Gate Highlands National Park. Known for its high elevation and harsh winters, it is part of the Drakensberg Mountains, bordering Lesotho. Researchers tracked how the timing of birds beginning to sing changes with the weather in this "cold mountain wetland." Phys.org

The Main Characters: The "Warbler" Trio of the Wetlands

The subjects of the study are three closely related species of small insectivorous songbirds that live in wetland reed beds. Phys.org

• Little rush warbler (Bradypterus baboecala)

• African yellow warbler (Iduna natalensis)

• Lesser swamp warbler (Acrocephalus gracilirostris)

All of these species are widely distributed in southern Africa and can be found not only in mountain wetlands but also in reed beds near residential ponds and dams. During the breeding season, they actively participate in the dawn chorus. Phys.org

What Exactly is the "Dawn Chorus"?

The dawn chorus is a phenomenon where multiple bird species in a habitat sing intensively around sunrise. In the Southern Hemisphere, the chorus season generally spans September to February, with the primary purpose being "mate searching" during the breeding season. In many cases, males sing vigorously, and females may respond. Phys.org

The chorus doesn't mean "everyone sings at the same time." To stand out, each species may adjust their singing time and frequency (pitch), leading to an "acoustic niche" rather than a spatial one. While it may sound chaotic to humans, to the "judges" (females of the same species), it sounds appealing—the research article explains. Phys.org

Research Method: Collecting "Sound" Without Human Presence

A key point of this study is that researchers did not stay in the mountain wetlands to observe; instead, they set up automated recording devices to collect sound over a long period. These devices captured bird calls over long distances and durations, recording the dawn chorus "from start to finish." Phys.org

To extract specific bird calls from the recording data, the study used an analysis software called Kaleidoscope Pro. Additionally, they combined data from nearby weather stations (temperature, humidity, wind, rain) with online lunar phase information to mathematically evaluate which factors influence the "start of singing." Phys.org

Results: Cold Mornings Really Are "Quiet"

To conclude, this was common to all three species.

• The warmer the day, the earlier they start singing

• The colder the day, the later they start singing Phys.org

Intuitively, one might think, "Well, of course, you wouldn't want to move if it's cold," but the important point is that even among closely related species living in the same wetland, their responses to factors other than temperature were varied. The study reports the following differences for each factor. Phys.org

Humidity

• African yellow warbler: Sings earlier when humidity is high

• Lesser swamp warbler: Sings later

• Little rush warbler: No effect Phys.org

Wind

• Lesser swamp warbler/Little rush warbler: Sings earlier when the wind is strong

• African yellow warbler: No effect Phys.org

Rain

• African yellow warbler/Little rush warbler: Starts later on rainy days

• Lesser swamp warbler: Sings earlier on rainy days Phys.org

Moon (bright nights, near full moon)

• Lesser swamp warbler/Little rush warbler: Starts later the morning after a bright night

• African yellow warbler: No effect from lunar phases Phys.org

Additionally, there was a tendency for singing to start earlier in the middle of the breeding season and later towards the end of the season. Phys.org

With all this information, it becomes clear that the dawn chorus is not a "sunrise = simultaneous start" event but rather an **event whose "start time is adjusted by weather and moonlight."**

Why Does It Matter?—"Sound" as a Conservation Sensor

The value of this research goes beyond just adding to bird trivia. The article explains that mountain wetlands could serve as **"early warning systems"** susceptible to climate change. With research findings indicating that wetlands are shrinking due to global warming, there is a risk that the creatures living there may locally disappear. Therefore, tracking changes in birds' singing start times could provide clues to detect environmental changes. Phys.org

Moreover, the advantages of tracking through sound are significant.

• Even in places difficult for humans to access, recording devices can continuously monitor

• Not only species presence but also "behavioral changes" (delayed singing start/increased silence) can be captured

• When combined with weather data, it can lead to models predicting **"whether they should sing today or not."** Phys.org

The article likens this to a "weather app for birds." If behaviors such as singing, breeding, or staying quiet can be predicted based on temperature, wind, and moonlight, it could also aid in prioritizing conservation efforts. Phys.org

This content has also been reported in an academic paper under the theme "Too Cold to Sing." Taylor & Francis Online

Reactions on Social Media (Current Observations + "Typical Reactions")

As a fact, on the Phys.org display, this page currently shows 0 comments, and the number of shares is also very low (possibly due to being newly published). Phys.org

On the other hand, in an X post by The Conversation Africa, it was introduced with the gist that "birds don't sing randomly; weather and moonlight predict 'singing/silence'," highlighting the interest of the research. X (formerly Twitter)

When such articles spread on social media, the reactions that tend to appear, tailored to the content, are as follows (※Below is a summary