What makes mountain birds sing at dawn – and why are they sometimes quiet? Ecologists explain

Bloemfontein (South Africa), Jan 4 (The Conversation) What makes mountain birds sing at dawn – and why are they sometimes quiet? Ecologists explain Three species of the melodic African warbler bird refuse to get up early and sing their customary daybreak songs when the weather is cold. This new discovery was made recently by a team of soundscape ecologists in South Africa’s mountainous Golden Gate Highlands National Park.

The team’s research co-leader, Mosikidi Toka, studies how animals and the environment make and use sounds, especially in mountains, and is currently completing a PhD on the sounds of natural habitats. He deployed automated audio recorders to record the birdsong and find out how the birds were affected by freezing temperatures.

Which birds woke up the wetlands every morning in your study? ------------------------------------------------------------------- We studied three closely related songbirds. One was the little rush warbler (Bradypterus baboecala). This distinctly brown warbler with pale upper parts is usually spotted sneaking through thick swamp vegetation such as reeds in wetlands.

The second bird was the African yellow warbler (Iduna natalensis), a brown bird with yellow underparts and a yellow rump that lives in wetlands.

The third was the lesser swamp warbler (Acrocephalus gracilirostris). Normally seen swinging on tall reeds, this bird is noticeable for its warm brown body with snowy white underparts.

These small, insect-eating songbirds are widespread across southern Africa, including mountain wetlands. They can also be seen in ponds and artificial dams with tall reeds in residential areas.

All three species actively contribute to the dawn chorus during the breeding season.

We chose to study the warblers in the Golden Gate Highlands National Park because, as a high-elevation park in South Africa and part of the Drakensberg mountain range, which borders South Africa and Lesotho, it has some of the coldest winters in southern Africa.

What is the dawn chorus? --------------------------- Many bird species take part in a dawn chorus. This is when the community of songbirds in a particular habitat sing intensively around sunrise, primarily before and shortly after dawn.

In the southern hemisphere, these choruses typically occur from September to February. Birds sing nearly every day for many reasons, but they sing loudest and most often at dawn during breeding season to attract mates.

Outside the breeding season, they may sing to defend territory or stay in touch with others. During the dawn chorus, males do most of the singing to impress females, who often sing or call back in response.

The song intensity is highest before sunrise and gradually declines as the morning progresses. The birds taking part in the chorus all try to stand out, not blend in. This means they sing at specific times or frequencies. If each species has a different niche, it has a better chance of surviving instead of failing in a competition for “airtime”.

To humans it might sound like a bit of a cacophony, but to the “real” audience (the females of the bird species), it is highly attractive. It’s an important way for them to find the right mate among all those gentleman singers.

What exactly were you trying to find out? ------------------------------------------- We wanted to see how things like temperature, humidity, wind, rain, and the moon affect birds singing at dawn in a high mountain wetland.

Knowing this helps scientists keep a closer eye on mountain wildlife and adjust conservation efforts as the climate changes. These wetlands are like early warning systems: studies show that warming is already shrinking them, putting many plants and animals at risk of disappearing locally.

To understand how weather – like cold, wind, humidity, or rain – affects birds singing at dawn, we focused on species that are closely related. If we compared very different birds, any changes in their singing would probably come from their body differences, not from the weather itself.

We used special audio recorders that could capture bird songs over long distances and for long periods without us being there. These recorders picked up all the singing from the start to the end of the dawn chorus.

To find the songs of the birds we were studying, we used a computer program called Kaleidoscope Pro, which can pick out specific bird calls from a huge mix of sounds.

We tracked each bird’s songs to see when they started singing and how often they sang each day. At the same time, we recorded daily weather data (temperature, humidity, wind and rain) from a nearby weather station, and we got moon phase information from online records.

We then used a mathematical approach to see how weather affected when our birds started singing each morning – similar to figuring out what makes the rooster crow at sunrise.

What were your findings? --------------------------- Our study found that all three warbler species began singing earlier on warmer days and later on colder days, which was expected because these birds are adapted to stay in this area.

Apart from temperature, we found that environmental factors influenced the daily start of the dawn chorus differently among the species.

Humidity: Higher humidity led to the African yellow warbler calling earlier, while the lesser swamp warbler started calling later. The little rush warbler’s singing times were not affected by humidity.

Wind: The lesser swamp warbler and little rush warbler started singing earlier on windier days, but wind had no effect on the African yellow warbler.

Rainfall: This delayed the start of the dawn chorus for the African yellow warbler and the little rush warbler. However on rainy days, the lesser swamp warbler woke up earlier to sing.

The moon: After brighter nights, around full moon, the lesser swamp warbler and little rush warbler started singing later the next morning while the African yellow warbler was not affected at all by the phases of the moon.

For all species, singing began earliest in the mid-breeding season and latest towards the end of the season.

Why is this research valuable? --------------------------------- This study helps scientists see how weather and moonlight affect birds living in high mountain wetlands. Think of it like a weather app, but for birds: using temperature, wind and moonlight, these models can predict when birds will sing, breed or stay quiet, helping conservationists protect them more effectively.

Knowing more about the three warblers improves our understanding of how species adapt to harsh environments under changing climates.

Our study also reveals how everyday weather influences wildlife. It shows that wetland ecosystems and songbirds are very vulnerable to environmental change, especially with increasing human activities in protected areas such as the Golden Gate Highlands National Park.

We believe this research also shows the value of soundscapes – the sounds of nature – not only for our enjoyment, but for understanding how the ecosystem works and can be conserved. (The Conversation) RD RD