The study eliminates the hypothesis of the reason why birds sing at dawn: NPR

Researchers have new proofs of what makes birds so much noise early in the morning, and it is not for some of the reasons they thought before.

For decades, a dominant theory on the reasons why birds sing at dawn – called the “dawn choir” – have been that they can be heard further and more clearly at the time.

The sound moves faster in the damp air and it is wet early in the morning. It is less windy too, what is thought To reduce any distortion of their vocalizations.

But scientists from the K. Lisa Yang Center for Conservation Bioacoustics d’Onnithology and the DHVani project in India have combed with bird audio recordings in the tropical forest. They say they did not find any evidence to safeguard this “acoustic transmission hypothesis”.

It was among the hypotheses involving environmental factors. Another is that birds spend their time singing at dawn because there is a weak light and it is a bad time to look for food.

“We have essentially not found a lot of support for some of these environmental clues that have been claimed in literature as hypotheses” to explain why birds sing more at dawn, explains Vijay Ramesh, postdoctoral research partner in Cornell and the main study of the study.

The study, called “Why is the upstream early? An assessment of hypotheses for the avian biases of the dawn»Was published this month in the Peer Reading Committee Journal Philosophical transactions of the Royal Society B.

Researchers have not definitively indicated a reason why the dawn choir East Performs, but they found support for ideas that the racket early in the morning relates to birds marking their territory after being inactive at night and by communicating on food search.

They analyzed the audio recordings of the tropical forest

A large strip of forest covers the mountains of western India, in the district of Wayanad of Kerala. The Western region of Ghat is the place where researchers collected audio.

Kiran / AFP Manjunath via Getty Images

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Kiran / AFP Manjunath via Getty Images

The team analyzed the recordings of the audio recorders placed in 43 locations in the mountain range of Western Ghats in the south of India, known as the Biodiversity Hotspot. They examined the sounds of what they determined were 69 different species of birds. They studied the recording of hours around dawn and hours around twilight to compare the activity.

Not surprisingly to anyone who was awakened by a cacophony of bird calls, the “vast majority” of the species they studied had a “significantly higher” vocal activity at dawn compared to twilight.

In order to assess the acoustic transmission hypothesis, they had to do a prediction first: that birds which vocal at higher frequencies would be more active at dawn than at twilight. They predicted this because they said that the higher frequencies are more likely to degrade due to environmental factors, such as wind and humidity.

But they write that they have found “no significant relationship between the maximum frequency of vocalizations” and a type of preference of the bird to make noise at dawn instead of twilight.

And when the researchers examined another “environmental” factor – that birds sing in the low light of dawn because this weak light has a bad time to eat – it would be logical that the same thing is true to twilight. But most birds were much more vocal at dawn.

“I think it is probably the most important discovery here, is not to demonstrate what the dawn refrain is definitively speaking, but to exclude this class of hypotheses, this open environmental window of hypotheses,” explains Steve Nowicki, biology professor at Duke University who studied birds and was not involved in the study.

What they found implies that birds were marked their territory and pursue “hunting festivals”

A white throat martin is represented in the state of Rajasthan in India in 2013. The bird was among those studied which were the most vocal at dawn instead of twilight.

Sébastien Berger / AFP via Getty Images

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Sébastien Berger / AFP via Getty Images

The relations they exercised were that the more territorial and those who have an omnivorous regime were more vocal at dawn rather than twilight.

Birds that are very territorial “tend to make advertisements early in the morning for claiming or advertising territories where they are” after a night of inactivity, says Ramesh.

And with regard to food, birds engage in “a lot of communication on the place where the resources are, or often if there is a nearby predator,” he said. They speculate that a reason why omnivorous birds have a slightly higher level of vocal activity at dawn is because they often participate in “hunting parts” of the herd which occur more often at dawn. But on the reasons why these hunting parties occur at dawn to start, they are not safe.

As researchers note, there are a lot of warnings. They only studied birds in a particular tropical region in India (Ramesh says that there is “almost no overlap” with the bird species that we see in the United States). They did not observe the birds visually and did not record exactly when dawn and twilight started, they just used approximate times.

Many hypotheses exist for the chorus of the dawn. Nowicki says that the researchers here did not examine others, including the birds sing in the morning to warm up, “as an interpreter making vocal warming”, or that he is linked to women coupling early in the morning.

In the article, scientists noted future research opportunities using audio equipment and more sophisticated climate monitoring.

“Sometimes there are phenomena, as the chorus of the dawn could be one, where there is not a single causal reason. And it is a bit frustrating for scientists,” adds Nowicki.

There could be “different reasons that species are more likely to sing at dawn or not,” he said. “In a way, it is an unsatisfactory answer because it is not to button things.”