Esther Sebastián: "We are going towards a silent spring in which there are almost no sounds"

Ornithologist Esther Sebastián has done most of her research in bioacoustics in Hawaii.

In the image, on the caldera of the Mauna Loa volcano. Jomar Barbosa

Esther Sebastián (Alicante, 41 years old) was moved to learn the story of the alala, a crow native to the Hawaiian Islands.

It went extinct decades ago in the wild and only survives in breeding centers from which they want to reintroduce it into the wild.

But the alala has forgotten how to sing and can no longer warn its kindred that a predator is coming.

Everyone they released died.

Sebastián, now a researcher with a Ramón y Cajal grant in the Department of Ecology of the University of Alicante, has received the Francisco Bernis prize awarded by the Spanish Ornithological Society (SEO) Birdlife at its annual congress, held in November.

The ornithologist uses the sounds of the birds as a window into the biodiversity of the birds.

And she doesn't like what she hears: a bird with an increasing number of dialects because its habitat is fragmenting,

Ask.

Almost all animals produce sounds and except in the case of whales and some other species, we call none of them singing.

Why does the song of birds seem like music to us?

Reply.

Actually, when we study the songs of birds, we call it vocalizations.

And within the vocalizations we have the songs and the calls.

These are those short sounds that they use to communicate something.

Calls are passed down genetically, from parent to offspring.

The songs are much more elaborate and are learned.

They are not transmitted genetically, but children learn from their parents or from other individuals of their species.

Q.

But why do we find them nice?

Do they have a base, a musical structure?

A.

There are bird songs that can be transcribed into musical notes.

Obviously, they have a melody, they follow a rhythm.

Most of the songs are to attract the female.

The prettier they are, the more likely she will be attracted to and accept that male as a partner.

There is a need, a search to please and attract the female.

That's why they have that musicality.

“Most of the songs are to attract the female.

The prettier they are, the more likely she is to be attracted to them."

Q.

Do they only sing to attract the female?

I mean, why do they sing in general, not just what we consider music?

R.

They sing or vocalize for many things.

For example, to warn that there is a predator.

Territorial species emit alarm signals to defend their territory.

They also do it to exchange information between individuals of the same species.

Chicks do this to beg for food.

When they are being attacked they emit particular sounds.

Like humans, they also transmit many types of information.

Q.

Did Charles Darwin study the song of birds?

R.

_

He did not go so far as to analyze it directly in his work, but he does cite in one of his books that the learning processes and the transmission of information through songs can be an analogue of evolutionary processes.

The way in which the song is transmitted, which the children learn from their parents, but also from other members of the population, would be a process analogous to genetics.

If two populations start to change a lot, to separate a lot genetically, they can give rise to different species.

Similarly, if a species begins to differentiate its songs a lot, there may come a point where individuals of the same species do not recognize each other because they already sing very differently.

The image is of a landscape of French Island, in Australia.

The lower graph is a sonogram with the sounds recorded in 24 hours.

It's a lively soundscape.Elizabeth Znidersic and David M. Watson/Charles Sturt University

Q.

And have you observed this process?

A.

It is a process called ring speciation.

It was observed, for example, in Tibet, where a species began to change its song as it colonized the Himalayan mountains.

The populations expanded to both sides and when they met again on the other side, their songs were so different that they were unable to recognize each other.

Q.

_

Some researchers have observed that fields and forests are becoming quieter as bird populations dwindle...

R.

There is a process of loss of species, of loss of individuals.

But, also, since vocalizations have a communication function, if I don't have someone to communicate with, then I vocalize less.

If I have to defend my territory and I don't have anyone, I will vocalize less.

If I do not have other individuals from my population nearby, I am not going to try to communicate with them because there is no one.

It is a process that is ahead of the loss of species.

Processes that function as predictors of species loss are seen.

There is a book by Rachel Carson called

who tells us about this.

When she was little I listened and heard more birds in the field and now I think I hear less.

But until you see it with data, when you take recordings from the past of what is called the acoustic landscape and compare it with the current ones, you don't confirm it.

There are several works that have compared the acoustic space years ago with the current one and, yes, we are heading towards that silent spring of the book in which there are almost no sounds.

Q.

What does the acoustic landscape of the environment tell us about the diversity of the forest?

A.

The acoustic space is a resource that is limited, that has to be shared between the species, so they try to adapt to that space.

Sometimes they change the frequency in which they sing or the moment in which they do it.

If we analyze that acoustic space, how full it is throughout the 24 hours and at different frequencies, we can get an idea of ​​what diversity is like in that place, so acoustic diversity is a reflection of taxonomic diversity.

After a fire, the acoustic landscape empties.

In the image, an area of ​​the Barmah National Park, in Australia.Elizabeth Znidersic and David M. Watson

Q.

In the presentation at the SEO congress, you told the story of some birds that had no one to learn to sing from.

R.

It is a very beautiful story and a little sad.

On the island of Kawaii in Hawaii, there are three species of passerine birds, the akeke'e, the amakihi and the anianiau, all three native to the island.

In the last 20 years they have reduced their distribution range by 90%.

Before, naturalists in the area knew what species it was when they heard them sing.

But today, until they see the individual who sings, they are not able to identify him.

We were lucky to have recordings from the 1970s, the beginning of this century and 2018 of the three species and to be able to compare them.

We observed that the vocalizations were simpler now than 50 years ago, but they were also more similar to each other.

Imagine that you are a bird and you do not have other individuals of your species nearby, but you do have other species that sing similarly.

Then,

In addition to learning from your own species, you learn from others.

They do not have individuals of their species to learn from and they learn from whom they can.

Q.

Is it an isolated case or an example of a global phenomenon?

R.

It is the first time that something like this has been demonstrated.

It is not easy to have data from the 1970s.

That's the problem, we don't have recordings from 50 years ago to compare.

So ours is the only empirical proof I know of.

What happens in other places?

I am sure that if there are birds that have reduced their populations, that have almost no individuals of their species, they will learn the song of other individuals of other species.

They need to vocalize to communicate.

Q.

Many works have observed differences between populations of the same species, but living in the city or in the countryside.

Are their songs different too?

R.

Yes, they do change in vocalizations.

What anyone wants is for her message to get through.

And in a city there are many sounds in the environment, there are cars passing by, people talking, a lot of background noise.

The birds try to adapt their songs to that noise.

Some change the frequency at which they sing.

Others start singing earlier, before the noise starts.

An interesting work by a Spanish researcher, Diego Gil, studied what time the birds begin to sing near the Barajas airport and in a nearby forest.

He found that those at the airport did it early in the morning to try to avoid rush hour for planes.

Q.

One of your investigations, while you were in Hawaii, focused on a bird that had forgotten how it sang...

R.

It is also a very sad story.

It's called alala, it's the crow from Hawaii.

They are very intelligent birds.

The population began to decrease since the beginning of the last century.

In the seventies there were only 76 individuals left in the natural environment.

They were captured and placed in a captive breeding center.

They have tried to reintroduce it twice, in the mid-1990s and between 2017 and 2019, and both failed.

They died free.

Many, because they were eaten by another native bird, the Io, a hawk [the Hawaiian buzzard].

Our job was to compare the vocalizations of this crow from recordings we had from when it was in the wild, with the current ones, already in captivity.

They have lost almost all their songs, both alarm and territorial.

They are in an aviary, so they do not need an alarm signal because they are not going to attack them,

not a territorial call because they already have their territory, the aviary itself.

With this data, they want to show them images and even models of Io and what kind of vocalizations to emit to notify others.

The idea is to make a third reintroduction attempt.

That is the objective of having them in captivity, to see them free again.

Q.

In Hawaii they also found the opposite extreme, birds that due to the fragmentation of their habitat have built their own Tower of Babel.

R.

There are areas in Hawaii called kipukas.

These are patches of jungle surrounded by solidified lava.

In one of them, we heard a bird, the apapane, with a very peculiar song.

We only saw him there and whenever we went we heard him.

But when going to another kipuka less than a kilometer away, the same sound was not heard.

We began to wonder if this bird has dialects and we recorded it on several kipukas.

I manually characterized all the different syllables this species sings.

I counted almost 200. Normally, dialects occur on a large scale.

There are them within the same species in populations in eastern and western Europe, or in the north and south of a country, but here it is a very small scale, eight kilometers from north to south.

We think that the process that occurs is what in behavioral ecology is called conformism.

It's the same as when you go to Andalusia and the Andalusian accent hits you.

It would be an analogous process in which birds, when they go to one of these habitat fragments, listen to the syllables that are vocalized in that place and are capable of learning and repeating them.

As if I go to a place and try to repeat the syllables of the place to integrate myself.

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