Friday, January 27, 2023

Esther Sebastian: “We are going to a silent waterfall with almost no sound”

Ornithologist Esther Sebastian has done much of her research into bioacoustics in Hawaii. In the image, on the caldera of Mauna Loa volcano.jomar barbosa

Esther Sebastian (Alicante, 41) was inspired to learn the story of Alala, a crow native to the Hawaiian Islands. It became extinct in the wild decades ago and survives only in breeding centers from where they seek to reintroduce it into the wild. But Alala has forgotten how to sing and can no longer warn her relatives that a predator is coming. Everyone he left died. Sebastian, now a researcher with a Ramon y Cajal grant at the Department of Ecology of the University of Alicante, has received the Francisco Bernice Prize, awarded by BirdLife, the Spanish ornithological society (SEO), at its annual congress held in November. Ornithologists use bird sounds as a window into the biodiversity of birds. And he doesn’t like what he hears: a bird with an increasing number of dialects because its habitat is fragmenting, three different species that sing more and more alike because there is hardly any plot left, and in forests A global trend towards silence.

Ask. Almost all animals produce sound and except in the case of whales and some other species, we do not call any of them singing. Why does the song of birds sound like music to us?

answer. Actually, when we study the songs of birds, it is called vocalization. And within vocalizations we have songs and calls. These are the little sounds they use to communicate something. The calls are passed genetically from parent to offspring. The songs are very elaborate and learned. They are not transmitted genetically, but children learn from their parents or from other individuals of their species.

P. But why do we find them enjoyable? Do they have a base, a musical structure?

R. There are bird songs that can be written in musical notes. Obviously, they have a melody, they follow a rhythm. Most of the songs are meant to attract the female. The more beautiful they are, the more likely she is to be attracted to that man and accepted as a mate. To please and attract a woman is a need, a quest. That’s why they have that musicality.

“Most songs are meant to attract a woman. The prettier she is, the more likely she is to be attracted to him.”

P. Do they only sing to attract females? I mean, why do they sing in general, and not just what we consider to be music?

R. They sing or chant for many things. For example, to warn that there is a predator. Territorial species emit alarm signals to defend their territory. They also do this to exchange information between individuals of the same species. Chicks do this for begging. When attacked, they make characteristic sounds. Like humans, they also transmit many types of information.

P. 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 cites in one of his books that the process of learning and the transmission of information through songs may be an analogue of evolutionary processes. The way song is transmitted, which children learn from their parents, but also from other members of the population, would be a process consistent with genetics. If two populations start to change too much, enough to diverge genetically, they can give rise to different species. Similarly, if a species begins to differentiate its songs too much, there may come a time when individuals of the same species cannot recognize each other because they already sing so differently.

The Picture Is Of A Landscape Of French Island In Australia.  The Bottom Graph Is A Sonogram In Which Sounds Were Recorded Over 24 Hours.  It Is An Acoustic Landscape Full Of Life.
The picture is of a landscape of French Island in Australia. The bottom graph is a sonogram in which sounds were recorded over 24 hours. It is an acoustic landscape full of life.Elizabeth Znaidersik and David M. Watson / Universidad Charles Sturt

P. And have you observed this process?

R. This is a process called ring speciation. For example, this was observed in Tibet, where one species began to change its song as it colonized the Himalayan mountains. The population dispersed on both sides and when they met again on the other side, their songs were so different that they could not recognize each other.

P, Some researchers have observed that due to the decrease in the population of birds, the fields and forests are becoming quieter…

R. The loss of species is a process of loss of individuals. But, at the same time, since vocalization has a communicative function, if I don’t have anyone to communicate with, I vocalize less. If I have to defend my territory and I have none, I will speak less. If there are no other individuals of my population around me, I will not try to communicate with them because there are none. It is a process well ahead of the loss of species. Processes that act as predictors of species loss are looked at. Rachel Carson has a book called silent spring which tells us about it. When I was young I used to walk and hear more birds in the field and now I find I hear less. But unless you look at it with data, when you take a recording from the past of what’s called an acoustic landscape and compare it to the present, you don’t confirm it. There are many works that have compared the acoustic space with the present and yes, we are moving towards that silent spring of the book with almost no sound.

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

R. Acoustic space is a resource that is limited, that has to be shared between 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 by how full it is over 24 hours and at different frequencies, we can get an idea of ​​how much diversity there is in that space, so acoustic diversity is a reflection of taxonomic diversity.

The Acoustic Landscape Empties After A Fire.  In The Picture, An Area Of ​​Barmah National Park, Australia.
The acoustic landscape empties after a fire. In the picture, an area of ​​Barmah National Park, Australia.Elizabeth Znaidersik and David M. Watson

P. In a presentation at the SEO Congress, he told the story of some birds from whom there was no one to learn the song.

R. It’s a beautiful story and a little sad too. On the island of Kawai in Hawaii, there are three species of passerine birds, akeki, amakihi and anianiau, all three native to the island. In the last 20 years they have reduced their distribution range by 90%. Previously, naturalists in the field knew which species it was when they heard them sing. But today, until they see the singer, they do not recognize him. We were fortunate that we had recordings of the three species from the 1970s, the beginning of this century and 2018 and were able to compare them. We noticed that vowels were easier to pronounce now than they were 50 years ago, but they were also more similar to each other. Imagine that you are a bird and there are no other individuals of your species around you, but you have other species that sing in a similar way. So, in addition to learning from your own species, you also learn from others. They do not have individuals of their own species to learn from and learn from whomever they can.

P. Is this an isolated case or an example of a global phenomenon?

R. This is the first time that something like this has been demonstrated. Data from the 1970s is not easy to obtain. That’s the problem, we don’t have recordings from 50 years ago to compare. So ours is the only empirical evidence that I know of. What happens in other places? I am sure that if there are birds that have reduced their population, with almost no individuals of their species, they will learn the songs of other individuals of other species. They must be vocal in order to communicate.

P. Several works have looked at differences between populations of the same species but living in the city or the countryside. Are their songs different too?

R. Yes, they change in vocalization. All anyone wants is for their message to go through. And in a city there are many sounds in the environment, there are cars passing by, people talking, there is a lot of noise in the background. The birds try to adapt their songs to that noise. Some change the frequency at which they sing. Others start singing before the noise starts. An interesting work by the Spanish researcher, Diego Gil, studied what time birds start singing near Barajas Airport and in the nearby forest. They found that people at the airport did it early in the morning to try to avoid the rush for planes.

P. One of his discoveries while in Hawaii focused on a bird that had forgotten how it sang…

R. This is also a very sad story. It’s called Alala, it’s the Hawaiian crow. These are very intelligent birds. The population began to decline since the beginning of the last century. In the seventies only 76 individuals were left in the natural environment. They were captured and placed in a captive breeding center. They tried to reintroduce it twice in the mid-1990s and again between 2017 and 2019, and both were unsuccessful. He died free. many, because they were eaten by another native bird, lo, an eagle [el busardo hawaiano], Our task was to compare the calls of this crow with recordings from when it was in the wild, currently 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 as they are not going to be attacked, nor a territorial call as they already have their own territory, the aviary itself. With this data, they want to show them pictures and even models of Io and what kind of sounds it emits to inform others. The idea is to make a third reintroduction attempt. That is the purpose of keeping them in captivity, to see them free again.

P. In Hawaii he also found the opposite end, birds that have built their own Tower of Babel because of the fragmentation of their habitat.

R. There are areas in Hawaii called kipukas. These are patches of forest surrounded by solidified lava. In one of them we heard a bird named Apapan with a very distinctive song. We only saw him there and we heard him whenever we went. But on going to another kipuka, less than a kilometer away, the same sound was not heard. We began to wonder whether this bird had dialects and recorded it on various kipuks. I manually sing all the individual syllables of this species. I counted about 200. Generally speaking, dialects are widespread. They are 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 much smaller scale, eight kilometers from north to south. We think that the process that occurs is called conformity in behavioral ecology. It’s like when you go to Andalusia and the Andalusian accent hits you. This would be a similar process in which birds, when they visit one of these habitat pieces, hear syllables spoken at that location and are able to learn and repeat them. Like I go to some place and try to repeat the syllables of that place to integrate myself.

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