Scientists discover hummingbird in the Atlantic Forest that sings at an ultrasonic frequency

A species of hummingbird with an ultrasonic song has intrigued scientists since 2015. This is because the type of high-pitched vocalization above the audible limit for us humans is even common for other mammals, such as bats and cetaceans (whales and dolphins), but it is rare in birds.

But a Brazilian hummingbird is unique in presenting this type of sound frequency, and the suspicion is that it uses it precisely to escape the symphonic competition of other birds.

The discovery, led by Brazilian neuroscientist and professor at the Oregon School of Medicine (USA), Cláudio Mello, has the participation of researchers from the University of Arizona and Rockefeller University, both also American, and from the Pontifical Catholic University of Belo Horizonte (PUC). -BH) and the Federal University of Minas Gerais (UFMG).

White-tailed black hummingbird call (Florisuga fusca), the bird, endemic to the Atlantic Forest, is capable of both producing sounds and hearing them above 10 Hertz frequency (considered high).

To give you an idea, most birds sing within the intermediate sound frequency, from 0.5 to 6 Hz, with an average of 2 to 3 Hz. Already the individuals of Florisuga studied sang at an average frequency of 11.8 Hz.

The first observations of the species’ vocalization were made in the 1970s, in the reserve area of ​​the Instituto Nacional da Mata Atlântica (INMA), in Santa Teresa (ES), by the park’s founder, naturalist Augusto Ruschi.

At the time, suffering from hearing loss, the scientist described that the hummingbird “sang, but he couldn’t hear”, thinking it was his own condition. Little did he know that, in reality, it was not possible to hear the bird’s song.

The description of the sound frequency, however, was completed in 2018, in a publication in the scientific journal Current Biology. Since then, Mello says that he received a grant from the National Geographic Society to make a new expedition to Brazil in early 2020, but, with Covid, the fieldwork was postponed.

After the most restrictive period of the pandemic, he and his colleagues were able to carry out a study in loco last October. They observed 40 birds and saw that the ultrasonic frequency was, in fact, unique for this species of hummingbird.

“When we came back with specialized equipment to capture ultrasound, we confirmed what we had already seen, that they sing in a range that other birds generally won’t hear. And that can be interesting, they can occupy a range where their communication is not interrupted”, describes Mello.

According to him, the higher frequency, however, travels in shorter waves, which would indicate a short distance communication. “We are now analyzing the collected data to obtain the answer of how far away this information [o canto] arrives, and also whether the chicks can hear their parents.”

In birds, vocalization is an important instrument even for the learning of chicks. “Vocal learning implies that the chick from inside the nest hears the adult’s song and imitates the song, so it’s extremely important to understand if they can hear the parents.”

As there is little data in the literature even on how the learning behavior in hummingbirds works, the research will still have to be tested, including playing the recorder in other locations where the species is found, to find out if this teaching is passed between the generations.

According to the scientist, a next step in the research is to study the internal anatomy of Florisuga to evaluate the adaptations that may exist in the vocal cords and inner ear of these animals.

“Now we are going to focus on long-term projects. We are waiting to establish a partnership with INMA to study the ecology of this species, which is really unique. This is a good example of how little we know about biodiversity, and especially about the forest. Atlantic,” he says.

The expectation is that it will not be too late, since the Atlantic Forest is the Brazilian biome that lost the most area in the last 40 years. Scientists have already proven the importance of the forest, which is considered a “hotspot” of world biodiversity, for understanding the diversity of Brazilian species and also for discovering new plants and beings with pharmacological and economic potential.

As the equipment used is also suitable for studying bats, the neuroscientist says that partnerships of this type are also welcome, even considering the high cost of each device, of up to R$ 10,000 for the ultrasonic sensor and R$ 15 thousand to R$ 20 thousand for the recorder. “The hummingbirds sing until about five or six in the afternoon, and then the bats come, so you can do two surveys in the same day.”