Principe, a small island off Africa's western coast, is home to strange screeches that haunt the night.

Few people have heard the noises coming from the old-growth forests on the island's southern, uninhabited tip. They begin shortly after sunset and sometimes sound like an insect's rasp, a cat's mewling, or a monkey's call. Locals first noticed the squawks in 1928, but without the ability to remain a mystery.

The raptor, officially known as the Principe scops-owl, or Otus bikegila, is one of 59 species of scops-owls. Scientists know little about the nocturnal O. bikegila, including what it eats, how it hunts, and the meanings of its unusual sounds.

"This is an integrative study because it's kind of like a puzzle," says study co-author Bárbara Freitas, an evolutionary biologist at Madrid's National Museum of Natural Sciences.

"We have multiple pieces, such as the owl's vocalisations, morphology, and genetics, and then we can put all the data together and see if it was truly new," says Freitas, a National Geographic Explorer.

While the newly described species is thought to have between a thousand and 1,500 individuals, scientists believe the owl's entire range is only about five square miles within Principe Obô Natural Park.

"We believe it completely depends on that native forest," Freitas says. "It's already a protected area, but it's so easily damaged." (Learn about the world's most giant owl, a critically endangered species.)

According to Freitas, a small hydroelectric dam is currently planned to be built nearby, which could lead to deforestation in the area.

For these reasons, scientists recommend that the International Union for Conservation of Nature grant the owl critically endangered status in a new study published in the journal Bird Conservation International.

Former parrot catcher on the prowl

Never have been discovered and described if it hadn't been Bikegila as everyone knows him.

Long before the establishment of Principe Obô Natural Park in 2006, Bikegila—whose nickname has no particular origin—was one of many men who made a living by climbing into the canopy and stealing African grey parrot chicks from their nests and selling them as pets.

Bikegila turned his extensive knowledge of the landscape toward another purpose after the area was protected and parrot harvesting was prohibited. In fact, Bikegila was among the first to spot the owl while looking for parrot chicks in the early 1990s.

He has accompanied scientists on every expedition to find the owl for nearly a quarter-century, including the trip that resulted in the first photographic evidence of the species in July 2016. Then, on May 29, 2017, Bikegila and Hugo Pereira of the Portugal's University of Porto, another study co-author, caught one of the animals for the first time.

Living only in the old-growth forests of Príncipe Island, the tiny bird is likely already critically endangered, experts say https://t.co/x6Xhq0xlai

— National Geographic (@NatGeo) November 1, 2022

Later, specimens were sampled and released to honour the work of local guides around the world.

When asked what he wanted the world to know about his island home, Bikegila flipped the question.

"How come they can't come here?" "You should invite them," Bikegila, who speaks Portuguese, told National Geographic through 
the landscape, the birds, and the history for themselves before passing judgement." This is preferable."

Freitas and colleagues have also published a third study in their search for the following new species: A pre-print detailing their method for discovering the owl, which they believe used audio recorders to hear what animals were making noise in the darkness. They then combed through the data for the owl's signature call—a short repeated "you"—often performed in a duet, which the scientists had captured in the wild.

Freitas then created a computer programme to sift through countless hours of audio recordings in order to identify the Principe scops-owl among the din of parrots, insects, and other nightlife. (Learn more about nature's noisemakers here.)

"It's the sound equivalent of camera trapping," says Nigel Collar, an African scops-owl expert at the non-profit BirdLife International who was not involved in the new research. Collar has used acoustic monitoring to survey owls, but not in the way that the new paper describes.

"It's great to see this owl finally described," Collar adds. "They have clearly done an excellent job."

According to Freitas, the best part about passive acoustic monitoring is that scientists can continue to analyse and reanalyze the recordings based on which animals or sounds are of interest. That means the same data could potentially be used to identify even more new species lurking in the shadows.

"It's going to really boost the knowledge we have now," she says.