Analysis of recordings of owls’ screeches and DNA from a museum specimen that is over 173 years old informs new species.
Scientists have been studying screech owls for decades and while they are considered a well-understood group, their nocturnal nature does not make it easy to tell them apart by plumage and size alone. In a new paper in Zootaxa, researchers described two new species of screech owl using multiple voice recordings, DNA sequencing and antique data from a museum specimen that is over 173 years old.
The flash of a camera offers a clearer picture well beyond what the human eye can see at night. Audio recordings of varying screeches belonging to an assortment of birds, paired with DNA sequencing provides additional assurances of a much greater genetic variability and diversity among populations of different owl species, than was previously known.
While the Xingu (Megascops stangiae) and Alagoas (Megascops alagoensis) screech owls are new to science, they’re already in danger of disappearing forever.
“Both new species are threatened by deforestation, one is already critically endangered,” said Jason Weckstein, PhD, associate curator of Ornithology in the Academy of Natural Sciences and an associate professor in Drexel’s College of Arts and Sciences.
“The Xingu Screech Owl is endemic to the south side of the Amazon river in a region known for its infamous arc of deforestation, and the Alagoas Screech Owl is found in a few remaining fragments of isolated Atlantic Forest in northeastern Brazil. Both of these regions are increasingly fragmented and there needs to be big uniform patches of green conserved in both of these regions if we want these species to succeed,” explains Weckstein.
Weckstein, who is a coauthor on this study, worked with Therese A. Catanach, PhD, a post-doctoral researcher in the Ornithology Department of the Academy of Natural Sciences, to successfully extract and sequence DNA from a specimen in the Academy’s collection that is over 173 years old, a lectotype for the Tawny-bellied Screech Owl, which serves as an icon for the species. This antique genetic data was critical for two reasons.
DNA sequence data, particularly data from a lectotype, was critical for diagnosing the differences among the various populations of owl in these regions because the plumage coloration is so cryptic among them. A lectotype serves as a type specimen upon which the description and name of a new species is based. In this case this bird was from the north bank of the Amazon River and therefore this population is now called the Tawny-bellied Screech Owl (Megascops watsonii), which we now know is genetically different from the birds on the south bank of the river, the Xingu Screech Owl. “The birds on the on the north bank of the Amazon, are not the same as those on the south bank and they do not fly across the river,” explains Weckstein.
The Academy’s lectotype was designated as a type specimen for Megascops watsonii. A type specimen is kind of like an icon for its species – meaning that this exact specimen or series of specimens was used in the formal published scientific description of the species and the name Megascops watsonii is therefore formally attached to these specimens. According to zoological taxonomy rules, if you want to describe something new you have to compare it to a type specimen and in this case the researchers were able to compare the DNA of the type with DNA from other specimens in their study.
“We were using multiple owl voice recordings and DNA data for this study – but of course the antique specimen had no voice recording, so successfully sequencing intact fragments of DNA informed us that this type specimen for Megascops watsonii matched the groups of birds with a particular vocalization from the north bank of the Amazon and therefore that meant that the genetically unique south bank birds were unnamed,” said Weckstein.
Having DNA sequences from a type specimen of Megascops watsonii gave researchers a valuable clue to apply to their science. The DNA from the over 173-year-old owl effectively illuminated these new species.
The newly discovered screech owls are cousins of the Eastern Screech Owl that is common in the United States. Until this study, the new species were lumped together with the Tawny-bellied Screech Owl and the Black-capped Screech Owl, which are found in two specific biomes, South Americas’ Amazonian and Atlantic Forest.
“A lot more work like this needs to be done,” says Weckstein. “This has an impact on our understanding of the planet and where we need to be targeting our conservation efforts while helping us unlock what the true biodiversity is out there.”
For example, in southeastern Amazonia where the new Xingu Screech Owl is found, the Brazil soy trade is linked to widespread deforestation. Deforestation in the region involves both cutting and burning of the forest to make way for soybean farming and coupled with the unprecedented 2019 fires, makes for extensive forest fragmentation and troubling future for these owls.
“Not even professional ornithologists who have worked on owls for their entire lives would agree about the actual number of species found in this group, so a study like ours has been awaited for a really long time,” says Alex Aleixo, PhD, head of the research team responsible for the study, and currently curator of birds at the Finnish Museum of Natural History in the University of Helsinki, Finland.
Altogether, 252 specimens, 83 tape-recordings, and 49 genetic samples from across the range of the Tawny-bellied Screech Owl complex in South America were analyzed. A significant number of specimens were collected by the research team itself, especially the study’s lead author Sidnei Dantas, PhD, who spent a good share of his time in graduate school searching for and tape-recording screech owls in South American rainforests. In addition, natural history collections and their materials collected over the centuries were essential to complete the study´s unprecedented sampling.
The owls that the researchers were looking for live in the trees, often a hundred feet above the forest floor. That makes studying them difficult. But the researchers had a secret weapon: the screech owls’ namesake screech.
“To draw the birds out, we used tape recordings,” explains John Bates, PhD, curator of birds at the Field Museum in Chicago and one of the study’s authors. “We’d record their calls and then play them back. The owls are territorial, and when they heard the recordings, they came out to defend their territory.”
Teasing out the differences between the species started with years of fieldwork in the Amazon rainforest, as well as the Atlantic forest running along the eastern part of Brazil and surrounding countries. Bates, who usually conducts fieldwork during the day, says that doing fieldwork in the rainforest at night comes with new challenges. “For me it’s more a feeling of fascination than being scared, but at the same time, you’re running into spider webs. If you’re wearing a headlight you see the eyeshine of the nocturnal animals. One time I was stepping over a log and I looked down and there was a tarantula the size of my hand just sitting there,” says Bates. “If I had been a kid I would have been scared to death.”
The scientists compared the birds’ calls and found that there were variations in the sounds they made, indicative of different species. They also examined the birds’ physical appearances and took tissue samples so they could study the owls’ DNA at the Field Museum’s Pritzker DNA Lab.
“The study would not have been possible if it were not for the great biological collections in Brazil and USA which I visited during my work, and that sent us essential material, either genetic or morphological. This highlights the importance of such research institutions for the progress of science and hence of the countries they represent,” says Dantas, who conducted the study as part of his PhD dissertation at the Goeldi Museum in Belém and is currently working as a nature guide in Brazilian Amazonia.
The combination of genetic variation, physical differences and unique vocalizations led the team to describe the two new species, in addition to the previously known Tawny-bellied Screech Owl: the Xingu Screech Owl and the Alagoas Screech Owl. The Xingu Screech Owl’s scientific name is in honor of Sister Dorothy May Stang, an activist who worked with Brazilian farmers to develop sustainable practices and fight for their land rights; its common name is for the area where the owl is found near the Xingu River. The Alagoas Screech Owl’s name is a reference to the northeastern Brazilian state of Alagoas where the owl is primarily found.
Researchers at the Academy of Natural Sciences of Drexel University, the Museu Parasense Emilío Goeldi in Belém Brazil, The Finish Museum of Natural History, and the Field Museum of Natural History collaborated on this work.
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