Rinjani scops owl

The new species on Lombok - the Rinjani scops owl (Otus jolandae). Credit: Philippe Verbelen

A new species of owl called the Rinjani scops owl has been discovered, and it’s unique to the tiny Indonesian island of Lombok.

Until fairly recently, it was common practice for scientists to identify owl species based largely on their plumage and morphology. Both features are important in distinguishing all kinds of birds, but can be unreliable, as owls often change their colouring to better blend in with their environment. The same species of spocs owl living in different geographic regions can have noticeably different plumage colours and patterns, which had led to what Smithsonian ornithologist Joe T Marshall referred to in 1978 as “several embarrassing misalignments”.

Marshall had been sent to Thailand in the late ‘70s to fix up some messy taxonomy of its endemic owls, and it was here that he became the first researcher to propose that vocalisations were a more reliable identifier of scops owl species than variations in morphology and plumage. Using this new technique, he went on to completely revise the classification of the scops owl genus Otus.

plumage for species comparisons

A 1964 illustration of the sandy scops owl (Otus icterorhynchus) from Allen Phillips and Joe Marshall's 'The Birds of Arizona'. According to Marshall, the absence of wings emphasises the important parts of the plumage for species comparisons. Credit: Joe T Marshall

Since then, recordings of owl vocalisations have become a big part of identifying owl species, and this is how George Sangster from the Department of Vertebrate Zoology at the Swedish Museum of Natural History and Ben King from the Ornithology Department at the American Museum of Natural History discovered the Rinjani scops owl of Lombok, and named it after Indonesia's second highest volcano, Gunung Rinjani.

Lombok is located in the West Nusa Tenggara province of Indonesia, about 25 km from Bali to the west and 15 km from Sumbawa to the east. It has an area of 4,725 km and a population of 3.16 million, and its famous Gunung Rinjani National Park is home to porcupines, long-tailed macaques, civets and the endangered Javan rusa deer.

A pure coincidence saw both Sangster and King travel to Lombok in 2003 to record and study the vocalisations of a local population of nightjars to identify whether they belonged to a potentially new species that occurs on the neighbouring islands of Flores and Sumba, or to the large-tailed nightjar species (Caprimulgus macrurus) with which it had long been associated. It turns out this was a population of large-tailed nightjars, but while they were there, Sangster and King picked up on some owl vocalisations they had never heard before.

“On the very first night, just a few hours after my wife and I arrived on Lombok, we heard the vocalisations of an owl that we were not familiar with,” says Sangster. “Initially we weren't sure whether it was perhaps a previously known species from Java and Bali that for some reason had been overlooked on Lombok. That was quickly ruled out when we played it back our sound recordings of the owl. The owls responded strongly to this and approached us so we could get a nice view. They looked nothing like the owls on Java and Bali.”

“I arrived on Lombok three days after George for the purpose of getting tape recordings of the same species of nightjar George wanted to record and for the same reason,” says King. “At the time, George and I had not met and did not know each other, although we knew of one another. My experience was similar to George's. While I was recording the nightjar, I heard a song that sounded like an owl, but unlike any I'd heard in years of fieldwork in Indonesia. I recorded the owl and played the tape back to the owl and eventually I got a good view of a pair.”

Rinjani Scops Owl

Rinjani scops owl. Credit: Phillipe Verbelen

There are 51 known species of scops owls, making their genus the largest in the ‘true owls’ family Strigidae. Scops owls are characterised by their small, erect ear tufts, relatively compact bodies and plumage the colour of dusty bark and dried-out leaves. The other family of owls is the Tytonidae family of barn owls, with ears hidden on the side of their heads and placed asymmetrically for an enhanced detection of sound position and distance when they’re hunting, and a more distinct facial mask. They could also quite possibly be some kind of witch.

The Moluccan scops owl (Otus magicus), which stands around 24 cm tall, is common species on the Indonesian islands, and was thought to occur in various parts of Lombok. It looks so similar to the new Rinjani scops owl that over the last 100 years, no one had bothered to confirm this via vocalisation recordings or DNA comparisons. “Prior to my Lombok visit, I had not thought of tape-recording the scops owl there, as it looked like the Moluccan scops owl, and I just assumed that the earlier researchers were correct in their assessment,” says King.

“However,” adds Sangster, “its whistle sounded completely different from the Raven-like croak of [the Moluccan scops owl]. Now things got interesting: we might have a different species. However, we fully expected that some taxonomist already had given a name to this population, and we did not realise at the time we had discovered an entirely new species. That came later, at home when we checked the taxonomic literature and examined our recordings more closely.”

map of Wallacea

Map of Wallacea, a group of Indonesian islands separated by deep water straits from the Asian and Australian continental shelves, showing approximate rages of owl species and subspecies. Credit: Sangster, King et. al.

Over the past decade, Sangster and King have been putting together a case for their Lombok spocs owl, which they have called Otus jolandae after Sangster’s wife, as being a unique species. This involved collecting recordings from different parts of the island, investigating whether or not the owl was located on other Indonesian islands, and comparing the Rinjani scops owl to all other relevant species in museums. Finally, a DNA analysis of the Rinjani scops owl and those other species provided the confirmation the researchers needed.

“Only when we had tied up all loose ends were we comfortable announcing our new species,” says Sangster. “Owl vocalisations can be highly informative for taxonomists. They most likely have a genetic basis, are relatively easy to study, and are being used by the birds themselves to distinguish species. However … one needs to respect the same scientific principles that apply to other types of data. You must have multiple recordings, study geographic variation, perform statistical analyses, and make sure that the right comparisons are made (to avoid the 'apples-and-oranges' problem). In addition, most owls have very simple vocalisations, and there is no reason to expect that all species have completely unique songs. Therefore, it is always a good idea to study other types of data as well, including DNA.”

Sangster and King have published their discovery in today’s issue of PLoS One. “Although it took us almost 10 years to describe the new owl, this is hardly exceptional,” says Sangster. “Of course, all the easy ones have been described a long time ago, so those bird species that remain undiscovered will not easily give up their true identity.”

What isn’t clear just yet is how this owl has remained Lombok’s only endemic species, when the island of Sumbawa is just 15 km away – an easy distance for an owl to fly. Sangster has a theory that because the smaller islands in the Indonesian archipelago only harbour one species of scops owl each, some kind of competitive exclusion could be at play. “This is speculative,” he adds, “and in fact more fieldwork is necessary to know for sure that the Rinjani scops owl does not occur in extreme western Sumbawa.”

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