By Chiti Arvind, 29th June 2022
When a search for over a decade yields no clues, how does one detect a species shrouded in mystery? The name Jerdon’s courser, scientifically known as Rhinoptilus bitorquatus, often piques people’s interest, leading to enthusiastic discussions on how to find this elusive bird. It was first discovered in India’s Eastern Ghats mountains in the mid 1800s by Sir Thomas C. Jerdon, a British surgeon and naturalist, after whom several plants and animals have been named. What is so flummoxing is that after 1900, the bird was not seen for 86 years until Bharat Bushan and his team rediscovered it in 2008. Extensive research was subsequently carried out by P. Jeganathan, who was also the last person to see it, in 2008. For the past 14 years, however, this bird’s presence has remained a mystery. Jerdon’s courser is categorized as Critically Endangered on the IUCN Red List and is a Schedule I species under the Indian Wildlife Protection Act (1972).
Jerdon’s courser is endemic to a small region of open forest scrubland in the Sri Lankamalleshwara Wildlife Sanctuary in the foothills of the Eastern Ghats of Andhra Pradesh, India. Little is known about this species’ life history and behaviour. Previous attempts to discover it involved setting up camera traps, conducting manual searches on foot and using sand-based tracking strips to examine footprints. For the first time, we used passive acoustic monitoring to try and detect it.
The study arose from discussions at an Indo–US Science and Technology Forum. A bioacoustic workshop, held at the Indian Institute of Science Education and Research–Tirupati, brought critical contributors together: P. Jeganathan, Russell Charif from K. Lisa Yang Center for Conservation Bioacoustics at Cornell University, and Robin and the rest of our team who are based around the study area. We focused on developing a systematic detection plan using automated recording units that tested four types of recording hardware for collecting acoustic data and two commercially available software programmes to analyse the sound recordings.
Based on a sound attenuation experiment conducted in the same landscape, we determined the recording radius of the four types of recorders to be 500 m. The area was divided into 1 × 1 km grids, with recorders placed at the center of each grid square. Our fieldwork was intense, involving the deployment of 17 recorders at a time. We were always careful to conceal the recorders, as the Sanctuary’s periphery is frequently visited by cattle and herdsmen.
We collected over 2,400 hours of data over the course of 5 months and created a detection pipeline using recognizers created in two commercially available sound analysis programmes: Raven Pro and Kaleidoscope Pro. Both programmes resulted in several million detections that we then manually cross-verified with vocalizations of co-occurring species that fall within the calling frequency bandwidth of Jerdon’s courser. To do this, we shortlisted co-occurring species that vocalize within the same bandwidth as our elusive target, using eBird, an online database of bird observations, and our personal field records. For calls that we could not readily identify, we prepared a questionnaire and sent this to 11 experts familiar with bird vocalizations in India, asking them to rate the call as most or least likely to belong to Jerdon’s courser.
Although we did not detect any of its known vocalizations, we did record an unidentifiable call that was similar to that of Jerdon’s courser. Having closely examined the context of the call, we believe the call to be that of a bay-backed shrike, a well-known mimic. This mimicked call only occurred once, which is insufficient to either confirm or rule out the presence of Jerdon’s courser in the landscape. However, it emphasizes the importance of taking into account mimicry when detecting species that vocalize infrequently. It also raises questions on how the shrike learnt this call—either from another bird that mimics the Jerdon’s courser, or directly from a Jerdon’s courser itself? To complicate matters, Jerdon’s courser is thought to be nocturnal and the bay-backed shrike is diurnal. There is no simple answer to ‘Did you find Jerdon’s courser?’. All options may be possible, but our study certainly indicates that it is worth continuing to monitor and use bioacoustics in future research.
Given the time constraints and the onset of the Covid-19 pandemic, we were unable to run the recorders year-round in the landscape, but we are looking forward to expanding the area covered to regions outside the Wildlife Sanctuary. The Indian Government and the State government have sanctioned substantial funding for research directed towards the detection of Jerdon’s courser, and national enthusiasm to detect this elusive species is very high generally. During our study, several news reports suggested, incorrectly, that we had detected this species. Although this was not what we hoped for, our study provides a crucial baseline for future research: the acoustic methodology can be built upon and used in conjecture with other methods to increase the chances of detecting this species.
The article Species detection framework using automated recording units: a case study of the Critically Endangered Jerdon’s courser is available open access in Oryx—The International Journal of Conservation.