Never give up – an unexpected encounter with the lost Hill’s horseshoe bat 

As the Director of the Endangered Species Interventions Program at Bat Conservation International, I spend a lot of my time working with partners worldwide to prevent the extinction of threatened bat species. Like any rare species it is a challenging task but their nocturnal and elusive behaviour can make protecting bats especially challenging. This is the case for Hill’s horseshoe bat (Rhinolophus hilli). Only found in Rwanda, it had not been seen in almost forty years. There was growing concern among experts that this critically endangered species had disappeared forever.

Before I joined the programme, Dr. Paul Webala and Dr. Julius Nziza led the search for this unique bat within Nyungwe National Park, one of the last remaining intact forests in Rwanda. They searched areas where Hill’s horseshoe was last seen and other sites where bats had been recorded to make sure it had not been missed. Yet, after two years of surveys in the park, still no luck. This is when I joined the team. We decided more work was needed to be done to determine whether Hill’s horseshoe bat still existed. We designed a more ambitious project to help us search the 1,000km² of the National Park.

We first worked with the National Park Rangers who regularly patrol Nyungwe. We provided them with cave identification forms and asked them to record as many caves as they could while patrolling, giving us information on size, depth, and resident wildlife. This information would help us understand if the caves were a suitable habitat for the bats and worth surveying. The rangers identified a total of ten caves, one abandoned mine, and one building as promising bat roost habitat.

Armed with this new information, we brought together 10 field researchers and bat specialists in January 2019 from Rwanda, Kenya, Democratic Republic of Congo, and the United States. Over ten days and nights, we surveyed as many sites as possible, trying to catch any bat that resembled Hill’s horseshoe. While torrential rain made access to some sites challenging, we were able to survey most of the previously identified caves. But still, no bats resembling Hill’s horseshoe were found. As Hill’s horseshoe bat was thought to be cave roosting, we thought cave surveys were our best chance of finding it, so we increasingly feared the bat was likely extinct.

However, as well as searching known caves, the team also set up specialized traps every evening to catch bats as they fly along forest trails, just in case. We were able to catch 55 bats including the Damara woolly bat (Kerivoula argentata). It was the first time that species was recorded in Rwanda. Yet, the most exciting breakthrough came around 5am on the 15^th of January 2019 – not long before we would normally pack everything away and leave for the day, Sospeter Kibiwot, one of the Kenyan researchers, noticed something different about the bat in his hand. While obviously a species of horseshoe bat based on its intricate nose (see photo), the noseleaf was a lot larger than anything he had seen before. Being careful not to let the bat fly away, we started to pull out all our identification guides for bats of the region. Dr. Webala and Dr. Winifred Frick (Chief Scientist at Bat Conservation International) painstakingly measured every feature of the bat – while excitement was building within the team everyone knew that this was not going to be an easy process, after all only two Hill’s horseshoe bats had ever been captured so there were very few information to base our identification on.

Finally, we became confident that the bat we had in front of us could only be Hill’s horseshoe bat – last seen before many of the younger team members had even been born. After taking detailed photos and collecting a DNA sample, it was time to let it go. As an expert in bat acoustics, it was my job to record the first ever echolocation calls for Hill’s horseshoe bat. Making sure the acoustic recorders were working, I felt the importance of capturing these calls. Obtaining the unique call signature of the bat would allow us to carry out acoustic monitoring and identify the areas the bat is using. This information would greatly increase our knowledge of this rare species. To capture as many calls as I could, I ended up running after the bat when it was let go, following it as it flew along the path. I’m not sure I’ve ever ran that fast, or for so long, but capturing more calls made it worth it.

Since the end of the expedition, DNA analysis confirmed the species we held in our hands in Rwanda was indeed Hill’s horseshoe, confirming it is still living in the security of the park. Thanks to the dedication and commitment of the local rangers who have since been routinely conducting acoustic monitoring across the park, we now know that this bat is only located in a very small area, highlighting the vulnerability of the species. While everyone on the team is excited to be part of this rediscovery, we also agree that further research is needed to provide the additional information required for a strong species-specific conservation management plan to be implemented and the species to remain. We hope to provide those needed details during our next expedition to Nyungwe, in August 2022.

References:

• Aellen, V. (1973) Un Rhinolophus nouveau d’Afrique centrale. Periodicum biologorum 101–105.
• Baeten, B., Cakenberghe, V. V. & Vree, F. D. (1984) An annotated inventory of a collection of bats from Rwanda (Chiroptera). Revue de Zoologie et de Botanique Africaines 183–196.
• Flanders J, Frick W, Nziza J, Nsengimana O, Kaleme P, Dusabe M C, Ndikubwimana I, Twizeyimana I, Kibiwot S, Ntihemuka P, Cheng T, Muvunyi R, Webala P (2022). Bat species occurrences in Nyungwe National Park, Rwanda. Bat Conservation International. Occurrence dataset
• Rwanda Environment Management Authority (2015) Study to establish a national list of threatened terrestrial ecosystems and species in need of protection in Rwanda. REMA.