The eastern tree hyrax is thought to be a solitarily living arboreal species of the forests of East Africa. However, on the coast of Kenya, indigenous forests have been almost entirely cleared, and some of the last tree hyrax populations live in limestone rocky formations and caves. Interestingly, they seem to be living in social groups. Here, we describe and document photographically these unique tree hyrax populations. We also describe their acoustical communication and their calling activity in three different habitats. Based on these animals’ physical appearance and acoustic analyses of their calls, they represent the species eastern tree hyrax, Dendrohyrax validus. Due to immence pressure from humans, the future of these small and isolated, cave-living tree hyrax populations does not seem bright.

Study sites

We visited three tree hyrax habitats on the Kenya coast in Jan 26–Feb 1, 2022. The first study site, the Shimba Hills Natural Reserve, 4.214° S, 39.451° E, has a total area of 192.5 km. The reserve supports forests (Figure 2a) and grassland areas that are kept open by periodic burning. The local tree hyraxes live in trees. The second site, Vipingo, is on private land (coordinates not published). It represents a 25-ha patch of old indigenous forest with large baobab trees (Figure 2b), surrounded by agricultural lands and villages. The site also has three large sacred limestone caves with bat colonies. The local tree hyraxes live in caves and trees. The third site, Chasimba, 3.739° S, 39.693° E, represents a small (2 ha) rock outcrop with sacred caves and small indigenous trees (Figure 2c), surrounded by agricultural fields and banana groves. The local tree hyraxes live in rocky formations higher up. Unfortunately, the site has already lost most of its tree cover and is in imminent threat of being turned into a limestone quarry, which would undoubtedly exterminate the tree hyrax population, as there are no other suitable habitats nearby.

We used a thermal imaging camera, Pulsar Helion 2 XP50 (Yukon Advanced Optics Worldwide, Vilnius, Lithuania) and Fenix TK25 RED (Fenix Lighting, Littleton, CO, USA) flashlights. For recordings, we used AudioMoth automatic recorders (v1.1.0 Open Acoustics Devices, Southampton, UK) and Song Meter4 (Wildlife Acoustics, Maynard USA).

Spectrograms and call analyses were done with Raven Pro 1.6. Different call types were identified, and clear recordings with no background noise were isolated. Tree hyrax calling activity for each hour was calculated by using band-limited energy detection function. A band-limited interactive detector was used with the following settings: min frequency 1000 Hz, max frequency 4500 Hz, min duration 0,01 s, max duration 2 s, min separation 0.23 s. Signal-to-noise ratio 70 %, SNR threshold above 10. False positive calls, (mostly short-eared greater galago Otolemur garnettii calls), were removed from the calculated calls by visually inspecting the calls.

We compared our photographic and video material of living tree hyraxes with photographs of tree hyrax skins that we have studied in the collections of the Natural History Museums in Nairobi, Kenya, and in the Swedish Museum of Natural History in Stockholm, Sweden. This allowed us to compare the physical appearance of the Kenya coast tree hyraxes with representatives of other tree hyrax populations and species.

Time in the file:

• a 18-19
• b 19-20
• c 20-21
• d 21-22
• e 22-23
• f 23-24
• g 0-1
• h 1-2
• i 2-3
• j 3-4
• k 4-5
• l 5-6
• m 6-7

This is a simple text file (txt), that can be opened on all computers.