Tenrecs and otter-screws (Tenrecidae or Afrosoricida)
COHORT PAENUNGULATA
Afrotherian radiation that at the moment contains the orders (Hyracoidea, Sirenia and Proboscidea).
These are hyraxes, manatees and dudongs and elephants.
From Paleocene (66-56 ma), next 35 million years paenungulates dominated Africa’s large mammal fauna. They were herbivores: hyracoids, proboscideans and the extinct embrithopods.
Other mammals arrived from Eurasia and became more common about 25 mya.
Currently there are about 78 species of extant afrotheres. Most species are specialists.
Many have ecologically convergent forms on other continents.
This ecological specialization makes them vulnerable and prone to extinction in human modified world.
Re-evaluation is needed on the evidence on the morphological features that has been used as evidence for monophyly of Paenungulates.
However following features are most commonly used as evidence:
Female mammary glands between front legs
Tusks developed from incisors, rather than canines
Acoustic communication of tree hyraxes living in Kenya and Tanzania is amazingly diverse, loud, and unique among animals.
Tree hyraxes are curious relict species, it is related to elephants and manatees.
These tree hyraxes sing songs and in just in one location, number of calls may be more than 4000 during one night.
Tree hyraxes have been believed to be solitary, however this belief was based on very limited observations, and then repeated without questioning.
It also shows how little is known about tree hyraxes
As tree hyraxes are highly vocal, but difficult to observe, as they are nocturnal and live in the canopy of the forest, bioacoustics is the best method available to study their behavioral ecology.
This post explains the highlights of the open access, peer reviewed article in Mammalian Biology
In the tropical cloud forest acoustic competition is caused by rain, chorusing orthopterans and greater galagos (Otolemur garnettii).
Rain is very powerful acoustic competitor, when rain reaches 4 KhZ, tree hyraxes quit calling almost entirely.
Chorusing orthopterans usually use the band between 5 kHz and 12 kHz. This chorus, no matter how intense it is has no impact on tree hyraxes. They have adapted to each other during millions of years. The most important and loud part of the call is under 5 kHz, meaning that the message will get through even during loud chorus.
Greater galagos, Otolemurs are loud callers, and they do call on the same frequencies. However their calling is random and tree hyraxes can’t avoid calling at the same time.
Calls of the greater galago (Otolemur garnettii). Photo Hanna Rosti
Interestingly tree hyraxes call less during full moon, this may be a so called “ghost from the past” phenomenon. At some point there may have been a nocturnal, big predator bird, that was hunting also big tree hyraxes, that weight 2-5 kg. Now this predator is extinct, but behavior still continues.
This article focuses on incredible variable acoustic communication of Taita tree hyrax. If you are interested in other peculiar features of tree hyraxes please read this previous article of Taita tree hyraxes.
Taita tree hyrax is believed to be undescribed species for the science based on these calls. For nocturnal cryptic animals, that are difficult to observe, call analysis has been the typical method of making taxonomic evaluation. Each species have their typical calls, especially calls that are used for so called ‘advertising’. These are calls that are used to draw attention of other con-species.
Taita tree hyrax female. Life of tree hyraxes are almost completely unknown. We don’t know if both sexes are calling, or are they just males. Tree hyraxes are believed to be solitary, but continues calling is difficult to explain for animal that is believed to be solitary.
Basic territorial call that is heard frequently in the forests of Taita Hills is ‘strangled thwack’. This call is most likely call that tree hyraxes use to claim their territory. Tree hyraxes eat leaves, and they are dependent on tree cavities for daytime sleeping sites.
Strangled thwack is more than 100 dB call. Twist in the call, and noisy elements make sure that this call doesn’t go unnoticed.
Strangled thwacks are used in Taita Hills and in East Usambara Mountain. East Usambara Mountains are 160 km from Taita Hills. East Usambara Mountains are also part of Eastern Arch Mountains, and it is located in Tanzania.
Based on this very unique call type, Taita tree hyrax is believed to be tree hyrax species that is not yet described scientifically (Rosti et al. 2020).
Strangled thwack call from Taita Hills. Horizontal axel time (s), vertical axel frequency (kHz) A) One strangled thwack call. Call duration about 1 s. Noticechanges (frequency modulation) in the strongest frequency of the call.B) Sequence of strangled thwacks. Usually tree hyraxes use these calls in about 10 call sequences where they counter call with other tree hyraxes.
Strangled thwack sequence from one animal
Usually tree hyraxes are counter calling with each other.TaitaTree hyrax counter-calling
Another call type that tree hyraxes are using in Taita Hills is called hac. Hac call is used as territorial call. It is not quite as loud and frequency range is lower. Probably hac call is used when calling animal becomes little tired, or it want’s to use call type that is slightly less demanding.
Spectrograms of hac calls, time (s) on horizontal axel, frequency (kHz) on vertical axel.Hac call has smaller frequency range and it can be continued much longer, sometimes sequence may have more than hundred calls.
Songs from Taita tree hyrax
Taita tree hyrax sings songs. Songs have been previously found from rock hyrax (Procavia capensis) (Koren et al. 2008).
Singing mammals are very rare. Gibbons and whales sing. But I don’t know other singing mammals.
Singing Taita tree hyrax. Duration on horizontal axel (s) and frequency on vertical axel (kHz). These songs may last for more than 12 minutes.
Sound sample from Taita tree hyrax song.
Dendrohyrax song may begin like this.
Purpose of these songs are unknown. Probably they are used by males as they advertise their fitness for females that might be available for mating. In Taita Hills, remaining forests are packed with tree hyraxes and most likely all available territories are taken. It might mean that moving from one place to another could be difficult. Tree hyraxes may have to take a risk and come down to the ground where they are in greater danger to be hunted by genets. Acoustic communication is used as means to communicate with other tree hyraxes.
Tree hyrax wheezes, wheeze may be used as part of a song or alone
Taita tree hyrax wheezes with katytids on the background
More reading about tree and rock hyraxes:
Demartsev, Vlad, Arik Kershenbaum, Amiyaal Ilany, Adi Barocas, Einat Bar Ziv, Lee Koren, and Eli Geffen. 2014. “Male Hyraxes Increase Song Complexity and Duration in the Presence of Alert Individuals.” Behavioral Ecology 25 (6): 1451–58. https://doi.org/10.1093/beheco/aru155.
Hoeck, Hendrik. 2017. “Some Thoughts on the Distribution of the Tree Hyraxes (Genus Dendrohyrax) in Northern Tanzania.” Afrotherian Conservation, no. 13: 47–49.
IUCN. 2014. “Dendrohyrax Validus: Hoeck, H., Rovero, F., Cordeiro, N., Butynski, T., Perkin, A. & Jones, T.: The IUCN Red List of Threatened Species 2015: E.T136599A21288090.” International Union for Conservation of Nature. https://doi.org/10.2305/IUCN.UK.2015-2.RLTS.T136599A21288090.en.
Koren, Lee, Ofer Mokady, and Eli Geffen. 2008. “Social Status and Cortisol Levels in Singing Rock Hyraxes.” Hormones and Behavior 54 (1): 212–16. https://doi.org/10.1016/j.yhbeh.2008.02.020.
Roberts, Diana, Elmer Topp-Jørgensen, and D.C. Moyer. 2013. “Dendrohyrax Validus Eastern Tree Hyrax.” In Mammals of Africa Vol I. Vol. 2013. Bloomsbury.
Names of trees and woody climbers tree hyraxes are using in Taita Hills.
Woody climbers are very important for tree hyraxes as shelter, climbing and food.
Tree hyraxes needs larger forests, that are more than 90 ha in size
Tree hyraxes prefer tall trees with dense canopy coverage
Tree hyrax singing frequency reduces significantly as size of the forest decreases
Tree hyraxes are social, not solitary as previously believed
Tree hyrax conservation is urgently needed
1. Trees and woody climbers tree hyraxes are using in Taita Hills, Kenya. Meaning of woody climbers.
Most important trees for tree hyraxes are Macaranga capensis, Tabernaemontana stapfiana, Albizia gumnifera, Strombozia scheffleri, Syzygium cordatum, Celtis africana, Vitex keniensis, Milletia oblata, Pouteria adolf-friedericii and Newtonia buchananii.
Woody climbers are very important for tree hyraxes! In Taita Hills, tree hyraxes feed often on Dichapetalum eichii. Woody climbers are used by tree hyraxes for moving between and on the trees, and for resting. Woody climbers form tight nets around the trunks of the trees that may have width of several meters. In these tangled nets tree hyraxes may rest during the days and nights. They may form cave like formations, where tree hyraxes are completely safe and only slightly visible to thermal imaging camera.
This information can be used for conservation and reforestation purposes. When planting new trees, these indigenous trees are important for tree hyraxes – and to other animals as well. Conservation of woody climbers is very important for tree hyraxes as well. Previously tree hyraxes were thought to be dependent on cavities in trees, but our research with thermal imaging camera showed that woody climbers are just as important.
Tree hyrax from Mbololo Forest Taita Hills
Tree hyrax population size in Taita Hills
Tree hyraxes are most common in the largest forests of Taita Hills. Our analysis of calling rate / hour showed that as the size of the forest decreases, calling rate crashes. In forests less than 90 ha, tree hyraxes call rarely and they time their calls to the time when humans are not around, about 03 or 04 am.
This most likely indicates that in smaller forest, tree hyraxes have been poached close to the local extinction.
Tree hyraxes are isolated to their forests, outside forests in tiny patches of indigenous trees, there are some tree hyraxes. These populations are living in constant danger of human harassment and on the ground dogs will kill them fast.
3. Tree hyraxes prefer tall trees and dense canopy coverage
From airborne lidar, several characteristics from the forests were measured. In the analysis we used height of the forest and canopy coverage. Both had positive effect on tree hyraxes.
Highest calling rates were measured from locations were tree height was over 45 meters and where canopy coverage was dense. In these tall trees, often Pauterias, tree hyrax communities flourish.
4. Singing of tree hyraxes is most common in the most pristine indigenous forest
In the best locations, tree hyraxes sang during the study in more than 20 % of the hours. This means that on average, about two hours contained singing in good quality locations.
Tree hyrax songs can be long, and they have several different syllables that they may combine in different order.
In smaller forest, tree hyraxes were recorded singing only once.
This means that in the disturbed forests, natural behavior of tree hyraxes is disturbed also. This may be due to reduced population size or/and stress that individuals are experiencing in smaller fragments, with possibly higher possibility of getting poached.
Poaching of tree hyraxes still happens in Taita Hills. All thought it is not common. However tree hyraxes are slow reproducers, with just one or two offspring / year.
5. Tree hyraxes are social animals
Previously tree hyraxes were thought to be solitary animals, and their calling was believed to be territorial.
Our research with thermal imaging camera clearly showed that tree hyraxes live in groups.
These groups have guards, and these guards call when someone or something comes to their area.
We observed again and again how some animals are calling on guard, and some animals just nearby keep feeding or resting.
We also observed several animals together multiple times.
It actually makes more sense that tree hyraxes have similar kind of social organization as their relatives rock hyraxes and bush hyraxes.
6. Tree hyrax conservation is urgently needed, for them, but also for the sake of people and other species
Tree hyraxes are browsers, and they don’t cause any disturbance to people. They only eat leaves from indigenous trees.
Tree hyraxes and all other forms of life in Taita Hills would benefit enormously if forest cover in Taita Hills would increase.
This increase in forest cover is needed for survival of the remaining forests, as they are drying out in the lack of water. These forests are home to thousands of species.
Indigenous forests have a very strong pull for water, and increase of forest cover would increase rainfall in the area.
Deforestation has caused severe lack of water in Taita Hills and surrounding lowlands. Rivers are drying out and farming is becoming very difficult.
Tree hyraxes are isolated to their small forest patches, and without reforestation their survival is in danger.
At the coast of Kenya, last tree hyraxes are extremely endangered. They only survive in small fragments where they have shelted to protect them from the midday sun.
Tree hyraxes eat leaves of trees, thus they are browsers. They are excellent climbers in trees.
At the coast of Kenya, tree hyraxes only live in rocky formations, and caves.
Tree hyraxes are related to rock hyraxes, that live in rocky formations. Perhaps coming down to rocky formations is not that difficult to tree hyraxes.
These are first photographs and video published (as far as we know) of the Eastern tree hyraxes (Dendrohyrax validus) from Kenya.
You can read the full peer reviewed article from Ecology and Evolution
Tree hyraxes can be found from Shimba Hills National Reserve. However, it is not found throughout the forest.
Tree hyraxes are easy to locate based on their calls. However, seeing them is another matter.
Spectrogram and combination of calls that tree hyraxes at the coast of Kenya are using.
Outside Shimba Hills, only few tiny fragments of forest remain. Tree hyraxes are dependent of moist natural forests. Even though they may be able to survive in small fragments with caves and rock for some time, these isolated populations are doomed for extinction if all forest is cleared.
Tree hyraxes in the caves are social. Also in Simba Hills, I could follow the movement of the tree hyrax group by their contact calls. I suspect that these tree hyraxes, belonging to species D. validus (as fas as we know at the moment), has similar type of social structure as rock hyraxes.
Tree hyraxes (Dendrohyrax validus) from the caves in 2022
Tree hyraxes, taxonomy, acoustic communication and conservation 