The curious case of the dog that did not bark 

Nighttime barking reveals new species of tree hyrax in Africa


Four different tree hyrax species are found throughout Africa, including a newly named species found living between the Volta and Niger rivers. Photo by Sharp Photography/Wikimedia Commons

June 14 (UPI) -- The novel nighttime barking of several tree hyrax populations in West and Central Africa first alerted scientists that the region's forests might host a unique, yet-named species.

Now, a new survey -- published Monday in the Zoological Journal of the Linnean Society -- has confirmed the hyraxes living between the Volta and Niger rivers are genetically and anatomical distinct from their relatives in neighboring forest regions.

Scientists recorded and analyzed calls from the newly named species, Dendrohyrax interfluvialis, found in the wet and dry forests of southeastern Ghana, southern Togo, southern Benin and southwestern Nigeria.

"Sometimes a keen ear is as important as a sharp eye," study co-author Eric Sargis, curator of mammalogy and vertebrate paleontology at the Yale Peabody Museum of Natural History, said in a press release.

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"My co-authors John Oates and Simon Bearder were in Nigeria in 2009 researching galagos, a group of primates, when they noticed that the hyrax calls were different on one side of the Niger from the other. All the evidence we subsequently studied, including the distinctive vocalizations, points to a unique species in the forests between the Niger and the Volta."

Hyraxes are unusual animals. Roughly the size of a groundhog, the tree-dwelling mammals are closely related to manatees and elephants. Though they're nocturnal, their eyes don't shine in the darkness, making them quite difficult to study.

Sargis and his colleagues compared the calls of the new species to hundreds of hyrax calls recorded between 1968 and 2020 at 42 sites in 12 countries.

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Measurements of duration, frequency range, repetition rates and other call characteristics confirmed that the "rattle-barks" of the new species were distinct from the shrieking calls recorded in the forests west of the Volta and east of the Niger.

The researchers also performed anatomical analysis of several dozen museum specimens, in addition to sequencing genetic samples from a handful of tree hyrax specimens.

The analysis confirmed the tree hyrax populations found between the Niger and the Volta are distinct from neighboring hyrax lineages.

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"There is increasing evidence that the Niger and Volta Rivers are significant biogeographic barriers to a range of mammals," said Oates, emeritus professor of anthropology at Hunter College in New York City.

"Hyraxes, for instance, don't cross water easily, so it makes sense that, through millions of years of changing climate, as African forests have expanded and contracted, new species would have differentiated in isolated forest fragments known as refugia, and then have been limited in their subsequent dispersal by large rivers."

The latest research has helped highlight the unique biodiversity found between the Niger and Volta Rivers. Unfortunately, the region's many novel species are increasingly under threat from human development.

Logging and the expansion of large-scale agriculture has fragmented the region's forests, and researchers say that stronger protections and large wilderness preserves are needed to ensure vulnerable ecosystems remain intact.