PHYS 25 FEB 2020
Oustalet’s or Semliki? That is the question. It may not be on everyone’s lips, but it’s uppermost in the minds of conservationists after a rare red colobus monkey triggered a camera trap several hundred miles outside its known range.
The image was captured in a remote forest in South Sudan as part of the extensive and ongoing camera-trap surveys that began in 2015 as a collaboration between Fauna & Flora International (FFI), Bucknell University and the South Sudanese government.
Even for seasoned primatologists, Oustalet’s red colobus—the Central African version of these acrobatic, fiery-coated monkeys—is a riddle, wrapped in a mystery inside an enigma. A remarkable 20 subspecies of this highly variable species have been described, according to The Kingdon Field Guide to African Mammals.
These include the version known to its close friends as the Semliki red colobus, named after the river valley in Central Africa where an isolated population was first recorded, and which may or may not turn out to be a separate species.
While the experts are grappling with the complexities of colobus categorisation, there is no doubt that the monkey caught on camera represents a very exciting discovery, whatever the uncertainty surrounding which species or subspecies actually appears in the image.
Oustalet’s red colobus—named in honour of a nineteenth-century French zoologist—is officially categorised as Vulnerable on the IUCN Red List, but is described as ‘possibly extinct’ in South Sudan, which lies at the extreme north-east of its range.
Most of the known populations elsewhere are widely scattered and typically confined to remote, seldom visited areas.
This could explain why an apparently extinct monkey has remained undetected for so long before its cover was blown by a camera trap.
On the other hand, if—as the experts are speculating—the primate in the picture turns out to be the little-known Semliki red colobus, we have incontrovertible proof that this monkey occurs well beyond the previously accepted limits of its geographical range.
Either way, this is momentous stuff.
The latest photos, including the snapshot of the red colobus, are helping conservationists to compile an inventory of the previously undocumented species lurking in what is a relatively unexplored corner of Africa. The online citizen science platform, Zooniverse, is enabling the analysis of over half a million separate images captured by camera traps in this wildlife haven.