A new species of giant sengi (genus Rhynchocyon)

Captive gray-faced sengi (Rhynchocyon chrysopygus)
Ndundulu Forest, Udzungwa Mountains, Tanzania.
Photo: F. Rovero, 19 March 2006.

In a pair of recent papers (Rovero & Rathbun 2006, Rovero et al. 2008) a new species of giant sengi (genus Rhynchocyon) has been described. The gray-faced sengi (Rhynchocyon udzungwensis Rathbun and Rovero 2008) has the most restricted distribution of the four species in the genus, being found mostly above 1000 meters in two forest blocks in the northern Udzungwa Mountains of south-central Tanzania, East Africa. The Udzungwa Mountains are the largest in the Eastern Arc mountain chain, which stretches from southern Kenya to southern Tanzania. These mountains support a remarkable amount of biodiversity and endemism, which now includes the gray-faced sengi.

The new sengi was discovered when camera traps were set out to assess fleeting visual sightings of a potentially unusual giant sengi. With the first photographs, it was clear that a new sengi had indeed been discovered, but actual specimens were needed to confirm this. A two-week expedition into the Ndundulu Forest was made in March 2006. The team of eight people was composed of four Tanzanians, two Americans, an Englishman, and the Italian expedition leader. On the 10 km hike into the area where the camera traps had been set, a partially eaten (probably by a raptor) sengi was very surprisingly found dead next to the trail - further confirming the discovery of a new species. Despite daily rain, and traps that turned out to be too small for the exceptionally large sengi, it took two weeks to capture four additional specimens with traditional snares. Between rain storms, the animals were photographed.

The four snared specimens were prepared in the field as museum study skins and then dried, but with great difficulty because of the soggy surroundings. The vouchers were then taken to The Natural History Museum (formerly the British Museum of Natural History) in London and compared with other specimens to confirm that the gray-faced sengi was indeed unique.

The new species is remarkably different than the golden-rumped sengi (R. chrysopygus), which is only found in coastal forests of Kenya, and the checkered sengi (R. cirnei), which is wide ranging in central and eastern African forests, including the Udzungwa Mountains below about 1000 meters. The gray-faced sengi superficially resembles the black and rufous sengi (R. petersi), which is found further to the north in the Eastern Arc Mountains and in coastal forests. None of the other giant sengis have a distinctive gray face with a jet-black lower rump. Also, the new sengi weighs about 700 g, compared to 300-500 g for the other three species.

The gray-faced sengi appears to be restricted to about 300 square kilometers of pristine wet montane forest in two separate areas. The Ndundulu-Luhomero area is protected by the West Kilombero Scarp Forest Reserve and Udzungwa Mountains National Park, whereas the Mwanihana area is entirely protected by the national park.

Although the size and color pattern of the gray-faced sengi are distinct from other giant sengis, preliminary observations suggest that many behaviors, including its diurnal activity, nesting, and foraging, are similar to the other three species.

The holotype specimen, which defines the species, is at the California Academy of Sciences (San Francisco), while the other four specimens (paratypes) are in the scientific collections of The Natural History Museum (London), the Field Museum of Natural History (Chicago), the Museo Tridentino di Scienze Naturali (Italy), and the University of Dar es Salaam (Tanzania).