The findings show that there are more than three times as many Zanzibar red colobus monkeys (more than 5,800 individual animals) than previously thought, and many more monkeys living within protected areas than outside of them.
But the bad news is that their survivorship chances are rated as very low, with the species now extinct in at least four areas and forest habitat - on which the primates and others species depend - are rapidly being cleared for agriculture and tourism development projects. Hunting is also common.
The scientists have published a paper titled ‘Zanzibar’s endemic red colobus Piliocolobus kirkii: first systematic and total assessment of population, demography and distribution’ in the online version of the journal Oryx. The authors are Tim R.B. Davenport, Said A. Fakih, Sylvanos P. Kimiti, Lydia U. Kleine, Lara S. Foley, and Daniela W. De Luca.
According to Davenport, the director of WCS's Tanzania country programme and lead author of the study, scientists have known about the Zanzibar red colobus monkey for 150 years, yet this is the first systematic study of this “poorly understood species” across its entire range.
"The systematic assessment redefines almost everything we know about this amazing animal, and is now guiding effective management strategies for this species," he said.
Seeking to gain a better understanding of the status and ecological needs of the Zanzibar red colobus monkey, the WCS team of researchers spent two years (4,725 hours in the field) searching for and observing the arboreal primates.
The surveys focused on within and outside the protected areas on the main Zanzibar island of Unguja, and deployed a new sweep census technique to collect data on group sizes and structures, demographics, and locations with the help of GPS devices.
The results of the study are said to have provided proof that Zanzibar's protected areas are, to some extent, working. Some 69 percent of the population of Zanzibar red colobus monkeys live inside Unguja's protected area network, and monkey groups found within protected areas boasted both higher average group sizes and more females per group.
Conversely, the assessment also highlighted challenges for conservation, especially for the more than 30 percent of the monkey's population that live outside the protected areas. The scientists discovered that four of the forests previously known to contain Zanzibar red colobus monkeys, no longer do. Four other locations were found to contain only one family group each, which are unlikely to survive in isolation.
One of the largest threats to the Zanzibar red colobus monkey is deforestation. Forests in Unguja are being lost at a rate of more than 19 square kilometres per year due to agricultural activities, residential development, and human population growth. The hunting of monkeys for food and retaliation for crop raiding is also a concern.
The authors recommend creating a new protected area to further safeguard the Zanzibar red colobus monkey, as well as increasing primate and forest tourism operations. The team has also suggested making the primate the official national animal of Zanzibar.
"The Zanzibar red colobus monkey is unique to Zanzibar and could be a wonderful example of how conservation efforts can succeed in protecting both wildlife and habitat, which in turn benefits communities" said Davenport, who recently presented the study's results to the Zanzibar government.
He added: "The species could serve as a fitting symbol for both Zanzibar and the government's foresight in wildlife management."
WCS will work with the Isles government to initiate a flagship species programme that will protect both the primates and the archipelago's remaining forests.