Action: Regularly and continuously provide supplementary food to primates
- Two studies in China and The Gambia found that after regularly providing supplementary food, along with other interventions, primate populations increased. Two studies in Thailand and Malaysia found that populations declined after regular provision of supplementary food, alongside other interventions.
- Three studies in Brazil, South Africa, and Indonesia found that the majority of primates survived after being regularly provided supplementary food, along with other interventions.
- One study in Liberia found that after regular provision of supplementary food, along with other interventions, the majority of introduced chimpanzees survived for at least one year.
- One controlled study in Madagascar found that after a year of regular food supplimentation, along with other interventions, introduced black-and-white ruffed lemurs showed different diets compared to a resident wild group of the same species.
Supporting evidence from individual studies
A review in 1985 in tropical montane forest in Nanwan Nature Reserve, China on the status of rhesus monkeys Macaca mulatta found that regularly providing individuals with supplementary food along with designating the area an internationally protected nature reserve, resulted in an increase in their population by more than 90% over seven years. The population increased from ‘a few dozen’ in 1976 to 600-700 individuals by 1983, excluding the >100 monkeys that were captured and supplied to scientific and medical institutions. However, no statistical tests were carried out to determine whether this increase was significant. The area became an internationally protected nature reserve in 1976. The study does not distinguish between the effects of the different interventions mentioned above.
A study, which was included in a review, in 1967-1970 on Koh Klet Kaeo island, Thailand of captive lar gibbons Hylobates lar that were reintroduced on the island and which were continuously provided with food along with other interventions, found that their population decreased by 60% over three years. No statistical tests were carried out to determine whether this decrease was significant. Four infants were born to the introduced population of 20 gibbons (reproductive rate=20%). They were fed and provided with water from artificial food and water stations. Gibbons were introduced in successive pairs into habitat that did not resemble their natural habitat and without resident gibbons. Gibbons were obtained individually from commercial animal dealers and housed in a laboratory for at least one month together with the gibbon individual with which they were released on the island. In 1961, gibbons were designated protected animals in Thailand. The study does not distinguish between the effects of the different interventions mentioned above.
A study in 1987-1988 on an island in tropical forest in Liberia found that the majority of reintroduced western chimpanzees Pan troglodytes verus that were provided with food continuously after release alongside other interventions, survived for at least one year. Seven out of 30 released chimpanzees had difficulties to adjust to the new social environment and were brought back to captivity. Food was supplemented daily but chimpanzees also fed on wild food. Chimpanzees were screened for diseases before they were released in groups. Furthermore, they were socialized in naturalistic enclosures and were taught behaviour to facilitate their survival in the wild. On site, primates were allowed to adapt to the local habitat in enclosures for some time; younger and low-ranking individuals were released earlier to reduce stress. Sick and injured animals were temporarily removed to receive medical treatment. The study does not distinguish between the effects of the different interventions mentioned above.
A study in 1999 in tropical forest of Morro do Diabo State Park, São Paulo, Brazil found that only some of the individuals in a group of reintroduced wild and captive-bred black lion tamarins Leontopithecus chrysopygus that were supplemented with food along with other interventions, survived for at least four months. Four months after the release of three individuals, one tamarin died. Supplementary food was provided twice a day for one month and then daily for another two months. Tamarins underwent veterinary screens before translocation to an enclosure at the release site where they could adapt to the local environment where predators occurred. The group consisted of two wild females and one captive-born male. The latter was bred in a free-ranging environment where he had been fostered natural behaviour to facilitate reintroduction. The male was also treated when sick. Monkeys were fitted with radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.
A controlled study in 1998-2001 in tropical forest in Betampona Reserve, Madagascar found that diets of captive-bred, reintroduced black-and-white ruffed lemurs Varecia variegata variegata provided with supplementary food during the entire study period alongside other interventions did not overlap with that of the resident wild group in the first year after release. Captive-bred lemurs (one male and two females) fed only on around half of the plant species (N=57) that the wild group (ten individuals) fed on (N=109). Captive-bred lemurs remained dependent on supplementary food as their range was too restricted to encounter sufficient food and showed no inclination to increase their range despite efforts to encourage it. Lemurs were released in groups into habitat already occupied by the species. The study does not distinguish between the effects of the different interventions mentioned above.
A study in 1979-2004 in tropical forest on Baboon Islands, River Gambia National Park, The Gambia found that rehabilitated and reintroduced western chimpanzees Pan troglodytes verus that were regularly and continuously provided with supplementary food along with other interventions, increased from 50 to 69 chimpanzees over 25 years. No statistical tests were carried out to determine whether this increase was significant. Fertility and mortality rates were similar to wild chimpanzees, except for infant mortality (18%), which was lower than in wild populations. Inter-birth interval, average age at first birth, proportion males at birth and other reproductive parameters were similar to those of wild chimpanzees. In total, 50 chimpanzees from various backgrounds were released on three islands. Individuals were reintroduced in groups and into habitat with natural predators (although these were rare), but with no chimpanzees. Individuals received periodic deworming, and were given antibiotics for severe colds. The study does not distinguish between the effects of the different interventions mentioned above.
A controlled study in 1967-2004 in tropical forest in Kabili-Sepilok Forest Reserve, Malaysia found that rehabilitated and reintroduced orangutans Pongo pygmaeus morio that were continuously provided with daily supplementary food alongside eight other interventions, decreased by 33% over 33 years (1964-1997). Infant mortality (57%) was higher than in other wild and captive populations, and the sex ratio at birth was strongly biased towards females (proportion males: 0.11) compared to other wild and captive populations. However, inter-birth-interval (6.1 years) was similar to wild populations of the same subspecies. Mean age at first reproduction (11.6 years) was lower than in other wild and captive populations. Individuals underwent in-depth veterinary checks and were quarantined for 90 days before release into the reserve, where other rehabilitated orangutans lived. Individuals were captured and treated when injured or sick. Staff and volunteers received medical checks and tourists had to keep safety distances (>5 m) at all times. The study does not distinguish between the effects of the different interventions mentioned above.
A controlled study in 2004-2005 in secondary tropical forest in Bukit Tigapuluh National Park, Central Sumatra, Indonesia found that all captive Sumatran orangutans Pongo abelii that were regularly provided with food alongside other interventions, survived for at least three months post-reintroduction. Orangutans were supplemented with food during the reintroduction process at the release site. One group was guided into the forest on a daily basis where new food items were offered and their handling was demonstrated. All eight orphaned orangutans with largely unknown histories survived for at least three months post-release after which monitoring ceased. Orangutans underwent quarantine and health checks before being released into habitat to re-establish populations where previously released orangutans already occurred. One group was released after a 6-month acclimatization at a sanctuary. Another group was kept in semi-free conditions for 7-9 months prior to release and allowed overnight in the enclosure. Staff members guided the latter daily into the forest. The study does not distinguish between the effects of the different interventions mentioned above.
A before-and-after trial in 2008 in a coastal forest at Isishlengeni Game Farm, Kwazulu-Natal, South Africa found that 62% of rehabilitated vervet monkeys Chlorocebus aethiops that were reintroduced into the wild and whose diets were supplemented with food alongside other interventions, survived for at least six months. Five of 29 introduced individuals (17%) were reported dead. Of these, one died following predation and four were killed by domestic hunting dogs Canis lupus familiaris. Six individuals (21%) went missing. No females reproduced. Fresh fruit, vegetables, nuts and seeds were provided daily as supplementary food. Monkeys were introduced as one troop of 29 individuals into habitat with wild resident monkeys and predators. To acclimatize, monkeys spent two nights in a release enclosure (49 m2) before being released. Medical care was provided when necessary before release and while housed at the nearby rehabilitation centre. The study does not distinguish between the effects of the different interventions mentioned above.
- Bangjie T. (1985) The status of primates in China. Primate Conservation, 5, 63-77
- Eudey A.A. (1991) Captive gibbons in Thailand and the option of reintroduction to the wild. Primate Conservation, 12, 34-40
- Agoramoorthy G.H.M.J. (1999) Rehabilitation and Release of Chimpanzees on a Natural Island - Methods hold promises for other primates as well. Journal of Wildlife Rehabilitation, 22, 3-7
- Valladares-Padua C., Martins S.C., Wormell D. & Setz F.E.Z. (2000) Preliminary evaluation of the reintroduction of a mixed wild-captive group of black lion tamarins Leontopithecus chrysopygus . Dodo, 36, 30-38
- Britt A. & Iambana B.R. (2003) Can captive-bred Varecia variegata variegata adapt to a natural diet on release to the wild? International Journal of Primatology, 24, 987-1005
- Brewer M.S., Marsden D. & Emery T.M. (2006) Demographic and Female Life History Parameters of Free-Ranging Chimpanzees at the Chimpanzee Rehabilitation Project, River Gambia National Park. International Journal of Primatology, 27, 391-410
- Kuze N., Sipangkui S., Malim T.P., Bernard H., Ambu L.N. & Kohshima S. (2008) Reproductive parameters over a 37-year period of free-ranging female Borneo orangutans at Sepilok Orangutan Rehabilitation Centre. Primates, 49, 126-134
- Riedler B., Millesi E. & Pratje P.H. (2010) Adaptation to Forest Life During the Reintroduction Process of Immature Pongo abelii. International Journal of Primatology, 31, 647-663
- Guy A.J. (2013) Release of rehabilitated Chlorocebus aethiops to Isishlengeni Game Farm in KwaZulu-Natal, South Africa. Journal for Nature Conservation, 21, 214-216