Remove/treat external/internal parasites to increase reproductive success/survival

Supporting evidence from individual studies

1. A before-and-after trial in 1984-1991 in coastal forest in Poço das Antas Reserve, Brazil found that the majority of reintroduced golden lion tamarins Leontopithecus rosalia, which were treated for parasites before release alongside 14 other interventions, did not survive over seven years. Fifty-eight out of 91 (64%) reintroduced tamarins did not survive in the wild over seven years. However, 57 infants were born (reproductive rate=63%) during the same period, of which 38 (67%) survived. Tamarins were quarantined, screened and treated for parasites, infectious diseases, possible genetically-based defects, injuries and diaphragmatic thinning and only released if they were clear of untreatable conditions. Different groups of captive-bred or orphaned tamarins were introduced in different years into habitat already occupied by the species and predators. Groups were provided with supplementary food, water and nesting boxes, and allowed to adapt to local habitat conditions before release. All tamarin groups were quarantined before release. Sick or injured animals were rescued, treated and re-released. The reserve became officially protected in 1983 and a long-term research study was implemented. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Beck B., Dietz J., Castro L., Carvelho C., Martins A. & Rettberg-Beck B. (1991) Losses and reproduction of reintroduced golden lion tamarins Leontopithecus rosalia. Dodo, 50-61.

2. A before-and-after trial in 1996-1999 in a tropical rainforest in Conkouati Reserve, Republic of Congo found that 70% of reintroduced wild-born orphaned chimpanzees Pan troglodytes troglodytes that were treated for internal parasites alongside eight other interventions, were still alive 3.5 years after release. Confirmed mortality was 10%, with a possible 30%. None of the adult females reproduced. Chimpanzees fed on 137 different plant species, a variety in diet similar to that of wild chimpanzees and had activity budgets that resembled those of wild conspecifics. No statistical tests were carried out to determine whether differences were insignificant. Chimpanzees underwent veterinary screens and vaccinations for poliomyelitis and tetanus. Before reintroduction in groups into habitat with low densities of wild chimpanzees, they spent 6-9 years on forested islands in the region to acclimatize. Orphan chimpanzees were rehabilitated and fostered at a nearby sanctuary. Researchers were permanently present on-site and monitored released chimpanzees using radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Goossens B., Ancrenaz M., Vidal C., Latour S., Paredes J., Vacher-Vallas M., Bonnotte S., Vial L., Farmer K., Tutin C.E.G. & Jamart A. (2001) The release of wild-born orphaned chimpanzees Pan troglodytes into the Conkouati Research, Republic of Congo. African Primates, 5, 42-45.

3. A before-and-after trial in 1994-1999 in mixed tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of reintroduced central chimpanzees Pan troglodytes troglodytes that were treated for parasites prior to release alongside 16 other interventions, survived for at least five years. Out of 20 reintroduced chimpanzees that were treated for intestinal parasites when necessary, 14 survived (70%). No statistical tests were carried out to determine whether the population change was significant. Individuals were radio-collared and followed at distances of 5-100 m. Rehabilitated orphaned chimpanzees underwent vaccinations and veterinary screens before being translocated in four subgroups from the sanctuary to the release site where resident chimpanzees occurred. Permanent staff monitored primate health, provided additional food if necessary and examined any dead chimpanzees. The area status was upgraded to a national park in 1999. Local people were relocated from the release site to a nearby village. In some cases, chimpanzees were treated when sick or injured. TV and radio advertisements were used to raise conservation awareness and local people were provided monetary and non-monetary benefits in exchange for their conservation support. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Tutin C.E.G., Ancrenaz M., Paredes J., Vacher-Vallas M., Vidal C., Goossens B., Bruford M.W. & Jamart A. (2001) The conservation biology framework of the release of wild-born orphaned chimpanzees into the Conkouati Reserve, Congo. Conservation Biology, 15, 1247-1257.

4. 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 received periodic deworming alongside 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 that in 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, age at first sexual swelling in females, and adolescent infertility were similar to that of wild chimpanzees. In total, 50 chimpanzees from various backgrounds were released in groups on three islandsinto habitat with natural predators (although these were rare), but with no wild or previously reintroduced chimpanzees. Chimpanzees were given antibiotic treatment when they suffered from severe colds, and were provided supplementary food every 1-2 days. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   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.

5. A study in 2002–2006 in closed canopy forest in Lékédi Park, Gabon found that one third of captive-bred reintroduced mandrills Mandrillus sphinx that were treated for parasites alongside other interventions, died within the first year post-release. During this year, mortality was 33% (12/36), with dependent infants being most affected. Fertility rate was 42% (5/12 females gave birth to an infant) and two of the five infants survived for longer than six months. Mortality decreased to 4% in the second year and fertility rate remained at 42%, and all five infants born in the second year survived for at least six months. Mandrill home range remained limited during the first two years after release. In 2006, the group numbered 22 individuals, including 12 of the mandrills originally released, all in good physical condition. All mandrills were treated for gastrointestinal parasites immediately before release. Mandrills were reintroduced as a group into habitat already occupied by the species and predators. They were allowed to adapt to local habitat conditions before release and supplemented with food until 2005. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Peignot P., Charpentier M.J.E., Bout N., Bourry O., Massima U., Dosimont O., Terramorsi R. & Wickings E. J. (2008) Learning from the first release project of captive-bred mandrills Mandrillus sphinx in Gabon. Oryx, 42, 122-131.

6. A before-and-after site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that were treated for parasites alongside 14 other interventions, survived for at least four years. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived over four years. Nine females gave birth to 11 infants, of which nine survived. Three groups received a deworming or a treatment for a skin condition, one and three years after release. Gorillas underwent disease screening and vaccinations during quarantine. They were released in groups, allowed to adapt to local environment and supplemented with food before release. To re-establish populations, gorillas were released into habitat with no resident conspecifics. Released gorillas were treated when sick. So-called ‘problem-animals’ were removed and relocated and dead gorillas were clinically examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-born. Both sites became protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   King T., Chamberlan C. & Courage A. (2012) Assessing initial reintroduction success in long-lived primates by quantifying survival, reproduction, and dispersal parameters: western lowland gorillas (Gorilla gorilla gorilla) in Congo and Gabon. International Journal of Primatology, 33, 134-149.

7. A site comparison in 2008-2012 in bamboo thicket-dominated forest at Dao Tien Island (DTI) and mixed forest in Dong Nai Biosphere Reserve (DNBR), South Vietnam found that several pygmy slow lorises Nycticebus pygmaeus that were treated for parasites prior to their release alongside eight other interventions, survived for at least two months. Four out of eight lorises survived for at least two months post-release, whereas the remaining individuals either died or their radio-collar signal was lost. Lorises were released in groups during the wet season after a 6-week quarantine, veterinary screens and oral treatment for parasites. Both release sites were protected, no wild resident lorises occurred there and predators were present. Lorises were kept in a cage at the release site between <2 months and two days, and were subsequently supplemented with food for 7-30 days in DTI and DNBR, respectively. Dead lorises were detected and examined. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Kenyon M., Streicher U., Loung H., Tran T., Tran M., Vo B. & Cronin A. (2014) Survival of reintroduced pygmy slow loris Nycticebus pygmaeus in South Vietnam. Endangered Species Research, 25, 85-95.

8. A site comparison study in 2008-2012 in mosaic forest at two sites in Cat Tien National Park, South Vietnam found that all pygmy slow lorises Nycticebus pygmaeus that were treated for parasites prior to their release alongside other interventions either died or disappeared. All five lorises died or their radio-collar signal was lost soon after release. Lorises underwent a 6-week quarantine, veterinary screens and oral treatment for parasites. They were released in groups into habitat with no wild resident lorises but with predators. Three lorises were released at Cat Tien National Park during the dry season. Another two individuals were held in a semi-wild enclosure for one month to foster behaviour that would facilitate their survival in the wild and were released during the wet season. Dead animals were examined to determine the cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Kenyon M., Streicher U., Loung H., Tran T., Tran M., Vo B. & Cronin A. (2014) Survival of reintroduced pygmy slow loris Nycticebus pygmaeus in South Vietnam. Endangered Species Research, 25, 85-95.

9. A before-and-after trial in 2008-2010 in tropical forest-grassland mosaic at Batéké Plateau National Park, Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla that were treated for internal parasites alongside ten other interventions, survived for at least nine months post-release. Four out of five (80%) juvenile gorillas survived for at least nine months after release when they were dewormed every three months. Three captive-bred and two orphaned wild born individuals were reintroduced as a group into habitat with predators and without wild conspecifics after they were allowed to adapt to local habitat conditions for some time. They spent the night in an enclosure equipped with nesting platforms, nesting material, supplementary food and water. Caretakers guided them into different forest patches on a daily basis. The study does not distinguish between the effects of the different interventions mentioned above.

   Study and other actions tested

   Referenced paper

   Le Flohic G., Motsch P., DeNys H., Childs S., Courage A. & King T. (2015) Behavioural ecology and group cohesion of juvenile western lowland gorillas (Gorilla gorilla gorilla) during rehabilitation in the Batéké Plateaux National Park, Gabon. PLoS ONE, 10.