Abstract
Simple SummaryWild chimpanzee populations are dramatically declining due to anthropogenic pressure. One way of increasing wild population numbers and/or repopulating areas where local extinction has occurred is to release captive animals. HELP Congo was the first project to successfully release wild-born orphan chimpanzees in their natural environment. We studied the behaviour of eight released chimpanzees over eight years. Over time, they modified their behaviour, suggesting long-term behavioural and ecological adaptations. This suggests that successful release programmes may reinforce existing populations of endangered species.Wild chimpanzee populations are still declining due to logging, disease transmission and hunting. The bushmeat trade frequently leads to an increase in the number of orphaned primates. HELP Congo was the first project to successfully release wild-born orphan chimpanzees into an existing chimpanzee habitat. A collection of post monitoring data over 16 years now offers the unique opportunity to investigate possible behavioural adaptations in these chimpanzees. We investigated the feeding and activity patterns in eight individuals via focal observation techniques from 1997–1999 and 2001–2005. Our results revealed a decline in the number of fruit and insect species in the diet of released chimpanzees over the years, whereas within the same period of time, the number of consumed seed species increased. Furthermore, we found a decline in time spent travelling, but an increase in time spent on social activities, such as grooming, as individuals matured. In conclusion, the observed changes in feeding and activity patterns seem to reflect important long-term behavioural and ecological adaptations in wild-born orphan released chimpanzees, demonstrating that the release of chimpanzees can be successful, even if it takes time for full adaptation.
Highlights
The great apes have experienced a significant population reduction in the past 20 to 30 years and they continue to be threatened by poaching and habitat destruction [1,2]
We identified a total of 86 plant taxa (Table 3) from at least 42 plant families that were eaten by the eight chimpanzees
When comparing the feeding ecology in the released chimpanzees over time, we found a negative correlation between time since release and fruit consumption (Figure 2, rs = 0.311, p = 0.010, n = 67)
Summary
The great apes have experienced a significant population reduction in the past 20 to 30 years and they continue to be threatened by poaching and habitat destruction [1,2]. Great apes are frequently found in the pet trade, leading to large numbers of orphan animals arriving in sanctuaries. Attempts have been made to release wild-born orphan primates back into their natural environment [3,4,5,6]. Reintroducing wild animals in natural environments can be a useful tool for conservation because it can restore biodiversity [8], provide an important demographic and genetic reservoir for endangered species, and decrease the threat of extinction in endangered species [9]. Releasing animals into areas where there is a wild population may be done for a variety of other reasons, including animal welfare and supplementing wild populations where numbers are low; such cases may be referred to as reinforcement, supplementation or restocking [2]. We refer to both reintroduction and reinforcement programmes as release programmes
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