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Grauer's gorillas (Gorilla beringei graueri) have declined drastically across their range in eastern Democratic Republic of Congo (DRC). Survey data analysed in 2016 estimated a 77% decline in numbers between the mid‐ 1990s and 2016 and predicted that Kahuzi‐Biega National Park (KBNP), and the contiguous Oku Community Reserve (OCR) held much of the global population. An estimate of 3800 Grauer's gorillas was made across its range at that time. Here, we publish the most extensive survey of Grauer's gorilla numbers to date, using nest counts from 230 line transects across KBNP and OCR to derive more accurate estimates of both gorilla and chimpanzee numbers. Gorilla numbers were estimated from line transects at 1,571 (95% confidence interval [CI]: 824–2,993) within KBNP and at 2,244 (95% CI: 1,471–3,422) in OCR. Eastern chimpanzee (Pan troglodytes schweinfurthii) numbers were estimated at 2,500 (95% CI: 1,804–3,462) in KBNP and 687 (95% CI: 472–999) in OCR. Estimates of total numbers for the survey area were 5,252 (95% CI: 3,687–7,481) Grauer's gorillas and 4,275 (95% CI: 3,322–5,502) eastern chimpanzees. Chimpanzee numbers were not significantly different from the estimates in the mid‐1990s but the gorillas had significantly declined, mostly in KBNP. Modeled densities of these apes indicated that distances to mines, villages, or roads significantly explained part of the distribution of these apes, with higher densities also found in more rugged and remote sites. Other primates have all declined in this region, likely due to bushmeat hunting, especially the Endangered Ulindi River Red Colobus Piliocolobus lulindicus. These results confirm the negative impact of insecurity on Grauer's gorilla but indicate that the population declines may not be as great as previously feared. Using our revised gorilla density estimate we revise the original estimate of global numbers from 3,800 to 6,800 individuals. Highlights: Grauer's gorilla number an estimated 5,252 (95% confidence interval [CI]: 3,687–7,481) and eastern chimpanzees number 4,926 (95% CI: 3,656–6,634) in the Kahuzi‐Biega National Park (KBNP) and adjacent Oku Community Reserve (OCR).Grauer's gorilla is estimated to have declined by 80% in KBNP since the mid‐1990s but chimpanzees are estimated to have remained stable. The numbers of gorillas in OCR have remained stable and chimpanzees have increased.Most other primate species are estimated to have declined significantly because of hunting for bushmeat. [ABSTRACT FROM AUTHOR]

In the Democratic Republic of Congo artisanal and small-scale mining is estimated to provide a source of livelihood for 14–16% of the population, or 8–10 million people. In the eastern part of the country it is one of the main threats to large mammal species and their habitats, including forest elephants Loxodonta cyclotis and great apes, such as the Critically Endangered Grauer's gorilla Gorilla beringei graueri and the Endangered eastern chimpanzee Pan troglodytes schweinfurthii. We used semi-structured questionnaires to survey mining communities in and around Kahuzi–Biega National Park and the Itombwe Nature Reserve to understand better the socio-economics of artisanal mining in the region, as well as the impacts of mining on bushmeat hunting. Minerals exploited at the sites surveyed included cassiterite, gold, coltan and wolframite, and most mines were controlled by armed groups. On average, miners earned significantly higher revenue than non-miners. However, mining was seen as a short-term activity and most miners were in favour of leaving the sector for better opportunities. Almost all respondents stated openly that they consumed bushmeat regularly because of the lack of alternatives and believed that bushmeat hunting had caused declines and local extinctions of some large mammal populations, including great apes. Respondents stated they would reduce their consumption of bushmeat if domestic meats became more available. We recommend that future interventions should target mine sites to address bushmeat hunting, by improving access to sustainable meat sources, establishing micro-financing mechanisms to help miners leave the mining sector, and working towards de-militarizing these sites to facilitate law enforcement. [ABSTRACT FROM AUTHOR]

Primate census techniques have been developed over the past 35–40 years yet there is still some confusion and great variation in the methods used. This precludes comparisons between sites where different techniques have been used. This paper discusses the variations between the methods that seem to be practiced currently and then describes a census of primates in the forests of western Uganda. Primate density and biomass varied greatly between forests as well as within forests and this is probably related to food availability. Chimpanzee ( Pan troglodytes) density was strongly correlated with nest encounter rates from reconnaissance walks in the forest. This result can be used to estimate chimpanzee density in forests where it is difficult to survey this species (e.g., due to security reasons). A total of 4,980 chimpanzee was estimated for Uganda which is higher than previously guessed, but still of conservation concern. Only four forests had more than 500 individuals which gives concern for long-term population viability. [ABSTRACT FROM AUTHOR]

Data on nesting behavior and nests of the Sonso community of chimpanzees (Pan troglodytes schweinfurthii ) living in the Budongo Forest, Uganda, were collected between October 1995 and December 1996. Analysis of the selection of nests shows a preference for particular tree species, especially Cynometra alexandri . Male chimpanzees nested lower than females. Day nests were found to be structurally simpler than night nests and were built in tree species used for feeding, at the same height as feeding activity. Day and night nests serve different functions, and should be clearly distinguished in studies of nesting behavior. Am. J. Primatol. 55:49–55, 2001. © 2001 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

A central issue in socioecology is the nature of the relationship between an organism's environment and its social structure. In chimpanzees, the fission-fusion social system is thought to minimize feeding competition for primary dietary components: ephemeral, dispersed patches of ripe fruit. Intragroup feeding competition is thought to force individuals into small parties. Informal observations in the Sonso region of the Budongo forest had suggested that in this habitat, food supply was such that feeding competition was less important in determining grouping patterns than elsewhere. We used data collected on food supply and party sizes over a 4-year period to investigate this suggestion. In accord with theoretical expectation, sizes of foraging parties fluctuated with the size of food patches. However, party sizes showed either negative or no relationship with habitat-wide measures of food abundance. Likewise party sizes showed little relationship to overall measures of food dispersion. For important dietary items, both fruit and leaves had patchy distributions, though the degree of clumping was not strong, and fruit was not more clumped than leaves. Generally, abundant food appeared to be less patchy, and chimpanzees appeared to use more patches as food became more abundant rather than forming larger parties. We suggest that both dispersal and abundance need to be considered when investigating the impact of food supply on grouping patterns, and that the importance of food as a factor in determining chimpanzee grouping patterns declines with increasing levels of abundance. [ABSTRACT FROM AUTHOR]