Sixty years of research on chimpanzees (Pan troglodytes) at Gombe National Park, Tanzania have revealed many similarities with human behaviour, including hunting, tool use and coalitionary killing. The close phylogenetic relationship between chimpanzees and humans suggests that these traits were present in the last common ancestor of Pan and Homo (LCAPH). However, findings emerging from studies of our other closest living relative, the bonobo (Pan paniscus), indicate that either bonobos are derived in these respects, or the many similarities between chimpanzees and humans evolved convergently. In either case, field studies provide opportunities to test hypotheses for how and why our lineage has followed its peculiar path through the adaptive landscape. Evidence from primate field studies suggests that the hominin path depends on our heritage as apes: inefficient quadrupeds with grasping hands, orthograde posture and digestive systems that require high-quality foods. Key steps along this path include: (a) changes in diet; (b) increased use of tools; (c) bipedal gait; (d) multilevel societies; (e) collective foraging, including a sexual division of labour and extensive food transfers; and (f) language. Here I consider some possible explanations for these transitions, with an emphasis on contributions from Gombe.

When Julius Caesar was stabbed, 23 times, on the Ides of March, at least one of the daggers is supposed to have gone into his groin. He wasn't the last Roman to have his privates attacked. And he wasn't the last primate. In competition for sexual access, gonads are occasionally targeted: canine incisions in monkey and ape scrota are not uncommon; and rumors had a number of Roman emperors—from Caligula and Nero, to Galba, Vitellius, Domitian, Commodus, Caracalla, Elagabalus, to Balbinus, Pupienus and Valerian over the course of the third century crisis—done in with their genitals at risk, or with their genitals cut off.

Taraba State, Nigeria, is an important conservation site for the Endangered Nigeria–Cameroon chimpanzee Pan troglodytes ellioti. Gashaka Gumti National Park, Nigeria's largest national park and home to potentially the largest contiguous population of the Nigeria–Cameroon chimpanzee, spans a significant portion of the eastern sector of Taraba and the adjoining Adamawa State. South of the Park, Ngel Nyaki Forest Reserve comprises two forest fragments and holds a small population of chimpanzees. We investigated the existence of patterns in population structure and dispersal within this region, using microsatellite loci extracted from non-invasive sources of DNA. Our results indicate that dispersal and thus gene flow between the groups of chimpanzees at the Park and Reserve is limited, at least more so than it is within the Park, and we identified a biased sex ratio at the Reserve, forewarning of potential conservation concerns in relation to demographic and genetic stochasticity. We discuss conservation actions that may be applicable to sustaining the population within Ngel Nyaki Forest Reserve.

Cross-species infection among humans, chimpanzees (Pan troglodytes) and baboons (Papio spp.) is potentially a significant public health issue in Africa, and of concern in the conservation of P. troglodytes. However, to date, no statistical comparisons have been made between the prevalence, richness and composition of parasite communities in sympatric populations of baboons and P. troglodytes. We compared parasite communities in sympatric P. troglodytes and Papio papio living in a wilderness site, in the Republic of Senegal, West Africa. We asked whether, in the absence of humans, there are significant differences between these hosts in their interactions with gastrointestinal parasites. We tested whether host, location, or time of collection accounted for variation in prevalence, richness and community composition, and compared prevalence across six studies. We concluded that, despite being closely related, there are significant differences between these two hosts with respect to their parasite communities. At our study site, prevalence of Balantidium, Trichuris and Watsonius was higher in P. papio. Papio papio harboured more parasites per host, and we found evidence of a positive association between Trichuris and Balantidium in P. troglodytes but not P. papio.

Apes are important long-distance dispersers of large seeds in African tropical forests. Seed size and shape are likely to affect the ease of swallowing for an animal species. If an endozoochorous seed is larger than the digestive tract of an animal, the seed cannot be swallowed, and a round seed is more difficult to swallow than an elongated seed of the same length. In order to test if such a correlation exists between the seed size and its shape, we investigated the length and width of chimpanzee-dispersed seeds at the Mahale Mountains National Park, Tanzania. Among the 14 species of seeds, longer seeds had significantly narrower relative widths, and thus, they were more ovoid. Since the chimpanzee is the largest arboreal frugivore at Mahale, their food selection might have influenced the shape of larger seeds. The chimpanzee's selective consumption of such fruits with longer, elongated seeds may have facilitated the selective dispersal of such plant species in that area.

Despite treatment with praziquantel (PZQ) at 40 mg/kg in food, several chimpanzees on Ngamba Island Chimpanzee Sanctuary (NICS) continue to excrete eggs of Schistosoma mansoni. To monitor disease, 8 animals were closely examined under anaesthesia in March 2011 with portable ultrasonography and by rectal snip biopsy. Schistosome genetic diversity had been previously assayed within 4 of these chimpanzees, finding extensive diversity with 27 DNA barcodes encountered, although none was common to all animals. Calcified schistosome eggs were found in the rectal snips from 5 chimpanzees and liver fibrosis was clearly documented, indicative of progressive disease in 6 animals, the latter being surprisingly advanced in a younger chimpanzee. All 8 animals were treated under anaesthesia by oral gavage with PZQ at 60 mg/kg dosing that was well tolerated. These animals were again re-examined in June 2012 using stool and urine sampling. Only 1 chimpanzee appeared to be free from infection and active egg excretion was confirmed in 6 animals. If intestinal schistosomiasis is to be controlled within this setting, a long-term disease management plan is required which should combine active case-detection with an insistent treatment regime with praziquantel for these chimpanzees, exploring perhaps the performance of even higher dosing.

Locating activity hotspots – areas of higher density, more intense use, or distinct social units – is a prerequisite for answering many questions in animal ecology. However, for many species, carrying out such research from direct observations in tropical habitat is time-consuming and unrealistic for non-habituated animals. This study aimed to locate chimpanzee home ranges from transect nest counts. For validation purposes, 233 line transects were sampled within the home ranges of four habituated social groups of chimpanzees in Taï National Park, Côte d'Ivoire. In total, 373 km of transects were surveyed over 188 days and 683 nests of chimpanzee were recorded. First, we characterized heterogeneity of nest distribution patterns, including variation in density and group size within the area. Second, we used scan statistics, a likelihood-based cluster technique to locate chimpanzee social groups and compared them with the known home range boundaries. Chimpanzee nest distribution was characterized by a positive density and group-size gradient away from the range periphery. Furthermore, nest distribution clusters corresponding to the four groups could be successfully identified, although additional clusters for, for example, low-density areas between social groups seem to be an unavoidable by-product. The approach taken can be extended to a wide spectrum of data stemming from direct observations, camera traps, acoustic or genetic sampling to derive information about structure and patchiness of wild animal populations.

The Critically Endangered western lowland gorilla Gorilla gorilla gorilla is found at high density in the swamp forests of Lac Télé Community Reserve, northern Republic of Congo. Preliminary surveys for apes on the Reserve periphery in the 1990s indicated that this area may also contain high densities of apes and we wished to verify this. Using distance sampling methodology we surveyed 1,029 km2 of the south-eastern Reserve periphery including Raphia swamp forests. We recorded 1,021 ape nests along 21 2-km transects. Results indicated that ape density estimated from nest group density, excluding old and very old Raphia nests (which may decay slowly), was very high: 6.81 weaned apes km-2 (95% confidence interval 3.93–11.84). Gorillas built most of the nests recorded: their density was estimated at 5.25 individuals km-2 (2.70–10.19). Most nests were constructed in Raphia swamp forest despite it covering only 25% of the study area. These are among the highest recorded densities of apes in Central Africa but, as nest decay rates in swamps are unstudied, we also estimated densities based on hypothetically slow nest decay rates and published data from other habitats. Gorilla densities may be linked to availability of monocotyledons as food and the natural protection from hunting offered by Raphia swamps. Gorilla density in swamp forest is spatially and temporally variable and surveys are required to estimate ape populations elsewhere in this habitat. Most Raphia swamps in Congo are unprotected, including the periphery of Lac Télé Community Reserve; protection and management are required to assure their continued availability for apes.

In 2004 the Ebola virus caused a drastic decline in western gorilla Gorilla gorilla abundance at Lokoué Bai, a clearing in Odzala National Park, Republic of Congo. This decline was detected by observations of gorillas visiting the clearing. We confirm that the sympatric chimpanzee Pan troglodytes population was also affected by the Ebola outbreak, and test whether the decline in the ape population would have been detected with line-transect surveys, the most commonly used wildlife monitoring methodology in Central Africa. We also evaluate the potential of transect surveys for describing the extent and pinpointing the timing of drastic population declines when this information is not known from other evidence. Both nest survey using the marked nest count method and standing stock survey of other signs of ape presence (dung, feeding remains, prints) were able to detect the decline. However, only nests and dung were reliable indices for estimating the magnitude of the decline and accurately pinpointing the timing. It was necessary to pool data across many survey replicates because of small samples sizes. Our results suggest that transects methods are able to detect drastic changes in ape abundance but that large sample sizes are necessary to achieve adequate statistical power. We therefore recommend that those intending to use transect methods as tools for monitoring large forest mammals evaluate in advance how much effort will be necessary to detect meaningful changes in animal abundance.

Over 8 months we surveyed the Lake Tumba landscape, Democratic Republic of Congo, walking 86 km of transects and 324 km of reconnaissance, to document the distribution and estimate the abundance of great apes. Five separate groups of bonobo Pan paniscus were located in the areas of Bolombo-Losombo, Mbala-Donkese, Ngombe-Botuali, Botuali-Ilombe, and Mompulenge–Mbanzi-Malebo–Nguomi, and one population of chimpanzees Pan troglodytes in the Bosobele-Lubengo area. Mean bonobo densities ranged from 0.27 individuals km-2 in the vicinity of Lake Tumba to 2.2 individuals km-2 in the Malebo-Nguomi area. In the latter they appear to be living at a higher density than reported for any other site. This may be due to the area's forest-savannah mosaic habitat, which may provide year-round fruit sources, with bonobos falling back on savannah fruits when forest resources are scarce. The bonobos of the Bolombo-Losombo area and the Bosobele-Lubengo chimpanzees have low relative abundances and live in marginal habitats of islands of terra firma within inundated forests.

During 1998–2000 extremely low densities of gorillas Gorilla gorilla gorilla and chimpanzees Pan troglodytes troglodytes were found in the Minkebe Forest block in north-eastern Gabon. When compared with data collected before 1994, these data suggest a catastrophic decline in ape populations in the area. We believe that this decline was caused by a disease epidemic. The period of decline corresponds with the Ebola outbreaks of 1994 and 1996 that occurred in the human population in the same area. Deaths of gorillas and chimpanzees were associated with both Ebola outbreaks. Data from nearby sites indicate that the epidemic was limited to the Minkebe Forest. Occurrence of such epidemic die-offs should be taken into account in conservation strategies for the long-term survival of ape populations. At the time of writing, an Ebola epidemic among humans in the Zadié Department east of Minkebe Forest has resulted in 53 deaths. In the neighbouring Republic of Congo, authorities have reported 43 deaths and at least 12 other cases of Ebola. These epidemics are believed to be linked to the handling and eating of dead apes.

Multiple species of primate disperse seeds and differentially contribute to the seed rain in tropical forests. The goal of this study was to examine seed dispersal by a primate community of five monkey and two ape species in the Dja Reserve, Cameroon. The density of primates in the reserve was calculated to be 77 individuals km-2. Analysis of 5789 faecal clumps demonstrated that 40% of monkey and 74% of ape faecal clumps possessed whole seeds. Six of the seven focal species acted as seed dispersers; faecal clumps passed by the black-and-white colobus (Colobus guereza) did not contain any whole seeds during the study. Seed passage trials on four captive monkey species showed monkeys to have an average seed passage time of 22 hours and defecation rate of five times per day. From the above results, the primate community was estimated to defecate 1129 seeds km-2 d-1. Seeds passed by the primate community came from 125 species of trees, lianas and shrubs, equivalent to at least 34% of the known tree flora. Rarefaction curves indicated that additional collection effort would identify more seed species passed by primates. Germination studies demonstrated that primate-passed seeds are viable. The number of seeds and plant species dispersed suggests that the primate community plays an important role in the maintenance of forest structure.