Periodic censuses of threatened wildlife populations of high profile species help us to understand their population dynamics, assess the success of conservation programmes aimed at ensuring their survival, and ensure that they receive continued attention from the global conservation community. During the IUCN World Conservation Congress in September 2016, updates in the Red List of Threatened Species were made public. Not surprising was that the Grauer's gorilla (Gorilla beringei graueri) - the largest living primate - is now listed as Critically Endangered, the highest category, while the eastern chimpanzee (Pan troglodytes schweinfurthii) remains categorized as Endangered on the IUCN Red List. These two subspecies have full legal protection under the law n° 14/003 governing wildlife conservation and the ministerial decree n° 20/CAB/MIN/ECN-EF/2006 ascertaining the list of totally protected species in the Democratic Republic of the Congo (DRC).

Grauer's gorilla and the chimpanzee have been severely affected by human activities, most notably poaching for bushmeat associated with artisanal mining camps and for commercial trade. This illegal hunting has been facilitated by a proliferation of firearms due to widespread insecurity in eastern DRC for the past 20 years. The forest has suffered considerable human disturbance in the past in the form of mining, timber extraction, firewood collection, charcoal production, human-induced fire and poaching. The full impact of civil strife, political turmoil and recent poaching events was unknown; due to insecurity in this region, a complete census had not been conducted since 1996, therefore, there was a need to have an accurate estimate of the entire population. Thus, there was an urgent need to confirm the current status of the great ape populations by carrying out a systematic survey of the Itombwe Nature Reserve.

As good conservation practice aims to preserve as much ecological, morphological, behavioural and genetic diversity as possible (Oates 2006), the conservation of subspecies and populations is important. An estimate of the size of various populations throughout their historical distribution in the Itombwe Massif is therefore crucial. The conservation of the world's primates demands basics, elusive and hard-to-get information. Enormous efforts are underway to accumulate this information. Besides a basic understanding of the status and distribution of primates, we need to know where they live; their geography and habitat requirements, and in what numbers. Only with such data is it possible to identify and evaluate the threats to their continued existence. Field research on particular aspects of primate ecology, behaviour, reproduction and demography provide an understanding of how great apes respond to these threats and what conservation measures will be possible, effective and appropriate. Baseline density estimates and subsequent monitoring of primate populations are essential for assessing the impact of particular threats and measuring whether conservation programmes are succeeding. Much has been done in recent years to improve protection and management to avoid the Itombwe great ape populations becoming doomed to extinction.

The aim of the survey carried out in December 2015 was to assess changes in the population since 1996 and to increase our understanding of gorilla population dynamics in Itombwe, and the levels of human disturbance and their impacts on the gorilla and the effectiveness of conservation efforts. Gathering baseline information on the population size and long-term monitoring of a major great ape and umbrella or keystone species should be a priority for developing further management programmes that emphasize harvesting or habitat manipulation.

The Itombwe Massif, located in eastern DRC, to the west of the northern tip of Lake Tanganyika, holds the largest and most remote block of intact montane forest (> 1,500 m elevation) in Africa, and is one of the most diverse sites of the Albertine Rift. It extends between 2° 51.286' and 4° 0.690' south, and between 28° 09.889' and 28° 58.511' east. The Itombwe Mountains are thought to be one of the most important sites for biodiversity conservation in Sub-Saharan Africa (Stuart et al. 1990) and have been identified among DRC forests as a focus for the conservation of biodiversity and ecological processes (Doumenge 1990).

Itombwe's vegetation is very varied, ranging from low altitude to the highest summits (Doumenge & Schilter 1997, Mubalama et al. 2013). A diversity of vegetation types contributes to Itombwe's richness. Its forests include a continuum from lowland forest (less than 1,200 m), transitional forest (1,200-1,500 m), montane forest (1,500-2,200 m), bamboo forest and afro-montane forest vegetation (over 3,000 m). Above 1,500 m, approximately 8,500 km² of Itombwe is covered by montane forest, 1,500 km² by bamboo and 500 km² by gallery montane forest and grassland. Gallery montane forest and grassland hold some of the most beautiful and unique habitats of the region, including high elevation alpine meadows inter-digitated by tongues of forest, and large areas of upland savannahs which are nearly devoid of trees (Butynski et al. 1996).

Because of the sharply varied topography and the extent of the Itombwe Mountains, it is not simply a case of a single basic climate. There are considerable variations in rainfall patterns, humidity and temperature across the range, thus giving rise to numerous microclimates, which in turn have influenced the high biological diversity of the range. The hydrology of the mountains is complex, with an abundance of streams. The region is also ecologically important as a watershed, with the majority of the area falling within the catchments of the Ulindi and Elila rivers (Doumenge 1990).

Great Ape Survey Techniques

As a matter of principle, protected area management should be based on appropriate levels of information (evidence-based if possible). A first step will be to determine the distribution and abundance of species in order to help orient the patrols and to determine the most appropriate location of eco-guard posts in the various sectors of the reserve. In order to comply with such a requirement, WWF along with ICCN launched a field expedition to conduct a biological survey in the Itombwe Reserve in December 2015; the survey was a follow-up of a pre-inventory exercise carried out in November 2015. The objective of each expedition was to travel through a designated area and to record as much as possible of the large mammals and their signs as well as pertinent habitat, topographic features and human activity found along the path of travel.

The survey field teams' staff received hands-on data collection training on large mammal abundance and distribution. Initial reconnaissance was made to contact local authorities, and to recruit and assemble the team in Mwenga for training. Surveys in all the sectors lasted 3 weeks in December 2015, and were conducted by one or more field teams that included a principal investigator, a field team leader and a total of about 53 locally hired porters and guides who contributed occasional observations of animal signs.

Overall, the inventory was focused on the northern area of Kikuzi River with an emphasis on Zombe area, the south of Ulindi River, with an emphasis on Kakanga and Mount Ngusa/Mount Nolabi, and the area surrounding the Mwana River, especially Ibachilo-Ngomiano areas. A total of 1599 segments of 200 m divided into 14 cells of 25 km² was completed, thus covering an overall distance of 285 km of recce surveyed while using 911 men days protection effort. Field teams spent approximately 4.9-6.8 hours per day investigating the reconnaissance paths and recording data at a pace of 4.17 km per day. Fieldwork encompassed both the core zone and the multiple use zones of the reserve in Basile and Wamuzimu chiefdoms, and the Itombwe sector.

A simple data sheet was designed to enable standardized data collection on wildlife and habitat variables. As the surveys aimed to carry out a reconnaissance, it was decided that all signs, direct sightings of focal species and indirect evidence such as tracks and signs (including dung/pellets, night nests, evidence of feeding, trails, debarking) would be used to estimate relative abundance of large mammals in the survey areas. Tracks and signs were classed as fresh and old, and as single animal or group (> 1). A method used was the reconnaissance walks termed recce (following the path of less resistance), and every effort was made to follow trails in different locations. Survey routes followed wildlife trails and human tracks to survey a large area thoroughly. Cutting disturbance of vegetation along reconnaissance walks was minimized to increase the distance that could be covered on a given day. Most reconnaissance routes followed paths that looped back to or near the starting point, and in many cases it was necessary to cut paths so that the reconnaissance route could achieve this configuration. On those occasions when it proved necessary to cut a path, team members chose the route of least resistance (i.e. least undergrowth or other obstacles) in the general direction in which they were heading (Wilson et al. 1996).

Each sector was searched by walking an irregular network of reconnaissance routes across the area. The actual route was determined largely by the terrain and the availability of existing trails, while ensuring that the routes were sufficiently dense so that no area was missed that could have been large enough for a gorilla group to spend more than one week in. Total distance walked on each trail was measured using a combination of a hip chain (topofil) with biodegradable thread, topographic maps, and global positioning system (GPS) readings. Each team mapped as accurately as possible all paths taken and gorilla trails followed. We used the grid method of area of occupancy representation and calculation, whereby a grid of individual cells of 5 x 5 km is overlaid on observation points. By covering the area in this way, mapping and dating all gorilla trails and nest sites and by marking nest sites once they had been counted, it was possible to ensure that all groups were found and that no one was counted twice, and to distinguish similarly sized but distinct gorilla groups found close to each other. Where signs of two groups of similar size were found in close proximity to each other, and the dates of the nest sites did not allow them to be confirmed as different groups, they were assumed to be from the same group.

At each nest site, nests were counted and dung size measurements, along with the presence of silvery hairs, were used to establish the age-sex composition of the group as: silverbacks, "mediums", adult females, juveniles, and infants. Young individuals constructing their own nest were always considered as the combined category juveniles⁄subadults, and assigned to the dung size class "juvenile". Smaller dung found within the nest of an older individual was recorded as that of an infant. In the absence of infant dung, adult female nests could not be distinguished from those of a comparable sized (blackback) male, and were therefore classified as "medium".

The reconnaissance trails walked while looking for gorilla trails covered a large portion of the reserve and provided an opportunity to collect data on signs of human disturbance. Such signs were recorded, with the GPS location and estimated age of each. These included snares, paths and tracks of people, poachers' camps, bamboo and woodcutting, and any other signs of people using the forest illegally. Ages were categorised as recent, old, and very old. These survey methods were the same as those used for the pre-survey in November 2015, so that direct comparison could be made in the frequency and distribution signs of human disturbance over this period. Signs were analysed as encounter rates per km of reconnaissance trail walked. Total distance walked on each trail was measured using GPS readings.

For each sighting, the time, GPS position, altitude, mammal species or type of human sign identified, method of identification (sight, sound, dung, or nest), number of individuals identified, and sometimes habitat type where the species or sign was detected were noted. Sight was the most common method of identifying some mammals, including many primates. Clearly, however, with shy mammals such as chimpanzees, or nocturnal mammals such as bush pigs, sound, dung, tracks or nests were more common indicators of the species' presence (Plumptre et al. 2002). Throughout the study, our field teams consisted of experienced staff and several guides from the local community. Some guides were hunters, and their skills contributed a wealth of local natural history knowledge that provided the necessary foundation for making the assessment successful.

Levels of human pressure on the habitat and wildlife were assessed by recording distance to the nearest village, evidence of agricultural use in the vicinity, hunting signs (fresh and old), currently used paths through the study area and signs of recent mining. Signs of large mammals included fresh tracks, faeces, feeding, digging or territorial markings, animal parts, and other tangible evidence that mammal species were present. Animals were sometimes identified through vocalizations heard fortuitously. Some guides were adept at mimicking the calls of many local mammals, which allowed us to elicit responses or lure animals into a position for visual identification (Mubalama et al. 2008).

General information on the past and present status of large mammals' species and hunting methods was gathered in villages by interviewing hunters. Surveyors attempted not to ask leading questions and also verified the identification of species by asking for descriptions. Skins, trophies and other evidence were also examined whenever possible. An attempt was also made to assess the extent of hunting and trade in wildlife by talking to well-known hunters and local chiefs. Additional data on great ape group sizes and numbers were obtained by following recent anecdotal information in different locations. Groups of nests differing in nest number were considered to belong to different groups of gorillas, especially because they build nests, both day and night nests, which can be counted instead of live animals.

Habitat quality was assessed using a developed protocol. When walking along the transect, a botanical team recorded observation on forest types, canopy cover, understorey, regeneration, and ground cover. Water availability was noted whenever it occurred along the transect. Information was systematically recorded on standardized daily log forms designed by WWF/Protected Areas Rehabilitation Programme (PARAP).

Results and Discussion

The density of great ape populations was calculated and set respectively at 0.038 Grauer's gorilla per km² and 0.21 chimpanzee per km² in the Itombwe Nature Reserve. These densities are very low compared to encounter rates that were associated with a density of 0.3 gorillas and 0.4 chimpanzees per km² in the Itombwe Massif 1996 (Omari et al. 1999); thus, the status of Grauer's gorilla is of particular cause for concern. The considerable survey effort undertaken and supporting information provided by socio-economic research all provide additional confidence in the estimate. While the population has plummeted, the results should be viewed with caution, not only because all known reduction during the last decade can be attributed to one subset of the population, but also because the region is still plagued by political unrest.

Building upon the calculated densities, 9 subpopulations of Grauer's gorilla (Gorilla beringei graueri) were identifiedacross its geographic range and the estimated total population stands approximately at a minimum of 218 individuals. It is noteworthy to state that Grauer's gorilla was recorded with lower frequency during the inventory done on established paths across the forest. While some individuals may avoid paths, and other signs may be obliterated by human passage, the lower rates of sightings are likely due to a more rapid pace of travel and less careful searching for signs by observers walking on a well-established track.

Our Grauer's gorilla estimate is at odds with an estimate performed recently with patrol data that came from eco-guards as well as local communities in Itombwe (Plumptre et al. 2015). Although a substantial part of the reserve was covered, we believe that some gorillas could have been overlooked because detection probability and reporting rate by villagers were not taken into account. In addition, some of the villages visited during the survey reported a daring foray by gorillas into a farm of ripe maize, feeding on banana pith; widespread and recurrent complaints about crop-raiding gorillas and chimpanzees typically viewed as a "pest", "weed", or "ecological dislocate" (Else 1991) reflect their abundance in the region, mostly solitary adult males in search of cultivated highly palatable crops. Ameliorating crop losses incurred by primates and elevating local tolerance for wildlife incursions will require a sophisticated blend of technical, social and economic interventions.

The total population size estimated at 218 gorillas can be pooled into 5 hotspots of confirmed occurrence, and one additional area of probable occurrence in the area surveyed, that are reproductively isolated from each other by large rivers (Mwana, Elila, Kiandjo, Kikuzi and Ulindi). The most frequently recorded gorilla signs were tracks, nests and feeding signs. These results show a 74.6 % decline in Grauer's gorilla numbers between 1996 and 2015. The overall impression is that gorilla populations in Itombwe are well below their ecological carrying capacity, and in many areas there are no apparent geographical or ecological impediments to their increase in both numbers and range. The total Itombwe gorilla population therefore could be significant for conservation, in contrast to those in many other areas of the species' range. Successful conservation of Grauer's gorilla populations will necessitate a multi-disciplinary approach, including the exploration of creative alternatives to protect other forested communal lands. Surveys to assess the status of currently inaccessible populations, also focusing on the remote, steep hillsides that the Grauer's gorillas seem to prefer, including those in the Elila-Kiliza and Kiliza-Bitongo basins, as well as in Malenge area in the most southern part of the reserve where eco-guard presence is minimal, should be carried out as soon as security permits and survey funds are available.

The population of eastern chimpanzees in the Itombwe Reserve was estimated to be about 1,204 individuals at the time of the survey. This figure is consistent with recently estimated chimpanzee numbers from the occupancy analysis, set at 1,241 individuals (Plumptre et al. 2015). From that prospect, it is clear that the chimpanzee population has fared better in the Itombwe Reserve, increasing by about 9.4 % (between 1996 and 2015) in numbers compared to a 74.6 % loss of Grauer's gorillas. This is likely due to the social system of chimpanzees, which do not move in cohesive groups, but have a fission fusion social system and usually occur in small parties or alone. This makes it harder for poachers to track and find them, so they have not declined as rapidly (Plumptre et al. 2015). On the other hand, the association of Grauer's gorillas with inhabited villages and their near absence in adjacent mature forest supports the observations of Emlen & Schaller (1960) and Hall et al. (1998) that undisturbed montane forests represent low-quality habitat for Grauer's gorillas. The occurrence of gorillas across such degraded habitat, including recent fallow fields in the immediate outskirts of human settlements, could obviously increase the threat by human pressure (Omari et al. 1999). This argues strongly for conservation efforts aimed at ensuring the survival of as many Grauer's populations as possible and the maintenance of potential corridors of forest habitat between them (Hall et al. 1998).

Great apes live in groups that number between 10 and 40 individuals. Dealing with groups and what you measure along line transects and recce is tricky when making surveys of primates because different studies have used different methods and there has been no test of which method performs best (Sterling et al. 2013). In addition, some species are very hard to detect from observations on the ground as they flee and hide when they observe you coming, especially during patrol deployment. The great apes belong to this category, and despite their large body sizes they can be remarkably elusive, partly because their densities are low in forests and partly because they spend time on the ground and are hard to observe when there.

How many populations of a target species are needed to sustain that species within the planning region over the long term? Given that gorillas have approximately a 4-year inter-birth interval (Watts 1991), population growth will be inherently slow even at its maximum potential rate, and because each census requires a considerable investment of time and money, population censuses to monitor changes should normally be carried out approximately every 5 years. Based on demographic data from the Virungas, under optimal conditions gorilla populations are capable of a 3-4 % annual growth rate (Miller et al. 1998, Steklis & Gerald-Steklis 2001, Robbins & Robbins 2004). Recent analyses suggest that an effective population size of about 1,000 individuals is ideal to allow continued evolution, prevent the accumulation of harmful mutations (Allendorf & Ryman 2002) and avoid the negative effects of inbreeding depression and genetic drift (Soulé 1980).

Planners should exercise great caution when using this sort of rule of thumb, however, because genetic rules ignore uncertainty arising from a consideration of environmental and demographic factors. As a result, there are cases where viable populations will need to be much larger than suggested above. We still do not have data on the inter-birth intervals, birth rates, or mortality rates of the Itombwe gorillas to predict what the growth rate of the population could be. Obtaining such information requires decades of monitoring known individuals (Miller et al. 1998, Steklis & Gerald-Steklis 2001, Robbins & Robbins 2004). Possible factors that could constrain population growth include the availability of good gorilla habitat, disease and human disturbance. Little is known as yet about the quality of the vegetation in Itombwe for gorilla foraging; so there is a need to carry out research aimed at mapping the vegetation and investigating the gorillas' ecology and habitat requirements; this will provide us with a better understanding of the number of gorillas Itombwe could support.

Great apes are critically threatened and it is therefore important that their populations are monitored over time to assess how they are changing. Studies show however that the errors around primate survey data are such that it can be difficult to detect significant changes in the population unless they are fairly large. Plumptre (2000) showed that standard line transect techniques allow a change of only about +/- 10-30 % of the population to be detected in subsequent line transect surveys. In the case of surveys of indirect signs, such as nests, only +/- 30-50 % of changes in the population could be detected. In other words, the population would have to be almost halved before the results would reach significance at the 5 % level (Sterling et al. 2013).

In order to improve the ability to detect more subtle changes in the population size, a myriad of suggestions can be made, including

1. increasing the number of transects to ensure that at least 20 are sampled in each study area;
2. spatial modeling of line transect data allowing shifts in the distribution of populations to be identified;
3. repeating the counts along the transects to ensure that at least 60-80 % sightings of great ape groups are made, bearing in mind that, when analyzing repeated counts in distance, it is important to ensure that the repeated data from the same transect are entered as data from that transect and not as a new transect, and
4. focusing on one species would make it possible to stratify the sampling across the study area so that more transects are placed in an area where the density of that species is highest and fewer transects in areas where it is rare.

This can only be used on a species-by-species basis unless two species show the same pattern of abundance. In this regard, there is a need both to improve the rigor of existing methods and to develop new methods to improve the survey estimates of great ape populations as well as to determine group home range size depending on a thorough understanding of the extent of overlap between groups.

The negative effects of habitat clearance and fragmentation, as well as hunting pressures, will increase for all Grauer's gorilla and chimpanzee populations. Thus, the optimism offered by our remaining population size estimates as a core for conservation of the subspecies should not be accompanied by complacency. Continuation of the population reduction is expected because of the high levels of poaching, loss of habitat, and deterioration of habitat quality caused by expanding human populations as well as ongoing civil unrest and lawlessness in the geographic range of this taxon (Plumptre et al. 2015).

From a pragmatic standpoint, and to overcome this challenge, there is a crucial need to get personnel in the right place at the right time for catching law breakers and deterring others from even considering illegal activities. Not only does the manager need to know where the animals are, but he also needs to know where poachers may be found, thus making better use of the limited human resources. In addition to local hunters who trap and shoot wildlife for personal consumption or local trade, well-armed renegade groups operate throughout much of the Itombwe Massif and are known to illegally kill protected species. Although enforcement effort has been inconsistent since the creation of the reserve due to the current minimal presence and ineffectiveness of the eco-guards, access and resource use by local people are inadequately prohibited by anti-poaching units. The primary means of poaching in the reserve is through the use of wire snares. Snares are relatively inexpensive, readily obtainable in most markets, and may be set up under cover of darkness, which reduces the chances of detection. There is a crucial need to recruit and train more eco-guards, relocate the reserve headquarters from Mwenga to the reserve borders and establish a network of patrol posts from where informed patrols will be launched.

By making good data immediately useful, the Spatial Monitoring and Reporting Tool (SMART) will be boosting motivation, increasing efficiency, and promoting credible and transparent monitoring of conservation efforts. In this regard, both ICCN and WWF are committed to providing effective, legal, and safe support to wildlife law enforcement in order to deliver on the Itombwe Reserve conservation goals through Zero poaching strategy. There are 6 pillars to the achievement of Zero poaching, including:

1. assessment implying conducting regular effectiveness assessments;
2. technology in using the best available tools and technologies;
3. capacity by increasing field staff ability to protect wildlife;
4. community through engagement with local communities;
5. prosecution by improving approaches for prosecution; and
6. cooperation through sharing information regionally and nationally.

It must be mentioned that past experiences from around the world have shown that these 6 pillars must be addressed simultaneously in order to be successful. The increase in great ape populations can be directly traced to the sheer dedication of field staff operating on the ground. Therefore, there is a need to assess the effectiveness of LEM (Law Enforcement Monitoring), based on regular ranger patrols, compared with targeted patrols based on intelligence information. Such long-term monitoring of keystone species should be an integral part of the development of a comprehensive conservation programme for great apes in the Itombwe Massif. Without such monitoring, it is impossible to assess the effectiveness of current conservation strategies and to plan for future interventions.

Law enforcement is vital to curb illegal exploitation of wildlife populations. If poverty stands as the major driver of illegal hunting as households vie for income and sustenance while human population densities continue to grow, it is unlikely that such a relatively lucrative enterprise as poaching will subside, even if significant increases in anti-poaching efforts are made (Knapp 2007). Until poachers perceive that the costs, recounted here as potential injuries, fines, and prison sentences, to be higher than the financial benefits, poaching will likely continue unabated in Itombwe. It bears keeping in mind, however, that although outside the scope of this study, bushmeat demand could plausibly increase if poverty decreases in the region giving households more access to revenue. Such a scenario would likely affect the current costs and benefits a poacher faces.

The increased levels of human disturbance found during this survey are clearly a cause for concern. While more detailed analysis of the impact of human disturbance on gorillas, as well as the capacity of the available habitat within Itombwe to support numbers of gorillas, is needed before we can firmly conclude that disturbance is a serious constraint on population growth, these findings highlight the need for increased law enforcement effort as well as developing further ways of working with local communities to discourage illegal use of forest resources. Community scouts might also get more motivated to do their best, part of a new culture of accountability that ensures higher quality personnel, more productive patrols, and fewer opportunities for corruption. With more security and prospects for higher income, the community that established the reserve finally has a chance to realize the benefits they hoped it would bring. This approach is intended to reduce a great deal of the strain in the relationship between the reserve and local people in the hope that one day great ape population will become self-sustaining in the Itombwe Massif.

The long-term effectiveness of these measures depends heavily upon the interplay of three factors: the likelihood of detecting and arresting poachers, the severity of the punishment doled out, and the pecuniary and/or protein reward that the poachers may reap (Bennett et al. 2006). If the rewards poachers face are significantly greater than the financial, physical, and psychological risks involved, it is unlikely that the level of poaching in Itombwe will decrease appreciably. Understanding the magnitude of these factors is therefore critical to understanding and predicting future success of conservation initiatives.

Conclusion and Conservation Implications

Grauer's gorilla numbers have declined drastically, but there is still strong evidence that the Itombwe population will be recovering despite persistent gloomy rumours about their fate following the recent drastic reduction in wildlife range. It remains unclear how great ape status and distribution will change over the forthcoming decades given the obvious continuing tensions in the Great Lake region. Without significant and sustained conservation efforts, the opportunity to ensure the conservation of the great ape populations will be lost, especially if the decline at an average rate of 5 % per year continues (Plumptre et al. 2015). A number of practical actions in support of the conservation of the critically endangered Grauer's gorilla have taken place in recent months with the ongoing participatory elaboration of the Reserve Management Plan process.

In the near future, it is imperative that in-depth research continues as an essential monitoring service. The impact of poaching on the stability of the family social structure of great apes should be investigated in order to understand the dynamics. Our study emphasizes the need for coordinated surveillance and research efforts. Such a study requires a clear understanding of the social organization of Itombwe great apes, long-term observations, combined with a thorough knowledge of most individuals and groups and should be a clear research priority. As funding becomes available, we intend to complete a census using the "sweep method" to estimate the population size and distribution of the gorilla in the large tracts of potential gorilla habitat that are located in proposed communities' forests of different chiefdoms. This is an effort to complete our current picture of great ape distribution.

While patterns in the distribution of large mammals are beginning to emerge, the distribution and status of essentially all other taxa remain to be discovered. Given the region's high annual rainfall and range in elevation, a high diversity of plants including endemics is to be expected. Of particular interest will be the vegetations of the massif that is preferred by great apes throughout the reserve. There are still many issues to be addressed and tested to improve great ape survey methods. Ideally, methods would be tested on a population of known size, including how to deal with groups in the field-testing methods that treat each individual detected separately versus those that record the location of a group or subgroup center and multiply group density by an average group size - or lure count methods for groups that respond to playback calls. Overall, there is a need both to improve the rigor of existing methods and to develop new methods to improve the survey estimates of great apes.

A crucial part of our programme, which often dovetails with the reserve creation focus, is our conservation education activities. Last year, we initiated an awareness campaign through radio broadcasting with work in remote villages surrounding the reserve, and in early 2017 we will be extending this programme to other communities close to the reserve. Activities will be conducted by our "outreach team" in both schools and general community settings, with the support of local organizations. We are contemplating to develop a number of materials that are tailored to the local settings and conservation challenges.

The law enforcement world is moving more and more to the use of cameras to monitor sites. The technology is now available to have remote cameras that beam images in real time to the reserve headquarters, and these cameras can have a whole suite of sophisticated devices to reduce the chance of them being stolen or destroyed. There is a need to investigate the uses of such methods including fixed cameras. This would complement the eco-guard patrols and enable monitoring to take place at night as well as during the day. It is crucial to monitor progress to see where difficulties arise so that they may be tackled swiftly. A robust monitoring and evaluation system should be developed to ensure proper and timely roll out of Zero Poaching. There is a need to measure the deterrence effect of patrols at a site and to be able to assess the frequency of ranger patrolling that can effectively deter different illegal activities.

In summary, the census shows that it is possible for conservation efforts to succeed even under difficult conditions, while at the same time emphasizing the continued threats and challenges that this critically endangered population faces. These findings further highlight the need to strengthen conservation efforts as we look towards the future of improved reserve management and peace building in the region, and international support to provide increased protection for this unique, critically endangered Grauer's gorilla population. For many species, the only hope of maintaining such large populations is to increase the connectivity among geographically isolated populations (Allendorf & Ryman 2002).

Last but not least, bottom-up community-based initiative (CBI) programmes have made advances in community engagement and incentives for conservation, although there is a gap between these programmes in terms of wildlife crime. Therefore, enforcement programmes need to have positive engagement with communities and collaboratively work to identify problems and solve them together.

While community-based initiatives are well-intentioned, poverty remains at the root of poaching in western Itombwe. Lifting poachers and their respective households out of poverty through employment is essential for long-term conservation viability. For conservation to succeed in the short term, however, a maintained presence of anti-poaching enforcement should accompany such efforts to lift households out of poverty. For this to happen, local communities need to be part of developing strategies to reduce and prevent wildlife crime through addressing the following needs:

1. increasing the effectiveness of CBI in terms of reducing wildlife crime;
2. improving and strengthening the relationship and sense of service of enforcement programmes to communities;
3. using the best available science for understanding crime and criminal behaviour, and
4. moving toward poaching prevention.

Under current circumstances, the continued support of local traditional authorities for conservation activities is critical. Itombwe Nature Reserve has been through many ordeals, and has survived them all. Like the forest, its great ape populations have remarkable capacity for recovery and renewal.

Léonard K. Mubalama, Menard Mbende, Gentil Kisangani Milinganyo and Gedeon Banswe

The survey was a large collaborative effort, only made possible through the help, support and participation of a large number of people. Special thanks to the traditional authorities and people of the Itombwe Massif for their hospitality, warmth, and support throughout the field trip process. We also extend profound gratitude to all team members and support ICCN staff, guides and porters who worked long hard hours under difficult conditions to complete the survey. A tremendous thank you, as well, to the acting Administrator of the territory of Mwenga for his commitment and FARDC and police officials for all their help and hard work. Finally, a deep thank you to WWF donors (Netherlands and USAID) for their faith, encouragement, and assistance; without their support this project would not have been possible.

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