Estimating the population size of the Sanje mangabey (Cercocebus sanjei) using acoustic distance sampling

The Sanje mangabey (Cercocebus sanjei) is endemic to the Udzungwa Mountains, Tanzania, and is classified as Endangered due to its putatively declining population size, habitat degradation and fragmentation. Previous population size estimates have ranged from 1,350 to 3,500 individuals, with the last direct survey being conducted 15 years before the present study. Previous estimates are now thought to have underestimated the population due to a limited knowledge of group and habitat size, nonsystematic approaches and the use of visual methods that are not suitable for surveying the Sanje mangabey with its semi-terrestrial and elusive behaviors. We used an acoustic survey method with observers recording the distinctive “whoop-gobble” vocalization produced by mangabeys and point transect distance sampling to model a detection function and estimate abundance. Twenty-eight surveys were conducted throughout the two forests where Sanje mangabeys are found: Mwanihana forest in the Udzungwa Mountains National Park (n = 13), and the Uzungwa Scarp Nature Reserve (n = 15). Group density was found to be significantly lower in the relatively unprotected Uzungwa Scarp forest (0.15 groups/km²; 95% CI: 0.08–0.27) compared to the well-protected Mwanihana forest (0.29 groups/km²; 95% CI: 0.19–0.43; p = .03). We estimate that there are 1,712 (95% CI: 1,141–2,567) individuals in Mwanihana and 1,455 (95% CI: 783–2,702) in the Uzungwa Scarp, resulting in a total population size of 3,167 (95% CI: 2,181–4,596) individuals. The difference in group density between sites is likely a result of the differing protection status and levels of enforcement between the forests, suggesting that protection of the Uzungwa Scarp should be increased to encourage recovery of the population, and reduce the threat of degradation and hunting. Our results contribute to the reassessment of the species' IUCN Red List status and informing management and conservation action planning.     

Demographic Variation Among Udzungwa Red Colobus in Relation to Gross Ecological and Sociological Parameters

We evaluated variation in group size and composition of Udzungwa red colobus (Procolobus gordonorum) in relation to gross-habitat and sociological parameters. The endangered species is endemic to the Udzungwa Mountains and nearby forests in the Kilombero Valley of south-central Tanzania. We counted 63 groups in 10 forests, ranging in altitude from 250 to 1,800 m. Group size ranged from 7 to 83 (x = 36.3) individuals and adult sex ratios (females/male) ranged from 1.5 to 7.3 (x = 3.5), excluding solitary individuals. Group size was influenced by several habitat parameters, including tree density, degree of deciduousness, and forest size. Groups were largest in large blocks of mature, moist, mixed evergreen and semideciduous forests, but group size is not correlated with altitude. Groups in a highly degraded forest appeared to have fission-fusion societies. The effect of habitat quality on age-sex composition of groups was most apparent in natality and less so in survivorship of adult females and juveniles. The number of adult males in groups accounted for 50% of the variance in group size and 34–39% of the variance in numbers of adult females in groups. Habitat quality affects natality more than demographic parameters do. Groups with a low proportion of adult females had greater juvenile survivorship, perhaps because of lower food competition between these two classes. We proffer hypotheses based on our study and previous intertaxonal comparisons to explain cause and effect relationships between habitat quality and demography. Finally, our study demonstrates the importance of large blocks of old-growth forest to the conservation of Udzungwa red colobus, and we make recommendations for conservation and research.     

Monkey Abundance and Social Structure in Two High-Elevation Forest Reserves in the Udzungwa Mountains of Tanzania

The effects of human activity on population and social structure are a pantropical concern for primate conservation. We compare census data and social group counts from two forests in the Udzungwa Mountains, Tanzania. The main aim is to relate differences within and between the forests to current theory on the effect of human disturbance on primate abundance and group size. The survey reveals the presence of the restricted-range red colobus, Procolobus gordonorum, in New Dabaga/Ulangambi Forest Reserve (NDUFR). The primate community of NDUFR is impoverished compared to that in Ndundulu forest. Red colobus and black-and-white colobus (Colobus angolensis palliatus) abundance and group size are lowest in NDUFR. Fission-fusion of red colobus social groups may be occurring in previously logged areas of both forests. Our observations are consistent with current theory on the effect of habitat degradation and hunting on primates, but the relative effects of the 2 factors could not be differentiated. We pooled the results with previous data to show that abundance of red colobus in the Udzungwa Mountains is lowest at high elevations. Low red colobus group sizes appear to be related to human activity rather than elevation. Black-and-white colobus and Sykes monkeys (Cercopithecus mitis) show no relationship with elevation. Future studies will require more detailed information on vegetation, diet and ranging patterns to interpret fully intraspecific variation in population demography and social structure in the Udzungwa Mountains.     

Abundance of Diurnal Primates in Mwanihana Forest, Udzungwa Mountains, Tanzania

Many individual researchers have used line transect counts to estimate forest primate abundance. They have devoted less attention to the interpretation of line transect data obtained by several observers, as is often the case in long-term monitoring programs. We present primate relative abundance data that 5 observers collected over 6 yr (not continuous) along 4 different transects each 4 km long in the Mwanihana Forest, Udzungwa Mountains National Park, Tanzania. Total distance walked during transect repetitions is ca. 700 km. The species we saw most frequently was the endemic Udzungwa red colobus Procolobus gordonorum (mean 0.59 groups/km walked), followed by the Angolan black-and-white colobus Colobus angolensis (0.43 groups/km) and Sykes’s monkey Cercopithecus mitis (0.35 groups/km). We sighted the endemic Sanje mangabey Cercocebus galeritus sanjei and the yellow baboon Papio cynocephalus infrequently, the latter being confined to the deciduous forest parts of the transects. We analyzed sighting frequency by gross habitat type, transect, season, and observer. Interobserver differences in the relative abundance of each species were moderate and the few cases of significant variations were due to discordance of only 1 observer from the others. Estimated distances of primate group sightings differ significantly among observers, thus preventing us from deriving estimates of absolute density. Frequency distributions of distance-class intervals are not significantly different among observers, which may indicate gross interobserver consistency in the width of the area sampled. We conclude that unless consistency in data collection is checked, as we did for 2 observers who collected data simultaneously, potential interobserver differences remain an underlying source of variance in the results that cannot be separated from other sources of variance.     

Comprehensive Conservation Profile of Tana Mangabeys

Forests along 60 kilometers of the lower Tana River, Kenya, provide habitat for one of the world’s top 25 most endangered primates, the Tana mangabey (Cercocebus galeritus). There is no current accurate estimate of the mangabey population, but a 1994 census estimated the population at 1,000–1,200. Their habitat has been severely degraded since then: visual estimates indicated that 30% of the forest area has been cleared and product use has increased in > 80% of forests surveyed. As the mean number of mangabey groups per forest is positively correlated with forest area and density of trees, this loss is damaging to the mangabey population. There has also been an increase in mangabey-human conflict, e.g., crop raiding, set traps, mangabeys chased by dogs. Mangabeys exhibit ecological flexibility, but behavioral data come from only a few mangabey groups. A new conservation approach is needed because past approaches, particularly the Tana River Primate National Reserve and a World Bank/Global Environment Facility Project, failed to protect the forests. The failure was mainly due to a disregard of the land-tenure issue within the Reserve, exclusion of local people from decision-making, and neglect of forests outside the reserve. Future actions must include community conservation programs and forest and corridor restoration. Research should focus on traditional management, status of primate groups in severely degraded forests, ecology of additional groups, and a population estimate to inform management as they implement more specific conservation strategies for the species.     

Sanje mangabey Cercocebus sanjei kills an African crowned eagle Stephanoaetus coronatus

We present the first ever reported observations of a hunting African crowned eagle Stephanoaetus coronatus being killed by a primate, in the Udzungwa Mountains of south-central Tanzania. An adult female eagle launched an attack on a young Sanje mangabey Cercocebus sanjei who was feeding in a tree, but was intercepted and bitten by an adult mangabey who was feeding nearby. The adult mangabey and the eagle then fell together 25 m to the forest floor below. The eagle subsequently died from her injuries, while the mangabey escaped and is thought to have survived. This rare event is briefly discussed in the context of previous accounts of primate-crowned eagle interactions.     

阿拉善马鹿(Cervus alashanicus)生境适宜性评价

阿拉善马鹿(Cervus alashanicus)目前仅分布于贺兰山地区,对该物种进行生境适宜性的评价和分析是物种有效保护的前提和基础。2013—2014年通过样线调查及巡山资料查询,确定阿拉善马鹿出现位点86个,结合13种环境变量数据,利用最大熵(maximum entropy,MaxEnt)模型,并根据最大约登指数划定适宜与不适宜生境区,对贺兰山地区阿拉善马鹿的生境适宜性进行评价。ROC曲线(receiver operating characteristic curve)检测证明模型预测精度较高,研究结果表明:阿拉善马鹿主要分布于贺兰山东坡的中部和南部,以及西坡的中北部,适宜生境面积为667.87 km~2,占研究区域面积的18.2%;矿区、坡度和海拔是影响阿拉善马鹿分布的最主要环境变量,矿区对阿拉善马鹿的影响最大,建议管理部门加大对此人为干扰的管控力度,控制和减少现有矿区的规模,以促进该种群的发展。     

Population Sizes and Distribution of Primates in the Lower Tana River Forests,Kenya

We studied the population size and distribution of diurnal primates in the lower Tana River forests, Kenya. They are the only remaining habitats for 2 threatened primates: the Tana River red colobus (Procolobus rufomitratus) and the Tana River crested mangabey (Cercocebus galeritus galeritus). We conducted censuses in 73 forest patches from January through March 2001. We estimate population size of the red colobus to be 788 individuals in 82 groups and that of the crested mangabeys to be 2,070 individuals in 59 groups. The data suggest that over a 7-year period (1994-2001), there was an 18% increase in the crested mangabey population and a 5% decline in red colobus numbers. Further, the red colobus range has expanded both north and south, whereas that of crested mangabeys has only expanded south. Fifty-six percent of crested mangabeys and 46% of red colobus groups were inside the Tana River Primate National Reserve (TRPNR). Other primates encountered included 170 groups of Sykes' monkeys (Cercopithecus mitis), 70 groups of yellow baboons (Papio cynocephalus) and 4 groups of grivets [Chlorocebus (Cercopithecus) aethiops]. Mean group densities of the 2 endangered primates and of baboons were higher inside than outside the TRPNR, reinforcing the importance of TRPNR for their conservation. An intervention program is required to stem further decline in the red colobus population and to protect small isolated groups in forest patches outside TRPNR.     

Vegetative predictors of primate abundance: utility and limitations of a fine-scale analysis

Determining ecological predictors of primate abundance is important for both theoretical and applied conservation management. For forest primates, research has focused on comparisons of primate abundance and vegetation in different forest blocks or forest compartments with different management histories. However, great variation in primate abundance often occurs within single forests, especially in mountainous areas or in areas with habitat mosaics due to past disturbance. Here we assess, for the first time, the usefulness and limitations of small-scale, within-transect analysis of vegetative parameters as predictors of primate abundance in a very heterogeneous forest habitat in the Udzungwa Mountains of Tanzania. Relative abundance of four species of diurnal primates was recorded over a period of 2.5 years by walking three census transects 48 times each. Tree size, density, species composition, and food plants were measured along the same census lines. The fine-scale relationship between primate abundance and vegetative variables was analyzed through generalized linear modeling applied to 58 segments of these three census lines. Each segment was 200 m in length. For all four primate species, we found significant associations between their abundance and selected vegetative variables. The abundance of the endemic and endangered Udzungwa red colobus Procolobus gordonorum was positively related to mean basal area of large trees (diameter at breast height greater than 20 cm) and to the species richness of their food plants. Considering the very great variation in primate abundance that was recorded among segments of the census lines, our approach proved useful in predicting the relationship between primate abundance and small-scale habitat differences. The main limitation of this study, however, was the relatively low-predictive power of the models for some species, especially the Angolan colobus Colobus angolensis. We discuss the potential reasons for this problem and suggest possible improvements for future studies.     

Developing landscape habitat models for rare amphibians with small geographic ranges: a case study of Siskiyou Mountains salamanders in the western USA

To advance the development of conservation planning for rare species with small geographic ranges, we determined habitat associations of Siskiyou Mountains salamanders (Plethodon stormi) and developed habitat suitability models at fine (10 ha), medium (40 ha), and broad (202 ha) spatial scales using available Geographic Information Systems data and logistic regression analysis with an information theoretic approach. Across spatial scales, there was very little support for models with structural habitat features, such as tree canopy cover and conifer diameter. Model-averaged 95% confidence intervals for regression coefficients and associated odds ratios indicated that the occurrence of Siskiyou Mountains salamanders was positively associated with rocky soils and Pacific madrone (Abutus menziesii) and negatively associated with elevation and white fir (Abies concolor); these associations were consistent across 3 spatial scales. The occurrence of this species also was positively associated with hardwood density at the medium spatial scale. Odds ratios projected that a 10% decrease in white fir abundance would increase the odds of salamander occurrence 3.02–4.47 times, depending on spatial scale. We selected the model with rocky soils, white fir, and Oregon white oak (Quercus garryana) as the best model across 3 spatial scales and created habitat suitability maps for Siskiyou Mountains salamanders by projecting habitat suitability scores across the landscape. Our habitat suitability models and maps are applicable to selection of priority conservation areas for Siskiyou Mountains salamanders, and our approach can be easily adapted to conservation of other rare species in any geographical location.     

黑龙江省老爷岭南部穆棱林区马鹿种群分布数量及生境适宜性评价

开展野生动物种群分布数量和生境适宜性评价研究是制定物种科学保护决策的基础和关键。以东北马鹿(Cervus canadensis xanthopygus)为研究对象,于2015—2020年在黑龙江省老爷岭南部穆棱林区,采用大样方调查方法收集马鹿在雪地留下的足迹信息分析马鹿种群数量;通过相机监测、足迹链跟踪和大样方调查3种方法综合收集马鹿活动点信息,利用最大熵(MaxEnt)建模分析马鹿生境适宜性。马鹿种群分布数量研究结果表明,穆棱林区马鹿种群密度为(0.0645±0.009)只/km~2,种群数量为47—61只,主要分布在研究地区南部的和平、龙爪沟和共和林场。生境分析结果表明：人为干扰因子中,居民区对MaxEnt模型的贡献率为44%,马鹿主要在距居民区距离约5 km和10—15 km的区域活动,在偏僻的林间小道和乡村道路马鹿生境适宜性较高,其对模型贡献率分别为16.8%和10.2%;植被因子中,在距常绿针叶林和针阔混交林距离4 km范围内,随距离增加马鹿生境适宜性逐渐降低。生境适宜性分析结果表明,研究地区马鹿适宜生境和次适宜生境面积为87.09 km~2,仅占研究区域的10.39%,主要...     

A novel landscape genetic approach demonstrates the effects of human disturbance on the Udzungwa red colobus monkey (Procolobus gordonorum)

A comprehensive understanding of how human disturbance affects tropical forest ecosystems is critical for the mitigation of future losses in global biodiversity. Although many genetic studies of tropical forest fragmentation have been conducted to provide insight into this issue, relatively few have incorporated landscape data to explicitly test the effects of human disturbance on genetic differentiation among populations. In this study, we use a newly developed landscape genetic approach that relies on a genetic algorithm to simultaneously optimize resistance surfaces to investigate the effects of human disturbance in the Udzungwa Mountains of Tanzania, which is an important part of a universally recognized biodiversity hotspot. Our study species is the endangered Udzungwa red colobus monkey (Procolobus gordonorum), which is endemic to the Udzungwa Mountains and a known indicator species that thrives in large and well-protected blocks of old growth forest. Population genetic analyses identified significant population structure among Udzungwa red colobus inhabiting different forest blocks, and Bayesian cluster analyses identified hierarchical structure. Our new method for creating composite landscape resistance models found that the combination of fire density on the landscape and distance to the nearest village best explains the genetic structure observed. These results demonstrate the effects that human activities are having in an area of high global conservation priority and suggest that this ecosystem is in a precarious state. Our study also illustrates the ability of our novel landscape genetic method to detect the impacts of relatively recent landscape features on a long-lived species.     

The species–area relationship and confounding variables in a threatened monkey community

This study investigates the species–area relationship (SAR) for forest monkeys in a biodiversity hotspot. The Udzungwa Mountains of Tanzania are well‐suited to investigate the SAR, with seven monkey species in a range of fragment sizes (0.06–526 km²). We test the relationship between species richness and forest fragment size, relative to human and environmental factors. We distinguish resident and transitory species because the latter have an “effective patch size” beyond the area of forest. Forest area was the strongest (log‐linear) predictor of species richness. However, forest area, elevation range and annual moisture index were intercorrelated. Previous knowledge of the relationship between elevation and tree communities suggests that the SAR is largely a result of habitat heterogeneity. Isolation by farmland (matrix habitat) also had a significant negative effect on species richness, probably exacerbated by hunting in small forests. The effect of area and isolation was less for transitory species. The human influence on species' presence/absence was negatively related to the extent of occurrence. Weaker relationships with temperature and precipitation suggest underlying climatic influences, and give some support for the influence of productivity. A reduced area relationship for smaller forests suggests that fragment sizes below 12–40 km² may not be reliable for determining SAR in forest monkeys. Further practical implications are for management to encourage connectivity, and for future SAR research to consider residency, matrix classification and moisture besides precipitation. Am. J. Primatol. 72:325–336, 2010. © 2009 Wiley‐Liss, Inc.     

大兴安岭南段马鹿生境适宜性分析与生态廊道构建

构建生态廊道在缓解生境破碎化对生物多样性的影响、维持濒危物种的遗传多样性、维护自然生态系统结构完整与功能稳定方面具有重要作用。以内蒙古大兴安岭南段分布的马鹿(Cervus elaphus)种群为研究对象,利用MaxEnt模型对其生境适宜性进行分析,并利用最小累积阻力模型构建潜在生态扩散廊道,探讨大兴安岭南段区域隔离马鹿种群的栖息地连通方案。结果显示,马鹿栖息地呈破碎化状态,种群有明显的隔离分布趋势,现有适宜栖息地具有海拔较低(800—1200 m)、坡度较缓(<15°)、靠近水源、植被类型多为靠近山林的灌丛或草地等特点。所构建12条生态廊道具有经过河流浅水节段、远离村落等特点,便于落实栖息地生态恢复管理措施。研究从区域尺度综合分析了大兴安岭南段马鹿栖息地现状及连通性,有助于优化适宜栖息地格局,促进马鹿扩散和栖息地连通,为该物种隔离种群及其栖息地保护规划提供现实指导和基础资料。     

Estimating Species Richness and Modelling Habitat Preferences of Tropical Forest Mammals from Camera Trap Data

Medium-to-large mammals within tropical forests represent a rich and functionally diversified component of this biome; however, they continue to be threatened by hunting and habitat loss. Assessing these communities implies studying species’ richness and composition, and determining a state variable of species abundance in order to infer changes in species distribution and habitat associations. The Tropical Ecology, Assessment and Monitoring (TEAM) network fills a chronic gap in standardized data collection by implementing a systematic monitoring framework of biodiversity, including mammal communities, across several sites. In this study, we used TEAM camera trap data collected in the Udzungwa Mountains of Tanzania, an area of exceptional importance for mammal diversity, to propose an example of a baseline assessment of species’ occupancy. We used 60 camera trap locations and cumulated 1,818 camera days in 2009. Sampling yielded 10,647 images of 26 species of mammals. We estimated that a minimum of 32 species are in fact present, matching available knowledge from other sources. Estimated species richness at camera sites did not vary with a suite of habitat covariates derived from remote sensing, however the detection probability varied with functional guilds, with herbivores being more detectable than other guilds. Species-specific occupancy modelling revealed novel ecological knowledge for the 11 most detected species, highlighting patterns such as ‘montane forest dwellers’, e.g. the endemic Sanje mangabey (Cercocebus sanjei), and ‘lowland forest dwellers’, e.g. suni antelope (Neotragus moschatus). Our results show that the analysis of camera trap data with account for imperfect detection can provide a solid ecological assessment of mammal communities that can be systematically replicated across sites.     

Primates in Human-Modified and Fragmented Landscapes: The Conservation Relevance of Modelling Habitat and Disturbance Factors in Density Estimation

Accurate density estimations of threatened animal populations is essential for management and conservation. This is particularly critical for species living in patchy and altered landscapes, as is the case for most tropical forest primates. In this study, we used a hierarchical modelling approach that incorporates the effect of environmental covariates on both the detection (i.e. observation) and the state (i.e. abundance) processes of distance sampling. We applied this method to already published data on three arboreal primates of the Udzungwa Mountains of Tanzania, including the endangered and endemic Udzungwa red colobus (Procolobus gordonorum). The area is a primate hotspot at continental level. Compared to previous, ‘canonical’ density estimates, we found that the inclusion of covariates in the modelling makes the inference process more informative, as it takes in full account the contrasting habitat and protection levels among forest blocks. The correction of density estimates for imperfect detection was especially critical where animal detectability was low. Relative to our approach, density was underestimated by the canonical distance sampling, particularly in the less protected forest. Group size had an effect on detectability, determining how the observation process varies depending on the socio-ecology of the target species. Lastly, as the inference on density is spatially-explicit to the scale of the covariates used in the modelling, we could confirm that primate densities are highest in low-to-mid elevations, where human disturbance tend to be greater, indicating a considerable resilience by target monkeys in disturbed habitats. However, the marked trend of lower densities in unprotected forests urgently calls for effective forest protection.     

江西赣江源区域两栖动物的群落组成和物种多样性特征

赣江发源于武夷山脉南段西麓的高山岭间,该区域独特的地理环境和气候特征蕴育了丰富的生物多样性。然而关于该区域两栖动物群落组成和物种多样性调查非常匮乏,不利于赣江源头两栖动物物种多样性的保护。于2016年4-9月期间在江西赣江源区域采用样线法调查了两栖动物的资源状况、群落组成及物种多样性特征,比较了它们在山地森林区、丘陵森林与农田区和盆地农田区3类栖息地之间的差异性。结果表明：赣江源区域分布有8科23种两栖动物,新增记录3个物种,包括尖舌浮蛙、寒露林蛙和九龙棘蛙,泽陆蛙和饰纹姬蛙为优势种。赣江源区域的两栖动物群落组成和物种多样性存在显著的季节间差异和栖息地间差异;两栖动物季节性繁殖是造成前者差异的主要因素,而土地利用类型、栖息地特征、空间距离、生活习性的物种特性等因素成就了后者差异的出现。因此,春、夏季一般有比秋季见到更高的两栖动物物种丰富度和多样性;山地森林区的两栖动物物种丰富度和多样性最高,盆地农田区次之,丘陵森林与农田区的最低。山地森林区应成为赣江源区域两栖动物多样性保护的优先区域。国家Ⅱ级重点保护野生动物虎纹蛙,在3类栖息地中均有分布,且在盆地农田区和山地森林区能见到更多个体,但农田区分布的虎纹蛙遭受到更大的威胁,建议加强对农田区虎纹蛙及其栖息地的保护。     

Phylogeography of the Angolan black and white colobus monkey,Colobus angolesnsis palliatus,in Kenya and Tanzania

Little is known about genetic variation in the 6–8 subspecies of Colobus angolensis, currently distinguished by pelage differences. We present a comparative genetic analysis of one of these subspecies, C. a. palliatus, in Kenya and Tanzania that assesses evolutionary relationships and patterns of mitochondrial genetic diversity in 103 individuals across its geographic range. Fecal samples from approximately 156 individuals were collected in four localities: (1) Diani Forest, Kenya; (2) Shimoni, Kenya; (3) Udzungwa Mountains National Park, Eastern Arc Mountains, Tanzania; and (4) Mount Rungwe, Southern Highlands, Tanzania. These samples represent at least six groups, with 5–15 samples from each. Comparative sequence analysis of a 1,795 base pair mtDNA fragment revealed 19 unique haplotypes in four populations. Phylogenetic analyses suggest that sampled Kenyan haplotypes are paraphyletic, with one Kenyan haplotype basal to all other sampled haplotypes. Analysis of molecular variance (AMOVA) suggests high levels of genetic variation among populations (Φ_ST 0.72, P<0.001). Genetic data are concordant with a subspecies level differentiation between C. a. palliatus populations in Kenya and those in Central and southern Tanzania, as earlier suggested based on pelage differences. This study highlights the evolutionary distinctiveness of Kenyan populations of C. a. palliatus relative to Tanzanian populations. Although C. a. palliatus habitat in Tanzania is currently better protected than in Kenya, our results suggest Kenyan and Tanzanian populations should be considered distinct units, and the protection of C. a. palliatus habitat in Kenya, as well as habitat connectivity between Kenyan populations, should be prioritized for conservation and management. Am. J. Primatol. 72:715–724, 2010. © 2010 Wiley‐Liss, Inc.     

Changes in forest fragment sizes and primate population trends along the River Tana floodplain, Kenya

The Tana River forest patches significantly decreased in total area by 1875 ha (34.5%), from 5439 to 3564 ha between 1979 and 2000. The area covered by forests outside the Tana River Primate National Reserve declined by 1246 ha (38%) from 3283 to 2037 ha. This loss was higher than that inside the reserve, where total forest area reduced by 629 ha (29%) from 2156 to 1527 ha. The numbers of Tana River red colobus (Procolobus rufomitratus) and Tana crested mangabey (Cercocebus galeritus galeritus) groups were significantly correlated with forest sizes suggesting that both red colobus and crested mangabeys are likely to be affected by forest loss and fragmentation. However, comparison of the 1974/75 and 2001 census data did not reveal any significant change in the number of groups of either the red colobus or crested mangabey. The two endangered primates may have developed strategies to cope with a shrinking habitat.