Estimating densities of large herbivores in tropical forests: Rigorous evaluation of a dung‐based method

When sighting‐based surveys to estimate population densities of large herbivores in tropical dense forests are not practical or affordable, surveys that rely on animal dung are sometimes used. This study tested one such dung‐based method by deriving population densities from observed dung densities of six large herbivores (chital, elephant, gaur, muntjac, sambar, and wild pig) in two habitats, dry deciduous forests (DDF) and moist deciduous forests (MDF), within Nagarahole National Park, southern India. Using the program DUNGSURV, dung pile counts, decay rates estimated from field experiments, and defecation rates derived from literature were analyzed together by a model that allows for random events affecting dung decay. Densities of chital were the highest, followed by sambar. Wild pig densities were similar in the two habitats, sambar densities were higher in DDF, and densities of the other species were higher in MDF than in DDF. We compared DUNGSURV estimates with densities estimated using distance sampling in the same season. DUNGSURV estimates were substantially higher for all species in both habitats. These differences highlight the challenges that researchers face in computing unbiased estimates of dung decay rates and in relying on defecation rates from literature. Besides the elephant, this study is the first to rigorously test the efficacy of using a dung‐based approach to estimate densities of large herbivore species in Asia, and based on this evaluation, we provide specific recommendations to address issues that require careful consideration before observed dung densities are used to derive animal densities. Our results underline the need for an experimental study of a known population in a fenced reserve to validate the true potential of using dung‐based approaches to estimate population densities.     

Distribution of savannah elephants (Loxodonta africana africana Blumenbach 1797) within Nazinga game ranch,Southern Burkina Faso

We tested the hypothesis that elephant distribution inside the Nazinga Game Ranch (Southern Burkina Faso) during the wet season is influenced by villages outside, while in the dry season elephants are restricted only by water. Occupancy was evaluated by recording elephant dung‐piles on 54 line transects in each of three seasons: wet 2006, dry 2007 and dry 2008. We measured the distance of each transect from nearest villages, nearest permanent water sources, nearest guard posts and tourist camps. The results were unexpected: elephant occupancy in the wet season was independent of villages but influenced by poaching, while their occupancy in both dry seasons was determined by the proximity of villages as well as water. In the dry season, elephants were attracted to villages by grain stores and fruiting trees. There has been a dramatic shift in the dry season distribution of elephants, and consequently in browsing pressure, over the last two decades. We suggest that this change is a consequence of the expansion of human activities outside the ranch. This study shows that the effects of growing human disturbance on elephant populations in small protected areas are not predictable. Correcting for spatial autocorrelation had a negligible effect upon the models.     

Seasonality in elephant dung decay and implications for censusing and population monitoring in south-western Cameroon

Dung decay rates have been used in the past to correct elephant dung counts to estimates of population numbers. These assume that the dung is in a ‘steady state’ where production rates are equal to disappearance rates. The inter‐seasonal variation in decay rates, however, has never been fully investigated for elephant dung. This study, in the Banyang‐Mbo Wildlife Sanctuary in SW Cameroon, investigated whether a single dung decay rate is really appropriate when converting dung counts to population density estimates. A total of 870 fresh elephant dung‐piles were monitored until they had completely decayed, with at least 60 fresh dung piles located each month of the year between July 1994 to June 1995. The elephant dung decay rate obtained was 55.6% to 66.7% lower than those obtained for the rainforests of Gabon. This has implications for using decay rates obtained elsewhere to compute elephant densities from dung counts. Statistically significant differences were found in the mean duration of dung‐piles between different months and different seasons. Environmental variables, with the exception of rainfall, did not aid in predicting the duration of elephant dung‐piles. The model of Plumptre & Harris was used to estimate the standing crop of dung at any particular time of the year. The results show that, if there was no emigration of elephants from the population, then there was only a three‐month period when the dung was in a ‘steady state’. If emigration occurred during the wet season as is thought to occur then there was no period of ‘steady state’.     

Population structure and behaviour of crop-raiding elephants in Kibale National Park, Uganda

We examined patterns of crop raiding by elephants across gender and age classes in relation to elephant life history and sociobiology and estimated the quantitative contribution of crops to elephant diet in Kibale National Park (KNP). Elephant dung‐boli sizes were used to estimate age and sex, while the presence of crop remains in the dung of crop‐raiding elephants was used as evidence of repeated raiding. To estimate the expected proportion of elephants raiding per age class, the age distribution of raiders was compared with the age distribution of all KNP elephants. Elephants raiding crops were predominantly males. They began raiding in expected proportions at 10–14 years while a higher than expected proportion raided crops at 20–24 years. These results suggest that crop raiding is initiated at an age when male elephants leave their families and a large proportion of elephants raid when they are approaching reproductive competition. Evidence from dung of crop raiders, suggests that repeated raiding increases with age. Crop raiders derived 38% of their daily forage from the short time spent raiding, consistent with expectations of foraging theory. Males may be more likely to learn crop raiding because they are socially more independent and experience intense mating competition than females.     

Seed dispersal of Acacia erioloba by African bush elephants in Hwange National Park, Zimbabwe

Approximately two-thirds (64%) of all dry season samples of elephant dung analysed during a 3-year study in the Main Camp subregion of Hwange National Park, Zimbabwe, contained seed and/or pod materials from Acacia erioloba . Most seeds were recovered intact and actively germinating seeds were not uncommon. Very little pod mass relative to seed mass was recovered in most instances, with pod fragments recorded from only 56% of all exhaustively sampled elephant dung piles containing A. erioloba fruit materials. Nonetheless, large pod fragments and even entire intact pods were recovered occasionally from elephant dung. Seeds and pods of A. erioloba may comprise 12% or more of total wet-weight dung mass; individual dung piles were found which contained > 5000 A. erioloba seeds. Birds and smaller mammals search out and consume A. erioloba seeds present within elephant dung piles. The findings of this study indicate that potential digestibility of A. erioloba seeds for bush elephants ( Loxodonta africana africana ) may be much higher than expected from previous studies. In controlled feeding trials with captive bush elephants (age 11–15 years old) maintained on predominantly free-range dry season diets, the estimated efficiency of digestion for A. erioloba seeds consumed in pods was 81% to 96%, with a gut-transit time of between 24.5 and 36.0 h. On the basis of throughput times determined in experimental feeding trials, potential elephant-dispersal distances of 20–50 km are predicted for A. erioloba in the Kalahari Sands landscapes of southern central Africa.     

Large-scale spatial variation in palm fruit abundance across a tropical moist forest estimated from high-resolution aerial photographs

Fruit abundance is a critical factor in ecological studies of tropical forest animals and plants, but difficult to measure at large spatial scales. We tried to estimate spatial variation in fruit abundance on a relatively large spatial scale using low altitude, high‐resolution aerial photography. We measured fruit production for all 555 individuals of the arborescent palm Astrocaryum standleyanum across 25 ha of mapped tropical moist forest on Barro Colorado Island, Panama, by visually counting fruits from the ground. Simultaneously, we used high‐resolution aerial photographs to map sun‐exposed crowns of the palm across the same area, which were then linked to ground‐mapped stems. First, we verified that the fruit crop size of individual trees was positively associated with both crown presence on aerial photos and crown area visible on aerial photos. Then, we determined how well spatial variation in Astrocaryum fruit density across the study area was predicted by spatial densities of photo‐detected crowns and crown area compared to spatial densities of ground‐mapped stems and stem diameters. We found a positive association of fruit crop size with crown visibility on aerial photographs. Although representing just one third of all individuals in the study area, photo‐detected crowns represented 57% of all fruits produced. The spatial pattern of photo‐detected crowns was strongly correlated with the spatial pattern of fruit abundance based on direct fruit counts, and correctly showed the areas with the highest and lowest fruit abundances. The spatial density of photo‐detected crowns predicted spatial variation in fruit abundance equally well as did the spatial density of ground‐mapped stems. Photo‐detected crown area did not yield a better prediction. Our study indicates that remote sensing of crowns can be a reliable and cost‐effective method for estimating spatial variation in fruit abundance across large areas for highly distinctive canopy species. Our study is also among the few to provide empirical evidence for a positive relationship between crown exposure of forest trees and fruit production.     

Environmental factors affecting the distribution of African elephants in the Kasigau wildlife corridor,SE Kenya

The African elephant, Loxodonta africana, is under threat from habitat loss, poaching and human–elephant conflict. To mitigate for impact of habitat loss and reduce conflict, connectivity between elephant habitats can be improved through the protection of corridor areas. This study looks at elephant distribution and movement patterns within the Kasigau Wildlife Corridor (KWC) within the Tsavo Conservation Area in South‐east Kenya. Elephant presence data were obtained from observations by rangers during routine patrols across KWC, and were analysed in MaxEnt. The environmental factors predicting elephant distribution and density were tested, as well as the relationship between elephant maximum entropy and the presence and abundance of other wildlife. Seasonal variations in temperature and precipitation, plus presence of waterholes were found to play significant roles in elephant distribution across KWC. Higher elephant densities were not found to correlate with lower densities of other wildlife species; indeed, during the dry seasons, elephant presence was associated with greater wild herbivore densities. Besides illustrating the importance of the KWC for elephant conservation in the Tsavo ecosystem, both as a key corridor and habitat, this study also hopes to highlight the untapped utility of routine ranger patrol data, and encourage the use of such presence‐only data for deducing important knowledge for conservation of biodiversity.     

The effect of some ecological factors on the intestinal parasite loads of the Asian elephant (Elephas maximus) in southern India

Some ecological factors that might potentially influence intestinal parasite loads in the Asian elephant (Elephas maximus Linn.) were investigated in the Nilgiris, southern India. Fresh dung samples from identified animals were analysed, and the number of eggs/g of dung used as an index of parasite load. Comparisons across seasons and habitats revealed that parasite loads were significantly higher during the dry season than the wet season, but were not different between the dry-deciduous and dry-thorn forests in either season. After accounting for the effect of age on body condition, there was no correlation between body condition, assessed visually using morphological criteria, and parasite load in either season. Individuals of different elephant herds were not characterized by distinct parasite communities in either season. When intra-individual variation was examined, samples collected from the same individual within a day differed significantly in egg densities, while the temporal variation over several weeks or months (within a season) was much less. Egg densities within dung piles were uniform, enabling a simpler collection method henceforth.     

A population survey of forest elephants (Loxodonta africana cyclotis) in northern Congo

From February to April of 1989 transects were run in four forested areas of northern Congo (Brazzaville) to census elephant populations using dung counts. A total of 401.0 km of line transects was completed during the survey. An overall extrapolated density of 0.7 elephants/km² was obtained with a variation from 0.3 to 0.9 elephants/km². This study shows for the first time that elephants occur in high densities in a number of sites in northern Congo. When elephant dung density is plotted against distance from the nearest village for each transect a significant positive linear correlation results. Based on this correlation we hypothesize that the population of elephants in much of northern Congo is high. Local reports and our own observations indicate that elephant poaching is heavy in northern Congo and that the CITES ban on trade in African elephant ivory has had a limited effect on the level of poaching.     

How reliable are dung counts for estimating elephant numbers?

Dung counts are the most commonly used techniques for estimating elephant numbers in forests, yet there is considerable scepticism concerning their accuracy. Published accounts of dung counts show that they give estimates similar to those from other methods for vertebrates ranging in size from lizards to elephants. For ungulates, macropods and elephants there are strong correlations between estimates from dung counts and other methods. Thus, dung counts are as accurate or inaccurate as other methods for estimating vertebrate numbers, including elephants. Dung counts for elephants give estimates that are as precise as, and sometimes more precise than, those from aerial surveys of elephants. This is because the variance in dung density is usually low and results in a lower than expected variance for the final elephant estimate when combined with the variances of defecation and decay rates. Dung counts may be more appropriate than aerial surveys for monitoring small or declining elephant populations.     

Acoustic estimation of wildlife abundance: methodology for vocal mammals in forested habitats

Habitat loss and hunting pressure threaten mammal populations worldwide, generating critical time constraints on trend assessment. This study introduces a new survey method that samples continuously and non‐invasively over long time periods, obtaining estimates of abundance from vocalization rates. We present feasibility assessment methods for acoustic surveys and develop equations for estimating population size. As an illustration, we demonstrate the feasibility of acoustic surveys for African forest elephants (Loxodonta africana cyclotis). Visual surveys and vocalizations from a forest clearing in the Central African Republic were used to establish that low‐frequency elephant calling rate is a useful index of elephant numbers (linear regression P < 0.001, r_adj.² = 0.58). The effective sampling area was 3.22 km² per acoustic sensor, a dramatic increase in coverage over dung survey transects. These results support the use of acoustic surveys for estimating elephant abundance over large remote areas and in diverse habitats, using a distributed network of acoustic sensors. The abundance estimation methods presented can be applied in surveys of any species for which an acoustic abundance index and detection function have been established. This acoustic survey technique provides an opportunity to improve management and conservation of many acoustically‐active taxa whose populations are currently under‐monitored.     

Roles of environmental variables and land usage as drivers of dung beetle assemblage structure in mopane woodland

Colophospermum mopane woodland covers large areas of dry lowland savanna in southeastern Africa. Dominant land usage is conservation (45%) with the remainder mostly modified by farming. Dung beetle responses to environment (dung type, habitat, weather) and land usage (conservation, farming, mining) were examined at Phalaborwa (23.9431°S 31.1411°E) in the Phalaborwa‐Timbavati Mopaneveld, South Africa. Partitioning of gamma species richness and diversity showed lower alpha values in mine areas than in farm and conserved areas. However, between‐land usage differences in species richness, alpha diversity, abundance and biomass, showed lower significance than those between dung type and different weather. At two sampling scales, three multivariate techniques variously separated assemblages according to land usage, dung type and weather. Analysis of 21 mean samples separated clusters according to dung type (Canonical Correspondence Analysis, CCA) or mine assemblages, conserved plus farm assemblages on pig plus elephant, or cattle dung (NMDS, Factor Analysis) with shared variance of >80% and unique variance of 16–18% per cluster. In analysis of 188 samples (CCA), each overlapping dung type cluster was offset in ordinal space with congruent patterns of separation according to land usage and weather (drier days distant from moister days; conserved plus farm areas distant from early succession mine areas, which were distant from disturbed and later succession mine areas). Mining, dung types, and moist conditions were the strongest contributors to between‐assemblage differences. Compared with conserved areas, dung beetle diversity is appreciably altered by mining but only slightly altered by intensive game farming or livestock ranching with subsistence agriculture.     

Estimating the defaecation rate of the African forest elephant (Loxodonta cyclotis) in Banyang-Mbo Wildlife Sanctuary, south-western Cameroon

Defaecation rate is an important parameter in the conversion of dung counts to elephant numbers, yet estimates of elephant defaecation rates are available for a few sites, especially rainforest sites. The Banyang‐Mbo Wildlife Sanctuary in south‐western Cameroon is no exception in this regard. We tracked a radio‐collared herd of four forest elephants, counted their fresh droppings in two 24‐h periods each month in 36 consecutive months. Our results show a mean defaecation rate of 15.9 [95% CI (12.2–19.7)] dung piles per elephant per day. We found significant monthly and inter‐annual variation in defaecation rates with implications for their predictability and forest elephant surveys. In particular, our results show that mean defaecation rates are higher for the wettest period of the year than the relatively dry months.     

Thresholds and Time Lags in Effects of Energy Development on Greater Sage-Grouse Populations

ABSTRACT Rapid expansion of energy development in some portions of the Intermountain West, USA, has prompted concern regarding impacts to declining greater sage-grouse (Centrocercus urophasianus) populations. We used retrospective analyses of public data to explicitly investigate potential thresholds in the relationship between lek attendance by male greater sage-grouse, the presence of oil or gas wells near leks (surface occupancy), and landscape-level density of well pads. We used generalized linear models and generalized estimating equations to analyze data on peak male attendance at 704 leks over 12 years in Wyoming, USA. Within this framework we also tested for time-lag effects between development activity and changes in lek attendance. Surface occupancy of oil or gas wells adjacent to leks was negatively associated with male lek attendance in 5 of 7 study areas. For example, leks that had ≥ 1 oil or gas well within a 0.4-km (0.25-mile) radius encircling the lek had 35–91% fewer attending males than leks with no well within this radius. In 2 of these 5 study areas, negative effects of well surface occupancy were present out to 4.8 km, the largest radius we investigated. Declining lek attendance was also associated with a higher landscape-level density of well pads; lek attendance at well-pad densities of 1.54 well pads/km² (4 well pads/mile²) ranged from 13% to 74% lower than attendance at unimpacted leks (leks with zero well pads within 8.5 km). Lek attendance at a well-pad density of 3.09 well pads/km² (8 well pads/mile²) ranged from 77% to 79% lower than attendance at leks with no well pad within 8.5 km. Further, our analysis of time-lag effects suggested that there is a delay of 2–10 years between activity associated with energy development and its measurable effects on lek attendance. These results offer new information for consideration by land managers on spatial and temporal associations between human activity and lek attendance in sage-grouse, and suggest that regional variation is an important consideration in refining existing management strategies.     

Population size estimation of an Asian elephant population in eastern Cambodia through non-invasive mark-recapture sampling

The Asian elephant is a flagship species for conservation in tropical Asia, but reliable population estimates are available only from a few populations. This is because the species can be elusive and occurs at low densities in dense habitat over a large part of its range. Phnom Prich Wildlife Sanctuary in the Eastern Plains, Cambodia, which is part of one of the largest protected area complexes in South-East Asia, is one such habitat that had not been systematically censused for elephants. We, therefore, used fecal-DNA based capture-mark-recapture sampling to estimate the population size for establishing a monitoring baseline. Five sampling sessions targeted all areas in and adjacent to Phnom Prich Wildlife Sanctuary believed to be used by elephants. Fresh dung was collected as the source of DNA and genotyping was carried out based on nine microsatellite loci. The 224 samples collected yielded 78 unique genotypes. Using model averaging of closed population capture-mark-recapture models, the elephant population in Phnom Prich Wildlife Sanctuary was estimated to number 136 ± 18 (SE) individuals. Our results suggest that eastern Cambodia supports a regionally important Asian elephant population.     

The role of termites in the removal of elephant dung in the Tsavo (East) National Park Kenya

It has been noted that during the dry season the activity of coprophagous beetles on elephant dung decreases as that of termites increases. The action of termites on seventy plots provided with fresh (wet) dung, dry dung, water, dung liquid and con trols was investigated over a period of 38 days in August-September 1973. The rate at which termites attack dung is shown to differ significantly from other treatments. It is calculated that all the dung deposited during the period of the study can potentially be removed in 85 days. Measurements of termite foraging activity on the surface of the ground concludes that galleries (<5 days old) cover 0.96% of the surface.     

Does an aridity and trophic resource gradient drive patterns of dung beetle food selection across the Botswana Kalahari?

1. Aridity gradients are paralleled by both reductions in resources and decreased species richness of animals. Across the aridity gradient of the Botswana Kalahari, a reduction in mammal species richness leads to reduced density and diversity of dung types, accompanied by reduced dung beetle species richness. We investigated whether this gradient also drives changes in dung beetle food type association and specialisation owing to a loss of some dung types to the arid southwest. 2. Dung beetles were sampled from three study sites in each of the six study areas using 2 × 10 grids of pitfall traps baited with dung (pig, elephant, cattle, and sheep) or carrion (chicken livers). 3. Canonical correspondence analysis (CCA) showed that distributions of dung beetle species between bait types deviated significantly from random associations. 4. Central Kalahari assemblages were more specialist than those at the mesic and arid extremes of the gradient. 5. Patterns of selection and specialisation to bait types differed between mesic northeast and arid southwest study areas. There were specialist faunas on carrion and more generalist faunas on ruminant herbivore dung (cattle and sheep) in each region. However, specialist species associated with elephant dung in the northeast were replaced by a more generalist fauna in the southwest with an opposite trend on pig dung. 6. Reduced species richness and high species turnover from the mesic northeast to the arid southwest is paralleled by a shift in patterns of food association that may reflect changes in the diversity of food types, particularly the absence of elephant dung from the southwest.     

The influence of increasing population size and vegetation productivity on elephant distribution in the Kruger National Park

Decisions to reduce the impacts of large herbivores on biodiversity in protected areas are often based on controlling their numbers. However, numbers per se may not be the foremost consideration when managing impacts. This is because density‐related changes in distribution can also affect habitat utilization and hence, impact. In this study we tested whether changes in the distribution of African elephants are associated with increasing population size. We used spatially explicit count data collected during the dry seasons from 1998 to 2004 in South Africa's Kruger National Park. We did this at five spatial scales and in landscapes defined by vegetation, geology, climate and soils. We then investigated whether observed distributions and grid‐cell‐specific densities were associated with the remotely sensed Normalized Difference Vegetation Index (NDVI) as a measure of productivity and therefore food resource availability at the landscape scale. Consistent with density mediated changes, we found that elephant grid‐cell occupancy increased with population size, while grid‐cell‐specific density became less variable. In addition, the combined distribution of bull groups and breeding herds became less clumped with increasing population size. We further found that within landscapes elephants were present on grid‐cells with higher NDVI values, but that the influence of NDVI during the dry season on densities among landscapes may be weak. These results suggest that NDVI was more indicative of structural habitat choices such as woody vegetation than food availability per se. Our study highlights the need to consider factors other than population size alone when formulating management decisions to reduce large herbivore impacts on biodiversity in protected areas.     

Response of native ungulates to drought in semi‐arid Kenyan rangeland

The distribution and abundance of native ungulates were measured on commercially managed, semi‐arid rangeland in central Kenya over a 3‐year period that encompassed severe drought and above‐average rainfall. Native ungulate biomass density averaged 5282 kg km^?2 over the study and was dominated by elephant (Loxodonta africana), impala (Aepyceros melampus) and dik‐dik (Madoqua kirkii). Biomass density of domestic cattle (Bos taurus) averaged 2280 kg km^?2 during the study. Responses of native ungulates to severe drought were variable. Impala densities were similar to or greater than densities for similar habitat in protected areas, and varied from 12 to 16 km^?2 during and following the drought to 24–29 km^?2 following above‐average rainfall. Dik‐dik densities were also greater than densities reported for protected areas and were surprisingly stable throughout the study despite the wide annual fluctuations in rainfall. Elephant migrated out of the region during drought but were present at high densities (2.9–5.2 km^?2) during wet seasons, consistent with telemetry studies emphasizing the importance of Acacia bushland habitat on commercial rangelands for the migratory portion of the Laikipia–Samburu elephant population. Results show that substantial densities of native browsing and mixed‐feeding ungulates can occur on rangeland managed for commercial beef production and suggest that the capacity for ungulates to move over large spatial scales (>100 km²) and to shift distributions in response to locally variable thunderstorms may be important for sustaining these populations.