Dung survey bias and elephant population estimates in southern Mozambique

We used dung surveys to estimate population size and extracted an age structure from boli diameters for the elephants living in the Maputo Elephant Reserve. Our estimate was based on published defecation rates, dung decay rates, distance-sampling techniques and 1,672 dung piles encountered on 204 line-transects. The reserve had at least 311 (95% CI: 198–490) elephants at a density of 0.60 (95% CI: 0.38–0.94) per km². However, observer bias reduced effective strip widths and inflated estimates and their confidence limits. The age structure extrapolated from dung measurements indicated few newborn calves compared with other populations. To detect population changes of 2–5% at 80% power, dung surveys should be carried out every second year for the next 20 years using 100 transects of at least 500 m each. Comparison with a 1995 dung survey suggests that the population is stable and that previous fears of a major population decline during the civil war have no foundation.     

Comparison of sample and total counts of elephant and buffalo in Masai Mara, Kenya

Both aerial transect sample counts and total counts of elephant and buffalo were conducted in the study area during the wet season. The results from the two counting methods were tested for significant difference. The test showed that the results were not significantly different for both the elephant ( P > 0.05) and buffalo ( P > 0.05).     

The problem of precision and trend detection posed by small elephant populations in West Africa

The precision of elephant estimates from aerial sample surveys and dung counts is inversely proportional to abundance. West African elephant populations are already small, and the power of a monitoring programme to detect changes in abundance diminishes as the population shrinks in size. Thus it will be difficult to evaluate the effects on elephant numbers of new management policies in West Africa. The same will be true of monitoring schemes for antelope and primate populations that are hunted for bushmeat. Elephant estimates from dung counts are more precise than those from aerial sample surveys, and changes in elephant numbers are more likely to be detected in the subregion by dung counts than by aerial sample surveys.     

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.     

Trends in populations of elephant and other large herbivores in Gonarezhou National Park,Zimbabwe, as revealed by sample aerial surveys

For 30 years, regular aerial surveys in Zimbabwean protected areas were funded, designed and executed primarily to estimate elephant numbers. Other large herbivores were recorded, even though some species were not easily seen from the air in savannah woodlands. Population estimates for species other than elephant provided indices of abundance that could be used to determine temporal trends in population size. This study tests for significant trends in the abundance of large herbivores in Gonarezhou National Park, assuming that data from aerial sample surveys designed for elephant also provide accurate estimates of real trends in the populations of other herbivores. For each species, the exponential rate of population change was calculated using weighted regression, with the variance of this rate based on the sampling variances of the population estimates. Significant population trends were detected for eight species. Before the 1992 drought, elephant number was held approximately constant by frequent culls, but afterwards, it increased at a mean annual rate of 6.2% (confidence limits 4.0% and 8.6%). Elephants in cow herds increased at 7.3%, significantly faster than elephants in bull herds (?0.5%). Buffalo, eland, kudu, nyala, waterbuck, wildebeest and zebra all increased in number, after population declines during the drought.     

Environmental implications of pollen spectra in bat droppings from southeastern Spain and potential for palaeoenvironmental reconstructions

Pollen was analysed from bat guano from nine caves in southeastern Spain and surface soils in their immediate surroundings. We compare the pollen spectra of 34 modern dung samples from the nine caves with one modern surface pollen sample from each cave. The contents suggest reasonable pollen diversity and richness, including anemophilous and zoophilous pollen types. Since the latter is usually under-represented in atmospheric pollen, the guano spectra therefore appear to reflect the vegetation more effectively than normal surface soil samples. Despite health hazards such as histoplasmosis, the difficulties of obtaining bat guano in deep caves and possible interpretational concerns relating to behaviour and feeding habits of different bat species, this material can be very useful in palaeoecological research provided that the dung was fossilized under favourable environmental conditions that allowed the preservation of pollen.     

A population size estimate of the finless porpoise,Neophocaena phocaenoides, from aerial sighting surveys in Ariake Sound and Tachibana Bay, Japan

We estimated the population size of the finless porpoise (Neophocaena phocaenoides) in Ariake Sound and Tachibana Bay of western Kyushu, southwestern Japan, from aerial sighting surveys using line transect methods. All 12 surveys were conducted from May 1993 to May 1994 (8 in Ariake Sound and 4 in Tachibana Bay). In addition to these, 14 surveys were also carried out to obtain information on porpoise occurrence in Tachibana Bay (5 surveys) and in neighboring Sumo Nada (5) and Yatsushiro Sound (4). In Ariake Sound, 225 porpoise groups (369 animals) were detected during all flights totalling 1,694.4 km. In Tachibana Bay, a total of 997.8 km was surveyed and 55 groups (290 animals) were sighted. However, no sightings were recorded in Sumo Nada (distance searched = 148.7 km) and Yatsushiro Sound (208.4 km). In Ariake Sound, few sightings were recorded from waters shallower than 5 m in depth. In Tachibana Bay all animals were detected from waters of less than 50 m depth. The population size was estimated as 1,983 animals in Ariake Sound (95% CI = 1,382-2,847), 1,110 in Tachibana Bay (95% CI = 642-1,920), and 3,093 in the 2 waters (1.3 individuals/km², 95% CI = 2,278-4,201).