Methodological problems related to spotlight count as a census technique for Lepus europaeus in an alpine environment

Population estimations are necessary for effective conservation management. In Italy, brown hare populations are commonly censused by spotlighting, but this method does not seem to suit an alpine environment due to its vegetational and orographical complexity. The aim of this study is to evaluate the critical aspects related to spotlight census method in an alpine environment. Spotlight was carried out along two transects of a typical alpine environment. Observed animals were used to define density (number of animal seen/100 ha) and method precision (coefficient of variation (CV) applied to monthly repeated observations). Animal detectability was evaluated using half-normal function with cosine expansion (Distance 5.0®). Animal observability was evaluated by analyzing density estimates related to habitat conformation (unseen areas or full visibility). The exact surface surveyed by spotlighting was evaluated, defining the observation spotlight beam range (OTA) and the land useful sighting (LUS). In the end, LUS was classified in three patches according to hare presence: no hares, occasional hare presence, and constant hare presence. To evaluate habitat influence onto CV, we used a bootstrap simulation. The results show that spotlighting alone is not the most suitable method to apply in the alpine environment because habitat structure highly influences census results. Recommendations to improve spotlight surveys for monitoring European brown hare populations are given.     

Visual census methods underestimate density and diversity of cryptic reef fishes

The diversity and density of small, benthic reef fishes were estimated using visual census and enclosed rotenone stations. Visual census underestimated the number of species present and the density of common species by up to 91%.     

Vertical distribution of wild Yakushima macaques (Macaca fuscata yakui) in the western area of Yakushima Island, Japan: Preliminary report

A census of wild Yakushima macaques (Macaca fuscata yakui) was carried out in a 23-km² area of the western coast of Yakushima Island, Japan. We analyzed the census data to investigate changes in monkey distribution associated with the vertical distribution of vegetation. In the lowland coastal zone of 0–300 m above sea level (a.s.l.), 4.8 troops and 62.4–99.8 monkeys are estimated to have existed per km². In the mountainside zones of 300–900 m a.s.l., the troop density decreased to 1.3–1.6 troops/km². Since there was no difference in size between the coastal and mountainside troops, population density should decrease with altitude to about 30–36 monkeys per km². On the other hand, 2.4 troops and about 36 monkeys were estimated to have inhabited per km² in the mountain summit zone of 900–1,323 m a.s.l. Nature Conservation College     

Troop size and human-modified habitat affect the ranging patterns of a chacma baboon population in the cape peninsula, South Africa

Differences in group size and habitat use are frequently used to explain the extensive variability in ranging patterns found across the primate order. However, with few exceptions, our understanding of primate ranging patterns stems from studies of single groups and both intra- and inter-specific meta-analyses. Studies with many groups and those that incorporate whole populations are rare but important for testing socioecological theory in primates. We quantify the ranging patterns of nine chacma baboon troops in a single population and use Spearman rank correlations and generalized linear mixed models to analyze the effects of troop size and human-modified habitat (a proxy for good quality habitat) on home range size, density (individuals/km(2) ), and daily path length. Intrapopulation variation in home range sizes (1.5-37.7 km(2) ), densities (1.3-12.1 baboons/km(2) ), and daily path lengths (1.80-6.61 km) was so vast that values were comparable to those of baboons inhabiting the climatic extremes of their current distribution. Both troop size and human-modified habitat had an effect on ranging patterns. Larger troops had larger home ranges and longer daily path lengths, while troops that spent more time in human-modified habitat had shorter daily path lengths. We found no effect of human-modified habitat on home range size or density. These results held when we controlled for the effects of both a single large outlier troop living exclusively in human-modified habitat and baboon monitors on our spatial variables. Our findings confirm the ability of baboons, as behaviorally adaptable dietary generalists, to not only survive but also to thrive in human-modified habitats with adjustments to their ranging patterns in accordance with current theory. Our findings also caution that studies focused on only a small sample of groups within a population of adaptable and generalist primate species may underestimate the variability in their respective localities.     

Social interactions among adult male langurs (Presbytis entellus) at Rajaji Wildlife Sanctuary

A population of langurs (Presbytis entellus)at the Rajaji Wildlife Sanctuary in northern India was investigated for 1820 hr throughout a 10-month period in 1978. Data were collected from four bisexual troops and the adult males that ranged outside of bisexual troops. Most (60%) of the observation hours occurred with a main study troop from which social and ecological data were collected. The langur population at Rajaji shows pronounced birth and mating seasons. The population density is high (ca. 80/km ²), with about 75% of the adult males living outside of bisexual troops, which typically are large and multimale. Males outside of bisexual troops occur in small all-male bands or as isolates. Relations between bisexual troops and all-male bands are characterized by relatively low levels of aggression, and members of all-male bands are able to associate with bisexual troops for prolonged periods during the mating season. As a result of these associations, nontroop males are about as successful as troop males in achieving reproductive access to troop females. These associations between bisexual troops and all-male bands occurred with a minimal amount of agonistic behavior and without mortality or injury to troop females or immatures.     

Demography of Lemur catta at Berenty Reserve,Madagascar: Effects of Troop Size,Habitat and Rainfall

We censused Lemur catta within a 1 km² study area at Berenty Reserve, Madagascar, during the September–October birth season for 19 years between 1963 and 2000, a total of 290 troop counts (266 with age and sex). The non-infant population was 155 in 1972–5, fell to 105 in 1985, and rose to a maximum of 282 in 1997, while troops increased from 12 in 1972–1985 up to 25 in 1998–2000. Local density varies between habitat types from 1 per ha to ca. 6 per ha. Troops fission at ca. 15–25 individuals, or 6–10 females. Adult sex ratio has no apparent correlation with fissions, birth rate or survival. Birth rate falls steeply with number of adult females, from 80–100% in 2-female troops to about 50% in 8–10 female troops. The penalty for large troop size is greater in the dense, rich areas, but nonetheless troops there are also larger. One-year-survival does not vary with troop size, and is lower in the sparse, dry zone. Troop size is too large for optimal birth rate, but fissioning to much lower size might make troops too small for optimal adult survival, given the intense intertroop competition. This reflects Sibley's (1983) conjecture that troop sizes may not reach stable optima. Rainfall per lemur-year (beginning Oct 1) varied from 265 to 894 mm. Drought followed by rain can eliminate >90% of a cohort, especially in the dryest zone. Possibly this results from fruit failure in years following drought. It is unknown whether food supplementation of some Berenty troops is dangerous for the forest, or helpful for an isolated and vulnerable ring-tailed lemur population.     

Population Structure and Ranging Patterns of <Emphasis Type="Italic">Rhinopithecus roxellana</Emphasis> in Zhouzhi National Nature Reserve,Shaanxi, China

We describe the population structure and ranging patterns of a troop of Sichuan snub-nosed monkeys (Rhinopithecus roxellana) based on a study conducted between November 2002 and November 2003 in Zhouzhi National Nature Reserve, Shaanxi Province, China. The troop comprised several 1-male units and an all-male unit. Opportunistic censuses revealed that there were ≥112 individuals in the troop. The adult sex ratio (male vs. female) was 1:3.7. The ratios of adults to immatures and infants to adult females were 1:0.7 and 1:2, respectively. Via a grid system, we estimated the home range of the troop to be 18.3 km², of which 7.4 km² was the core area. The subjects exhibited distinct seasonal ranging patterns. Their movement across the home range was extensive in spring and restricted in autumn. In addition, reuse of quadrats was highest in winter and lowest in spring in comparison with other seasons. The daily path length (DPL) varied from .75 to 5 km, with a mean of 2.1 km. Seasonal analysis showed that DPL is significantly shorter in winter than in spring or summer; however, there is no significant difference between the DPLs of spring and summer or those of spring and autumn. The monkeys occupied elevations 1500–2600 m above sea level; the annual mean of altitudinal range is 2137 m. Contrary to early studies that reported Rhinopithecus roxellana migrates to lower elevations in winter, we found no evidence supporting a seasonal altitudinal shift. Using the highest troop count and home range estimate, and considering the extent of range overlap between neighboring troops, we calculated the population density and biomass of Rhinopithecus roxellana to be 7.2 individuals/km² and 68.3 kg/km², respectively. The temporal and spatial distribution of food resources may be the most important determinant of ranging behavior in Rhinopithecus roxellana, though understanding the relationship between resource distribution and seasonal range use may require further investigation.     

Topography-specific emergence of fungal fruiting bodies in warm temperate evergreen broad-leaved forests on Yakushima Island,Japan

We conducted line route censuses of fungal fruiting bodies from August to September in 2005 and 2006 along ridges and valleys and compared the differences in the encounter rates of fungal fruiting bodies (= fruiting bodies seen per census kilometer) between types of topography and between fungal functional groups (i.e., ectomycorrhizal and saprobic fungi) in warm temperate evergreen broad-leaved forests on Yakushima Island, Japan. We found 251 fungal fruiting bodies (26 families, 50 genera, and 65 species) in total, including 51 bodies from Tricholomataceae, 41 from Russulaceae, 25 from Boletaceae, and 19 from Amanitaceae. The encounter rate of ectomycorrhizal fungi was greater at the ridge route (26.7 unit/km) than at the valley route (8.7 unit/km) and that of saprobic fungi was greater at the valley route (25.0 unit/km) than at the ridge route (12.5 unit/km). In addition, we conducted 7-year intermittent sampling and identified 40 families, 96 genera, and 142 species. The topography-specific emergence pattern of the intermittent sampling method was similar to that of the line census method. The fungal species composition in this study was possibly affected by a topographic gradient for both fungal functional groups through soil moisture, nutrient availability, and host tree distribution.     

紫红笛鲷幼鱼对集群密度和投饵定额的摄食反应

研究了紫红笛鲷(Lutjanus argentimaculatus)幼鱼在不同集群密度和投饵定额下的摄食反应.实验设7个不同的集群组(1、2、3、4、8、12、16尾/组),每个集群组又分成7个不同的投饵定额组(18.4×10-227.6×10-2、36.8×10-2、46.0 × 10-2、55.2×10-2、64.4×10-2、73.6×10-2g/组),通过测定摄食量观测幼鱼的摄食反应.在定额投饵的情况下,紫红笛鲷每尾幼鱼的一次平均摄食量随群体密度的增大呈先增加、超过一定密度后下降的趋势.1尾组与其他组差异极显著(P＜0.01),其组平均一次摄食量最低.当集群密度不变时,紫红笛鲷幼鱼一次平均摄食量随投饵定额的增大而增加,然后减小.随着集群密度增大,不同密度群体的最大摄食量向投饵定额增加的方向移动;而随着投饵定额增加,不同定额组的最大摄食量相对集中在2～8尾的群体中.结果表明,集群密度、投饵定额以及两者的交互作用对紫红笛鲷幼鱼的一次摄食量有极显著影响,群居的互利性和竞争性作用效果明显.     

Survey and census of howler monkeys (Alouatta palliata) in the rain forest of “Los Tuxtlas,” Veracruz,Mexico

Howler monkey troops were censused at the biological reserve “Los Tuxtlas” in Veracruz, Mexico. The reserve includes 700 ha of rain forest. Twenty howler monkeys were also trapped, measured, marked, and released. Censuses were conducted for a period of 26 months, and they indicated the existence of 17 troops. The mean troop size was 9.12 (SD ± 2.93), and mean troop composition was 3.0 adult males, 4.12 females, 1.56 juveniles, and 1.54 infants. Ecological density was 0.23 howlers/ha or 23.29 howlers/km². The male to female ratio was 1:1.37. No discrete seasonality in births was noted. Howler monkeys in this locality inhabit the northernmost limit of the neotropical rain forest. The population parameters fall within those reported for Alouatta palliata at other sites.     

The variable social organization of hanuman langurs(Presbytis entellus), infanticide,and the monopolization of females

Data from 24 wild populations of hanuman langurs (Presbytis entellus)in south Asia are used to test hypotheses seeking to explain variation in troop structure and the incidence of infanticide. The occurrence of infanticide is associated with a one-male troop structure and not with a high density. The density, predation, and economic-advantage hypotheses, as explanations for the occurrence of one-male and multimale troops, are not supported by the review. However, the monopolization hypothesis is not contradicted; the number of adult males per troop is significantly correlated with troop size and with the number of adult females per troop. Therefore it is suggested that a one-male troop structure will arise if a male is able to monopolize a group of females, a multimale troop if he cannot. One-male troops may predispose to infanticide because of high variance in male mating success and high intermale competition between groups rather than within troops. If female dispersion determines troop structure, it is speculated that females could manipulate males to form a multimale society if the advantages in terms of infant survival and intertroop conflict exceeded the costs in terms of not producing infanticidal “sexy sons.”     

Comparative analysis of visual census techniques for highly mobile,reef-associated piscivores (Carangidae)

Synopsis Visual census techniques applicable to coral reef-associated fishes are reviewed and the results of field tests using six (three transect-based and three point-based) to estimate the density of carangids at Carter Reef, Great Barrier Reef, are presented. Data are analyzed with respect to the effects of observers on fishes seen, observer biasses, precision of the estimates and, as far as possible, accuracy of the estimates. Transects generate estimates of population density and structure different from those of point-based estimates. Various point-based census methods, however, generate density estimates consistent with one another and are generally more precise than transect-based methods. The results of the field study obviously cannot be generalized to other quite different types of reef fishes. The problems we encountered and a review of the techniques used to census reef fishes visually in the past, however, suggest that: (1) interval counts, such as Rapid Visual Census techniques, are likely to be inaccurate and difficult to compare; (2) for species with high probabilities of detection, instantaneous area counts appear to be the most effective way to estimate densities, whereas cryptic species are best censused using instantaneous variable distance point counts, and (3) strip transects may often be less efficient than line transects, due to inconstant levels of subject detectability.     

Differential detectability of primates between primary and selectively logged habitats and implications for population surveys

Much information has been published concerning the accurary of various techniques commonly used for censusing primates. The sources of bias may vary according to the technique used. Accuracy may depend on population density as well as on differential visibility and hence detectability between areas. This paper provides evidence that primates may alter their behavior between areas of primary and selectively logged habitat, which in turn could affect census results. Adoption of cryptic behavior, changes in behavioral profile, and reduction in calling rates reduce the detectability of certain species. Increases in the frequency of subgrouping or in group dispersion may introduce a danger of overestimation of other species, unless differences in the size of foraging units are taken into account.     

ICE-BASED CENSUS OF BOWHEAD WHALES MIGRATING PAST POINT BARROW, ALASKA, 1978-1983

Bowhead whale ( Balaena mysticetus ) census data obtained during the northward spring migration are summarized for 1978–1983. Population size estimates are derived from counts made by observers standing on the seaward edge of shorefast ice in the vicinity of Point Barrow, Alaska, from mid-April to early June. The research design utilized two counting stations: South Perch, the primary counting station, and North Perch, used to determine the number of whales missed by South Perch observers. The percentage missed is estimated for each visibility category and used here to correct the census counts. Each season's population estimate is calculated as the sum of the number of trials of several independent multinomial distributions representing different visibility conditions. Corrections are applied for unwatched hours and hours with inferior visibility. A mean estimate of the number of whales passing within view of the census station was computed as 3,674 ± 299. This estimate was based on data collected in 1978, 1981, 1982, and 1983, years with the least apparent biases. Aerial survey data provide estimates of the proportion of whales passing at various distances seaward of the census sites as follows: 0.58 from the ice edge to 2 km, 0.76 to 3 km, and 0.80 to 4 km. Correcting for whales too far offshore to be seen by the ice-based observers results in a population estimate of over 4,200 bowheads.     

Censusing primates by transect in a forest of known primate density

A series of four transect or strip censuses of primates was carried out in a forest in eastern Colombia where the absolute density of the three diurnal species had been previously calculated during long-term studies. The diurnal species were Alouatta seniculus, Callicebus torquatus,and Cebus apella.Techniques were identical, except for a few variables tested for their effect on the experimental results;these included three different types of detection distances. Variable results were obtained for the two species having the smallest home ranges (A. seniculusand C. torquatus)with the most consistently accurate densities being calculated using the drop in the frequency distribution of sighting distances as a measure of the detection distance. Grossly inflated results were obtained for almost all calculations of C. apelladensity. The stimulus leading to the detection of particular primate groups was usually their vocalizations. Counts of recognized group members were inaccurate and short of the actual number of individuals in each group. Problems of censusing primates are discussed and some recommendations are made with respect to the use of the transect census method.     

The social organization of forest hanuman langurs(Presbytis entellus)

The social organization of hanuman langurs (Presbytis entellus;Colobinae) was studied in Kanha Tiger Reserve, Central Indian Highlands, for 2300 hr (1980–1985), in a mosaic of moist deciduous forest and anthropogenic meadow. The langur population density was 46.15/km ² and the mean troop and band sizes were 21.7 and 14.0, respectively. Of 14 troops, 13 were one-male and 1 was trimale. The population adult sex ratio was 1:2.5. The majority of female sexual solicitations was directed toward the harem male. The birth season was December to May, with an estimated gestation of 171–224 days. A review of langur reproductive seasonality suggests that breeding throughout the year is confined to those populations able to exploit human food sources. Mortality during the first year of life was 40%, including infanticide. A significant positive correlation was found between the age of an infant at death or disappearance and the mother’s subsequent interbirth interval. Five cases of social change are described, including female transfer, one-male to multimale change, troop formation, and gradual and rapid replacement of troop males. Takeover-associated infant killing by band males, in an undisturbed moderate-density population, supported the sexual-selection/infanticide hypothesis but not the social-pathology hypothesis. However, it could not be directly confirmed that an invading infanticidal male gains a reproductive advantage. The male tenure of harems was estimated to be 45 months.     

On the determinants of census area: implications for mammalian macroecological patterns

The aim of this study was to examine the effects of various biological factors such as body mass, trophic level, climate and geography on census area in terrestrial mammals. We also examine the effects of census area on the population density–body mass relationship. The geographic areas covered in this study include most major terrestrial biomes including taïga, desert, savanna, grassland, tropical dry forest, temperate dry forest, tropical rain forest and temperate rain forest. An extensive literature search was conducted and we compiled data on census area and body mass from 377 mammalian populations and 59 communities. Statistical analyses include linear regression, Kruskal–Wallis analysis of variance, LOWESS, and multiple regression. Overall, the regression between log census area (A) and log body mass (M) yielded a slope of 0.710, which did not differ significantly from 0.75, but it was significantly different from 1.0. The analyses also showed that the log A–log M relationship is constrained within a well‐defined space in a similar fashion to the home range–body mass relationship. When mammals were separated into trophic groups, regression lines differed significantly in their intercepts, but not in slopes. At the community level, the census area was particularly affected by the population with the largest body mass within the community. Both the number of species and number of taxa encompassed by the community were found to be correlated positively with log A (r = 0.26, P = 0.0464 and r = 0.27, P = 0.0398, respectively). Sampling of mammalian species is not usually random. Not only is census area significantly associated with the technique used to sample a given species, but it is also influenced by biological factors that have been shown previously to influence population density. Striking similarities were found between the census area–body mass relationship and the home range–body mass relationship, suggesting that investigators may sample mammalian populations over areas that actually reflect the use of space of their focal species.     

Changes in dominance rank and division of a wild Japanese monkey troop in Arashiyama

This article forms the second report on the Arashiyama troop of Japanese monkeys and concerns a troop division which took place in June, 1966, and various problems of rank and consanguinity which accelerated the division. (1) The hypothesis advanced in the first report has been verified; (2) at the time of troop division, several consanguineal groups formed one unit; (3) among 16 consanguineal groups, those from 1st to 7th in rank joined the A troop, while those from 8th to 16th joined the B troop; (4) dominance relation between the two division troops was B troop>A troop, reflecting the former ranking between the leader males of the two troops; (5) shifting of monkeys from one troop to the other after division occurred frequently, but males began to make their own movements when they attained 4 or 5 years of age and rarely moved together with their mothers or other consanguineous-relatives; (6) monkeys which were continuously in the same troop after division almost always obtained higher ranks than did monkeys who frequently shifted from one troop to the other; (7) after division, some males joined neither of the two division troops but formed a group, a so-called all-male group or male party, and moved about independently.     

Assessment of the release of rehabilitated vervet monkeys into the Ntendeka Wilderness Area, KwaZulu-Natal, South Africa: a case study

In South Africa, vervet monkeys (Chlorocebus aethiops) are frequently persecuted, resulting in large numbers of injured and/or orphaned animals. Rehabilitation centres aim to care for these monkeys and ultimately return them to the wild whenever possible. However, it is unknown whether rehabilitation is successful in its goal of creating wild-living, independent, self-sustaining troops due to limited published research in this area. This study describes the release and subsequent fate of a troop of rehabilitated vervet monkeys over a 6-month period. A troop of 16 monkeys was released into the Ntendeka Wilderness Area, a protected part of Ngome Forest, by the WATCH (Wild Animal Trauma Centre and Haven) rehabilitation centre in KwaZulu-Natal, South Africa. Monitoring data were evaluated with regard to survival, mortality, suitability of the release site, breeding, condition, troop composition, behaviour, group dynamics, ranging patterns and the effectiveness of monitoring tools. The release was considered to be a partial success in that the troop exhibited behaviour, group dynamics and ranging patterns similar to wild conspecifics. However, the survival rate was low and the troop was judged to be non-self-sustaining. The main problems identified were the limited lifetimes of radio collars, which resulted in missing animals and caused monitoring to be cut short, illegal hunting activities, predation and a small troop size with few adults. The authors recommend improvements that may increase success, such as retaining troops in release enclosures for longer periods, releasing a larger troop with more adults that more closely matches wild troop composition, selecting a release site at least 3 km from the nearest human settlement and the use of GPS collars to allow for a longer monitoring period encompassing all seasonal conditions. Furthermore, all primates for release should be medically screened so as to avoid potential negative impacts on wild populations.