Nest Count Method Research Articles

Densities of Bornean orang-utans (Pongo pygmaeus morio) in heavily degraded forest and oil palm plantations in Sabah, Borneo.

The conversion of forest to agriculture continues to contribute to the loss and fragmentation of remaining orang‐utan habitat. There are still few published estimates of orang‐utan densities in these heavily modified agricultural areas to inform range‐wide population assessments and conservation strategies. In addition, little is known about what landscape features promote orang‐utan habitat use. Using indirect nest count methods, we implemented surveys and estimated population densities of the Northeast Bornean orang‐utan (Pongo pygmaeus morio) across the continuous logged forest and forest remnants in a recently salvage‐logged area and oil palm plantations in Sabah, Malaysian Borneo. We then assessed the influence of landscape features and forest structural metrics obtained from LiDAR data on estimates of orang‐utan density. Recent salvage logging appeared to have a little short‐term effect on orang‐utan density (2.35 ind/km 2), which remained similar to recovering logged forest nearby (2.32 ind/km 2). Orang‐utans were also present in remnant forest patches in oil palm plantations, but at significantly lower numbers (0.82 ind/km 2) than nearby logged forest and salvage‐logged areas. Densities were strongly influenced by variation in canopy height but were not associated with other potential covariates. Our findings suggest that orang‐utans currently exist, at least in the short‐term, within human‐modified landscapes, providing that remnant forest patches remain. We urge greater recognition of the role that these degraded habitats can have in supporting orang‐utan populations, and that future range‐wide analyses and conservation strategies better incorporate data from human‐modified landscapes.

Conservation of chimpanzeesPan troglodytes verusand other primates depends on forest patches in a West African savannah landscape

AbstractHabitat loss and fragmentation, hunting pressure, and human–wildlife conflict threaten the survival of primates across Africa. Particularly dramatic forest losses have occurred outside protected areas in the Guinean forest–savannah transition zone. Using the Boé region, Guinea-Bissau, as a case study, we investigated whether and how this rapidly humanized mosaic of wooded savannah, gallery forests and cropland could sustain viable primate populations. We conducted line transect surveys and reconnaissance (recce) walks to assess populations of one Critically Endangered (chimpanzeePan troglodytes verus), one Endangered (Temminck's red colobusPiliocolobus badius temminckii), one Vulnerable (king colobusColobus polykomos), and one Near Threatened (sooty mangabeyCercocebus atys) arboreal primates across a 104 km2section of Boé in the dry season of 2016. Using the standing crop nest count method we estimated a relatively high chimpanzee density (0.77 individuals per km2, 95% CI 0.45–1.34). An assessment of habitat selection showed that chimpanzees prefer semi-dense forest and fallow fields with remnant old trees for nesting, and locations close to rivers. The other primates studied occurred in extremely low densities and were largely restricted to gallery forests. Our results indicate a need for immediate action to ensure the long-term survival of the primate community in the human-dominated landscape of Boé. Our recommendations include action to maintain hunting pressure at a low level, restoring and protecting gallery forests, introducing incentives for farmers for forest protection and primate-friendly practices, and extending the conservation programme to all arboreal primates in the region.

Fluctuations of population density in Bornean orangutans (Pongo pygmaeus morio) related to fruit availability in the Danum Valley, Sabah, Malaysia: a 10-year record including two mast fruitings and three other peak fruitings.

We investigated the population density of Bornean orangutans (Pongo pygmaeus morio) and fruit availability for 10years (2005-2014), in primary lowland dipterocarp forests in the Danum Valley, Sabah, Malaysia. During the research period, two mast fruitings and three other peak fruiting events of different scales occurred in the study area. The orangutan population density, estimated every 2months by the marked nest count method, changed between 0.3 and 4.4ind/km2 and the mean population density was 1.3ind/km2±SE 0.1 (n=56). The population density increased markedly during mast and peak fruiting periods. A significant positive correlation was observed between the population density and fruit availability in the study period (Spearman, R=0.3, P<0.01, n=56). During non-fruiting periods, however, no significant correlation was observed between them. These results suggest that the spatial difference in fruit availability during mast and peak fruiting periods was larger than during non-fruiting periods, and many orangutans temporarily moved to the study site from the surrounding areas seeking fruit.

Chimpanzee research and conservation in Bossou and the Nimba Mountains: a long-term international collaborative effort in West Africa.

The Nimba Mountains are a West African Natural World Heritage site located in the range of the Guineo-equatorial evergreen rainforest, renowned for its rich biodiversity with a high level of endemism. In 1976, Yukimaru Sugiyama from Kyoto University initiated the long-term study of chimpanzees at Bossou, a Guinean village situated 5km from the northern foothills of Nimba. This Japanese initiative has provided key discoveries and insights on our closest living evolutionary relatives over the 40 past years, and has grown to become an international collaboration with a research focus extended to adjacent chimpanzee communities. The present paper describes a mid-term behavioral and ecological study on wild chimpanzees populating the southern slope of the Nimba Mountains, conducted in the framework of this collaborative project. It aimed to assess the status and ecological requirements of chimpanzees in order to formulate purpose-built actions for their conservation. We estimated a density of 0.46 chimpanzee per km(2) using nest count methods from line transects. We used logistic and Poisson regressions to investigate basic ecological characteristics of chimpanzees in relation to habitat composition and structure, topography and seasonality. We performed an in-depth analysis of their nesting and feeding behaviors, and identified important components of their diet; we also recorded their year-round ranging patterns. Our findings highlight the importance of old secondary forest and high-altitude habitats for these chimpanzees. We discuss the results in the light of other studies from the perspective of the conservation of the species and its natural habitat.

Density estimates and nesting-site selection in chimpanzees of the Nimba Mountains, Côte d'Ivoire, and Guinea.

We investigated nesting behavior of non habituated chimpanzees populating the Nimba Mountains to document their abundance and their criterions of nesting-site selection. During a 19-month study we walked 80 km of transects and recces each month, and recorded 764 nests (mean group size = 2.23 nests) along with characteristics of vegetation structure and composition, topography, and seasonality. Population density estimated with two nest count methods ranged between 0.14 and 0.65 chimpanzee/km(2) . These values are lower than previous estimates, emphasizing the necessity of protecting remaining wild ape populations. Chimpanzees built nests in 108 tree species out of 437 identified, but 2.3% of total species comprised 52% of nests. Despite they preferred nesting in trees of 25-29 cm DBH and at a mean height of 8.02 m, we recorded an important proportion of terrestrial nests (8.2%) that may reflect a cultural trait of Nimba chimpanzees. A logistic model of nest presence formulated as a function of 12 habitat variables revealed preference for gallery and mountain forests rather than lowland forest, and old-growth forest rather than secondary forests. They nested more frequently in the study area during the dry season (December-April). The highest probability of observing nests was at 770 m altitude, particularly in steep locations (mean ground declivity = 15.54%). Several of the reported nest characteristics combined with the existence of two geographically separated clusters of nest, suggest that the study area constitutes the non-overlapping peripheral areas of two distinct communities. This nest-based study led us to findings on the behavioral ecology of Nimba chimpanzees, which constitute crucial knowledge to implement efficient and purpose-built conservation.

Protection of the white-nest swiftlet Aerodramus fuciphagus in the Andaman Islands, India: an assessment

AbstractInternational trade of swiftlet nests has affected wild populations of edible-nest swiftlets throughout their range. The white-nest swiftlet Aerodramus fuciphagus of the Andaman and Nicobar Islands lost 80% of its population in the 1990s. Conservation efforts for the species were initiated in 2000, with the active involvement of former nest collectors. To measure the efficacy of protection measures we collected data on the swiftlet, using the nest count method. We monitored annual breeding populations in 28 protected caves on Chalis-ek and one on Interview Island during 2000–2008, and in 168 unprotected caves on Baratang and Interview Islands during February–April 2008. The swiftlet population in protected caves increased by 39%, whereas it declined by 74% in unprotected caves. Nearly 61% of the 152 caves on Baratang Island were abandoned by the swiftlet during 1997–2008. This study highlights the importance of extending protection to the unprotected caves on the Andaman and Nicobar Islands.

Population status of Pan troglodytes verus in Lagoas de Cufada Natural Park, Guinea-Bissau.

The western chimpanzee, Pan troglodytes verus, has been classified as Endangered on the IUCN Red List since 1988. Intensive agriculture, commercial plantations, logging, and mining have eliminated or degraded the habitats suitable for P. t. verus over a large part of its range. In this study we assessed the effect of land-use change on the population size and density of chimpanzees at Lagoas de Cufada Natural Park (LCNP), Guinea-Bissau. We further explored chimpanzee distribution in relation to landscape-level proxies of human disturbance. Nest count and distance-sampling methods were employed along 11 systematically placed linear transects in 2010 and 2011. Estimated nest decay rate was 293.9 days (%CV = 58.8). Based on this estimate of decay time and using the Standing-Crop Nest Count Method, we obtained a habitat-weighted average chimpanzee density estimate for 2011 of 0.22 nest building chimpanzees/km2 (95% CI 0.08–0.62), corresponding to 137 (95% CI 51.0–390.0) chimpanzees for LCNP. Human disturbance had a negative influence on chimpanzee distribution as nests were built farther away from human settlements, roads, and rivers than if they were randomly distributed, coinciding with the distribution of the remaining patches of dense canopy forest. We conclude that the continuous disappearance of suitable habitat (e.g. the replacement of LCNP's dense forests by monocultures of cashew plantations) may be compromising the future of one of the most threatened Guinean coastal chimpanzee populations. We discuss strategies to ensure long-term conservation in this important refuge for this chimpanzee subspecies at its westernmost margin of geographic distribution.

Estimating Orangutan Densities Using the Standing Crop and Marked Nest Count Methods: Lessons Learned for Conservation

ABSTRACTReliable estimates of great ape abundance are needed to assess distribution, monitor population status, evaluate conservation tactics, and identify priority populations for conservation. Rather than using direct counts, surveyors often count ape nests. The standing crop nest count (SCNC) method converts the standing stock of nests into animal densities using a set of parameters, including nest decay rate. Nest decay rates vary greatly over space and time, and it takes months to calculate a site‐specific value. The marked nest count (MNC) method circumvents this issue and only counts new nests produced during a defined period. We compared orangutan densities calculated by the two methods using data from studies in Sumatra and Kalimantan, Indonesia. We show how animal densities calculated using nest counts should be cautiously interpreted when used to make decisions about management or budget allocation. Even with site‐specific decay rates, short studies using the SCNC method may not accurately reflect the current population unless conducted at a scale sufficient to include wide‐ranging orangutan movement. Density estimates from short studies using the MNC method were affected by small sample sizes and by orangutan movement. To produce reliable results, the MNC method may require a similar amount of effort as the SCNC method. We suggest a reduced reliance on the traditional line transect surveys in favor of feasible alternative methods when absolute abundance numbers are not necessary or when site‐specific nest decay rates are not known. Given funding constraints, aerial surveys, reconnaissance walks, and interview techniques may be more cost‐effective means of accomplishing some survey goals.

Using Simulation Models to Evaluate Ape Nest Survey Techniques

BackgroundConservationists frequently use nest count surveys to estimate great ape population densities, yet the accuracy and precision of the resulting estimates are difficult to assess.Methodology/Principal FindingsWe used mathematical simulations to model nest building behavior in an orangutan population to compare the quality of the population size estimates produced by two of the commonly used nest count methods, the ‘marked recount method’ and the ‘matrix method.’ We found that when observers missed even small proportions of nests in the first survey, the marked recount method produced large overestimates of the population size. Regardless of observer reliability, the matrix method produced substantial overestimates of the population size when surveying effort was low. With high observer reliability, both methods required surveying approximately 0.26% of the study area (0.26 km2 out of 100 km2 in this simulation) to achieve an accurate estimate of population size; at or above this sampling effort both methods produced estimates within 33% of the true population size 50% of the time. Both methods showed diminishing returns at survey efforts above 0.26% of the study area. The use of published nest decay estimates derived from other sites resulted in widely varying population size estimates that spanned nearly an entire order of magnitude. The marked recount method proved much better at detecting population declines, detecting 5% declines nearly 80% of the time even in the first year of decline.Conclusions/SignificanceThese results highlight the fact that neither nest surveying method produces highly reliable population size estimates with any reasonable surveying effort, though either method could be used to obtain a gross population size estimate in an area. Conservation managers should determine if the quality of these estimates are worth the money and effort required to produce them, and should generally limit surveying effort to 0.26% of the study area, unless specific management goals require more intensive sampling. Using site- and time- specific nest decay rates (or the marked recount method) are essential for accurate population size estimation. Marked recount survey methods with sufficient sampling effort hold promise for detecting population declines.

Monitoring population decline: can transect surveys detect the impact of the Ebola virus on apes?

In 2004 the Ebola virus caused a drastic decline in western gorilla Gorilla gorilla abundance at Lokoue Bai, a clearing in Odzala National Park, Republic of Congo. This decline was detected by observations of gorillas visiting the clearing. We confirm that the sympatric chimpanzee Pan troglodytes population was also affected by the Ebola outbreak, and test whether the decline in the ape population would have been detected with line-transect surveys, the most commonly used wildlife monitoring methodology in Central Africa. We also evaluate the potential of transect surveys for describing the extent and pinpointing the timing of drastic population declines when this information is not known from other evidence. Both nest survey using the marked nest count method and standing stock survey of other signs of ape presence (dung, feeding remains, prints) were able to detect the decline. However, only nests and dung were reliable indices for estimating the magnitude of the decline and accurately pinpointing the timing. It was necessary to pool data across many survey replicates because of small samples sizes. Our results suggest that transects methods are able to detect drastic changes in ape abundance but that large sample sizes are necessary to achieve adequate statistical power. We therefore recommend that those intending to use transect methods as tools for monitoring large forest mammals evaluate in advance how much effort will be necessary to detect meaningful changes in animal abundance. © 2008 Fauna & Flora International.

Censusing chimpanzees in the Budongo Forest, Uganda

It is difficult to make valid comparisons of chimpanzee densities among sites because observers calculate them using different methods. We argue that nest count estimates of density are preferable to densities from home range estimates because of the problems of defining home range. There are many problems associated with nest count methods, some of which have not been addressed in previous studies. In 1992, we censused chimpanzees in the Budongo Forest using three methods;the standing crop nest count (SCNC), the marked nest count (MNC), and visual sightings of the animals (VS). Each method is based on standard line transect techniques. Of 96 nests monitored for decay rate,those constructed in the dry seasons decayed faster than those in the wet seasons. All- day follows of individual chimpanzees and observations of nesting chimpanzees at dusk showed that about 15.8% of night nests were reused,17.5% of the population did not build nests, and 18.8% of nests were first constructed as day nests. Given the variability in nest decay rates, we argue that MNC is a better method than SCNC because it avoids having to calculate decay rates.

Red imported fire ants (Hymenoptera: Formicidae): population dynamics following treatment with insecticidal baits.

Evaluation of Solenopsis invicta Buren populations following insecticidal bait treatments is usually made on the basis of presence or absence of active nests. An alternative method is described in which population densities are based on total worker ants per hectare. Using these two methods, we found that there was essentially no difference in population levels of treated and untreated plots 27 to 36 months after application of two baits. In a more detailed study in which imported fire ant colonies were monitored for 156 weeks, the number of ant colonies had increased 327% after 44 weeks; however, the total number of ants in these same colonies was still 84% below pretreatment numbers. These data reflect the great difference in size of mature pretreatment colonies and small incipient posttreatment colonies. Based on the total ant population method, total ant numbers remained below that in the check area for 2 years. Thus, effective control of the pest extended well beyond that indicated by the nest count method.