Nest Counts Research Articles

Assessment of in situ nest decay rate for chimpanzees (Pan troglodytes ellioti Matschie, 1914) in Mbam-Djerem National Park, Cameroon: implications for long-term monitoring

Accurate assessment of great ape populations is a prerequisite for conservation planning. Indirect survey methods using nest and dung, and a set of conversion parameters related to nest decay rates, are increasingly used. Most surveys use the standing crop nest count (SCNC) method, whereby nests are counted along transects and the estimated nest density is converted into chimpanzee density using an often non-local nest decay rate. The use of non-local decay rate is thought to introduce substantial bias to ape population estimates given that nest decay rates vary with location, season, rainfall, nest shape, and tree species used. SCNC method has previously been applied in Mbam-Djerem National Park (MDNP) in Cameroon, for chimpanzee surveys using a non-local nest decay rate. This current study aimed to measure a local nest decay rate for MDNP and implications for chimpanzee population estimates in the MDNP. The mean nest decay rate estimated using a logistic regression analysis was 127 [95% CI (100–160)] days. Moreover, the results suggested that rainfall strongly influenced the nest decay rate over the early stage of the lifetime of the nests. The study confirms that estimates of chimpanzee density and abundance using non-local decay rates should be treated with caution. Our research emphasized the importance of using local nest decay rates and other survey methods which do not depend on decay rates to obtain more accurate estimates of chimpanzee densities in order to inform conservation strategies of these great apes in MDNP.

Density and distribution of western chimpanzees around a bauxite deposit in the Boé Sector, Guinea‐Bissau

The Boé sector in southeast Guinea-Bissau harbors a population of western chimpanzees (Pan troglodytes verus) that inhabits a mosaic of forest and savanna. The Boé sector contains a substantial bauxite deposit in a region called Ronde Hill, and there are plans for the construction of a mine, which may endanger the chimpanzee population. In 1-week survey in May 2013, we used the standing crop nest counts method to obtain the number of chimpanzee nests and from that estimate the density and abundance of chimpanzees. We carried out five 1-km line transects that covered the bauxite deposit and surrounding valleys. We used density surface modeling to analyze habitat preferences, then predicted chimpanzee nest density and distribution based on environmental variables. We found the projected location of the mine partially coincides with an area of high predicted abundances of chimpanzee nests and is surrounded by highly suitable areas for chimpanzees (northeast and southwest). We conclude the mine could have significant direct and indirect effects on this population of chimpanzees whose impacts must be carefully considered and properly mitigated if the mine is built.

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.

Changes to Sabah's orangutan population in recent times: 2002-2017.

The Bornean orangutan is critically endangered and monitoring its population is needed to inform effective conservation management. In this paper, we present results of 2014–17 aerial nest surveys of the major orangutan populations in Sabah and compare them with baseline data produced during surveys conducted in 2002–03 using similar methods. Our results show three important points: a) by increasing the survey effort (estimated at 15–25% cover), sparsely scattered orangutan sub-populations not recorded in the previous aerial surveys were located and the accuracy of the nest count estimates is expected to improve; b) large populations in the interior forests of Sabah, occupying sustainably managed logged and unlogged forests, have been stable over 15 years and are of vital importance for the species’ conservation; c) fragmented populations located in eastern Sabah, that are surrounded by extensive oil palm plantations, have declined at varying rates.

Numbers and distribution of the Great Cormorant in Iceland: Limitation at the regional and metapopulation level.

We studied a metapopulation of great cormorant (Phalacrocorax carbo) in Iceland, using complete aerial censuses of nests in 25 years during 1975–2015. Age composition was estimated in 1998–2014 by ground surveys in September and February. Brood size was estimated from aerial photographs in 2007–2015.Weather, food, breeding habitat, and density were considered as explanatory variables when examining numerical and distributional changes in the cormorant metapopulation.In 1975–1990 total nest numbers changed little, very low numbers about 1992 were followed by an annual increase of 3.5% in 1994–2015. Total nest numbers were positively correlated with estimates of spawning stocks of cod and saithe and inversely related to the subpolar gyre index (SPG‐I).During the increase in 1994–2015, average colony size at first increased and then declined. Habitat use also changed: the proportion of nests on small rocky islets (skerries) at first declined, from 69% to 44% in 1995–2003 and then increased again to about 58% in 2012–2014. Habitat changes were probably a response to changed patterns of human disturbance.Breeding density, as nests per km2 sea <20 m deep, was rather uniform among five defined regions in 1975–1996. Thereafter, densities became much higher in two sheltered regions with kelp forests and in one mostly exposed region. A second exposed region remained low and in the third nest numbers declined markedly. Thus, carrying capacity was higher in sheltered regions where cormorant breeding had historically been depressed by human disturbance.Brood size varied little among regions but declined with the years from about 2.5 to 1.8.The proportion of juveniles in September (fecundity) declined in 1998–2015 from over 0.4 to 0.3 and was inversely correlated with year and nest numbers, if outlier years were excluded, suggesting resource limitation. Survival of juvenile cormorants in September–February was estimated at 0.471 ± 0.066 SE. Commercial fish stocks and climate indices were not correlated with the proportion of juveniles.Annual survival of adults (breeding and nonbreeding) was estimated from nest counts and age composition 1999–2014, as 0.850 ± 0.026 SE and showed no trend in 1998–2014.We conclude that the metapopulation of cormorants in Iceland was resource‐limited at two levels: fecundity at the regional and winter survival at the total level.

Predator-prey dynamics of bald eagles and glaucous-winged gulls at Protection Island, Washington, USA.

Bald eagle (Haliaeetus leucocephalus) populations in North America rebounded in the latter part of the twentieth century, the result of tightened protection and outlawing of pesticides such as DDT. An unintended consequence of recovery may be a negative impact on seabirds. During the 1980s, few bald eagles disturbed a large glaucous‐winged gull (Larus glaucescens) colony on Protection Island, Washington, USA, in the Salish Sea. Breeding gull numbers in this colony rose nearly 50% during the 1980s and early 1990s. Beginning in the 1990s, a dramatic increase in bald eagle activity ensued within the colony, after which began a significant decline in gull numbers.To examine whether trends in the gull colony could be explained by eagle activity, we fit a Lotka–Volterra‐type predator–prey model to gull nest count data and Washington State eagle territory data collected in most years between 1980 and 2016. Both species were assumed to grow logistically in the absence of the other.The model fits the data with generalized R 2 = 0.82, supporting the hypothesis that gull dynamics were due largely to eagle population dynamics.Point estimates of the model parameters indicated approach to stable coexistence. Within the 95% confidence intervals for the parameters, however, 11.0% of bootstrapped parameter vectors predicted gull colony extinction.Our results suggest that the effects of bald eagle activity on the dynamics of a large gull colony were explained by a predator–prey relationship that included the possibility of coexistence but also the possibility of gull colony extinction. This study serves as a cautionary exploration of the future, not only for gulls on Protection Island, but for other seabirds in the Salish Sea. Managers should monitor numbers of nests in seabird colonies as well as eagle activity within colonies to document trends that may lead to colony extinction.

The Bornean orangutan (Pongo pygmaeus wurmbii) density in a logging concession of Hulu Belantikan, Central Kalimantan, Indonesia

Abstract. Sapari I, Perwitasari-Farajallah D, Utami Atmoko SS. 2019. The Bornean orangutan (Pongo pygmaeus wurmbii) density in a logging concession of Hulu Belantikan, Central Kalimantan, Indonesia. Biodiversitas 20: 878-883. The Bornean orangutan is currently categorized as a critically endangered species. It is found in natural forests in Borneo, where about 78% of the total population is found outside protected areas, of which 29% is in logging concessions. This study aimed to analyze the density of the orangutan population and the abundance of fruiting plants in a logging concession and Protection Forest (Hutan Lindung) in the Hulu Belantikan forests in Lamandau District, Central Kalimantan, Indonesia. Research and data collection was conducted between December 2013 to October 2014. Orangutan population density was calculated using line transect methodology based on nest counts. Abundance of fruit plants was calculated using the fruit trail method. The highest orangutan density, 4.8 individuals/km2, was found in Protection Forest; and the lowest density, 0.4 individuals/km2, was in [Sopanan] the 2013 logging block. Observations in the logging area indicated that selective logging could alter the structure and gap of the canopy and reduce the proportion of large trees. Changes in forest structure resulted in negative effects on the density of the orangutan population. The remaining degraded forests can still be a valuable resource for the orangutan. As long as the disturbance is not intensive, orangutans will retain access to the less disturbed forest nearby and to forests that are still connected to primary forests. The existence of Protection Forest and old logged-over forests around logging blocks are very important for conservation, providing refugia for orangutans and other species when logging occurs.

Improving population estimates of threatened spectacled eiders: correcting aerial counts for visibility bias

ESR Endangered Species Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials ESR 39:191-206 (2019) - DOI: https://doi.org/10.3354/esr00959 Improving population estimates of threatened spectacled eiders: correcting aerial counts for visibility bias Tyler L. Lewis1,3,*, Michael A. Swaim2, Joel A. Schmutz1, Julian B. Fischer2 1US Geological Survey, Alaska Science Center, Anchorage, Alaska 99508, USA 2US Fish and Wildlife Service, Migratory Bird Management, Anchorage, Alaska 99503, USA 3Present address: Alaska Department of Fish and Game, Division of Wildlife Conservation, Anchorage, Alaska 99518, USA *Corresponding author: tyler.lewis@alaska.gov ABSTRACT: Listed as ‘threatened’ under the US Endangered Species Act in 1993, the spectacled eider Somateria fischeri population in western Alaska, USA, has since rebounded, prompting an assessment of their suitability for delisting. This assessment, however, is limited by aerial-based population estimates that are incompletely corrected for unobserved eiders. Notably, aerial counts of eiders are corrected with a visibility correction factor (VCF), calculated as the ratio of ground-based nest counts to aerial pair counts, which disregards spatial variation in eider density. Accordingly, we (1) stratified our study area into zones of low, medium, and high eider density, (2) developed density-adjusted VCFs for each stratum, (3) evaluated the influence of several ecological factors on VCFs, and (4) estimated eider population size using our density-adjusted VCFs. For the low-density stratum, we estimated a VCF (± SE) of 1.35 ± 0.15, indicating that aerial counts of eider pairs closely matched ground counts of nests. In medium and high-density strata, VCFs increased to 2.46 ± 0.17 and 3.09 ± 0.19, respectively, suggesting that aerial detection decreased as eider densities increased. VCFs also increased for surveys that occurred late relative to nest initiation. Population estimates produced with our density-adjusted VCFs were 42% (5580 eiders) lower, on average, than those produced with the traditional VCF, which is currently used. Such large differences underscore the importance of accounting for density when correcting counts for incomplete detection, and, for threatened species such as spectacled eiders, may determine whether populations retain protected status. KEY WORDS: Spectacled eider · Somateria fischeri · Detection · Stratification · Abundance · US Endangered Species Act Full text in pdf format Supplementary material PreviousNextCite this article as: Lewis TL, Swaim MA, Schmutz JA, Fischer JB (2019) Improving population estimates of threatened spectacled eiders: correcting aerial counts for visibility bias. Endang Species Res 39:191-206. https://doi.org/10.3354/esr00959 Export citation Mail this link - Contents Mailing Lists - RSS Facebook - Tweet - linkedIn Cited by Published in ESR Vol. 39. Online publication date: July 11, 2019 Print ISSN: 1863-5407; Online ISSN: 1613-4796 Copyright © 2019 Inter-Research.

Population dynamics of the endangered Kemp’s ridley sea turtle following the 2010 oil spill in the Gulf of Mexico: Simulation of potential cause-effect relationships

The Kemp’s ridley (Lepidochelys kempii) is a critically endangered sea turtle that breeds nearly exclusively in the Gulf of Mexico, with scattered nesting along the U.S. Atlantic coast. In 2010, an unprecedented increase in strandings concomitant with a large oil spill in the northern Gulf raised concern about impacts on population recovery. We used several versions of an age-structured model representing hypothesized “pulse,” “press,” and “density-dependent remigration” effects of the 2010 mortality event to simulate post-2010 population dynamics. Only a “density-dependent remigration” version simulated population fluctuations observed from 2009 to 2014. Population dynamics projected through 2035 using this version indicated essentially exponential growth, with the simulated adult female population reaching ≈110,000 in 2035 (as indicated by nest counts at the index beach). Of most interest within a management context is the apparent resiliency of the population to large mortality events of short duration. Two important caveats to this statement are the assumptions that there has been no reduction of suitable habitats and that per capita availability of food resources is sufficient to support population recovery. Simulation results also provide insight into the myriad of potential responses of an age-structured population of long-lived animals to such events.

Drone Monitoring of Breeding Waterbird Populations: The Case of the Glossy Ibis

Waterbird communities are potential indicators of ecological changes in threatened wetland ecosystems and consequently, a potential object of ecological monitoring programs. Waterbirds often breed in largely inaccessible colonies in flooded habitats, so unmanned aerial vehicle (UAV) surveys provide a robust method for estimating their breeding population size. Counts of breeding pairs might be carried out by manual and automated detection routines. In this study we surveyed the main breeding colony of Glossy ibis (Plegadis falcinellus) at the Doñana National Park. We obtained a high resolution image, in which the number and location of nests were determined manually through visual interpretation by an expert. We also suggest a standardized methodology for nest counts that would be repeatable across time for long-term monitoring censuses, through a supervised classification based primarily on the spectral properties of the image and a subsequent automatic size and form based count. Although manual and automatic count were largely similar in the total number of nests, accuracy between both methodologies was only 46.37%, with higher variability in shallow areas free of emergent vegetation than in areas dominated by tall macrophytes. We discuss the potential challenges for automatic counts in highly complex images.

Population estimates of Bornean orang-utans using Bayesian analysis at the greater Batang Ai-Lanjak-Entimau landscape in Sarawak, Malaysia

The integration of Bayesian analysis into existing great ape survey methods could be used to generate precise and reliable population estimates of Bornean orang-utans. We used the Marked Nest Count (MNC) method to count new orang-utan nests at seven previously undocumented study sites in Sarawak, Malaysia. Our survey teams marked new nests on the first survey and revisited the plots on two more occasions; after about 21 and 42 days respectively. We used the N-mixture models to integrate suitability, abundance and detection models which account for zero inflation and imperfect detection for the analysis. The result was a combined estimate of 355 orang-utans with the 95% highest density interval (HDI) of 135 to 602 individuals. We visually inspected the posterior distributions of our parameters and compared precisions between study sites. We subsequently assess the strength or reliability of the generated estimates using identifiability tests. Only three out of the seven estimates had <35% overlap to indicate strong reliability. We discussed the limitations and advantages of our study design, and made recommendations to improve the sampling scheme. Over the course of this research, two of the study sites were gazetted as extensions to the Lanjak-Entimau Wildlife Sanctuary for orang-utan conservation.

Breeding eider ducks strongly influence subarctic coastal pond chemistry

Arctic freshwater ponds are typically pristine and oligotrophic, however seabird biovectors can markedly alter water quality via enrichment with marine-derived nutrients and bioaccumulated metals. These ornithogenic inputs can be the dominant factor structuring aquatic biota and the surrounding island flora. Here, we measured a suite of limnological water chemistry variables and sediment geochemistry from 21 freshwater ponds influenced by Common Eiders (Somateria mollissima) in Hudson Strait, near the northern communities of Cape Dorset (Nunavut) and Ivujivik (Quebec). Nest counts and sedimentary δ15N values were used as proxies of bird abundance. Nutrient-rich guano from the nesting eiders visibly promoted the growth of catchment vegetation. Elevated metal (Al, Cd, Zn), metalloid (Se), and nutrient concentrations (N, P) in the water of eider-affected sites were recorded (Sign test; p = 0.004), but the proximity of many sites to the coast meant that variables related to ocean spray (conductivity, Na+, Mg2+, Cl−, Sr) confounded the effects of birds on pond water chemistry. In contrast, sediment geochemistry appeared to more clearly characterize sites according to the level of eider activity in their catchments by tracking Pb, Cd, N, and P sedimentary concentrations (Sign test; p = 0.02). These results have direct implications for reconstructing historical eider population trends using sediment archives, which is necessary to inform effective conservation management strategies.

Utilization of Ficus benjamina by Birds at Urban Habitat in Depok

Most of the research about the relationship of birds and figs were conducted at natural habitat. We conducted a research about this relationship at urban habitat in Depok and specifically studied utilization of Ficus benjamina by birds as feeding and nesting tree. The objective of our research was to describe the F. benjamina utilization by urban birds in Depok. Scans sampling and nest counting were used during this study. Our research shows that F. benjamina was used as feeding tree by most of birds which lives at urban habitat in Depok. Our research also shows that some birds used this fig species as nesting tree. Key Words : birds, Ficus benjamina, urban, Java

Did Declining Carrying Capacity for the Kemp's Ridley Sea Turtle Population Within the Gulf of Mexico Contribute to the Nesting Setback in 2010−2017?

Abstract The Kemp's ridley (Lepidochelys kempii) is the most endangered sea turtle species. During 1966–2017, an annual count of nests (i.e., clutches of eggs laid) has served as an annual index of Kemp's ridley nesting female abundance on the Gulf of Mexico (GoM) index beach in Tamaulipas, Mexico. This index was increasing exponentially at 19% per year in 2009, but it dropped unexpectedly by more than a third in 2010 and through 2017 remained well below levels predicted. We hypothesize that pre-2010 declining carrying capacity for the Kemp's ridley population within the GoM contributed to this nesting setback. We discuss pre-2010 factors that may have caused carrying capacity to decline, including degradation of the GoM ecosystem, the exponentially increasing Kemp's ridley population, and declining per capita availability of neritic (i.e., postpelagic) Kemp's ridley food, including natural prey and scavenged discarded bycatch from shrimp trawling. We encourage evaluations (especially those within a robus...

Habitat utilisation and nesting behaviour of two sympatric weavers in Mbalmayo District, Cameroon

Avian ecology and behaviour data provides crucial information for bird conservation and management, but are still missing for many species, particularly in developing countries. This study examines habitat utilisation, nesting behaviour, anthropogenic disturbances and impacts on agricultural crops of Village Weaver Ploceus cucullatus and Vieillot’s Black Weaver Ploceus nigerrimus in Mbalmayo District, Cameroon. Abundance was estimated by nest counts and point counts of birds at 40 previously located colonies, where also tree metrics and anthropogenic disturbances were measured. In total, more than 1 700 birds of the two species were estimated within a 9 km2 study area, divided into two blocks and five different habitat types. Village Weavers were generally more abundant, especially in the urban habitat, whereas Vieillot’s Black Weavers were most numerous in the rural habitat. Among the tree species used for nesting, mango Mangifera indica and African border tree Newbouldia laevis had the highest nest counts, which also was positively related to canopy cover diameter. Traffic noise disturbance was associated with lower bird and nest counts, whereas the opposite was observed on farming disturbance. The relative impacts on agricultural crops were estimated for African oil palm Elaeis guineensis (38%), maize Zea mays (36%), Musa spp. (18%) and Mangifera indica (8%). The implications for long-term coexistence between farmland birds and humans are discussed, and the challenge is to minimise both kinds of bird–human interactions, i.e. anthropogenic disturbances and agricultural crop damage.

ГНІЗДУВАННЯ МАРТИНА ЖОВТОНОГОГО БІЛЯ КРЕМЕНЧУЦЬОЇ ГЕС

Introduction. Caspian Gull ( Larus cachinnans ) has started the expansion upstream the Dnieper after creation of the tandem reservoir system. This species began breeding at Kremenchuk reservoir in 1987. From 1990s new colonies were founded and number of the species increased. This tendency now continues. There were 1940-1990 pairs of this gull breeding in 6 colonies at Kremenchuk reservoir in 2015 according to our estimation. Purpose. Reevaluation of Caspian Gull ’s number at Kremenchuk reservoir. Methods. Inspection of territories suitable for breeding of Caspian Gull . Total count of nests in a colony. Results. New colony of the Caspian Gull was founded in 2017 near the Kremenchuk Hydroelectric power station . It situated at a concrete dam near the station. The dam has length 2 . 06 km and no plants. The colony is situated near the end of the dam and extending to 0.8 km. There were 750 pairs of Caspian Gulls breeding there in 2018. Gulls started breeding at this place at the beginning of 2000s. This breeding place is similar to colonies near the Kaniv and the Kyiv Hydroelectric power stations . The colony was founded due to expansion of the Caspian Gull on the Dnieper. We observed 5 birds with rings from another colonies at the Kremenchuk reservoir. Conclusion. Our new data allow overestimate the number of Caspian Gull at Kremenchuk reservoir approximately in 3000 pairs. It is the biggest population of this gull on the Dnieper river.

Seabird species vary in behavioural response to drone census

Unmanned aerial vehicles (UAVs) provide an opportunity to rapidly census wildlife in remote areas while removing some of the hazards. However, wildlife may respond negatively to the UAVs, thereby skewing counts. We surveyed four species of Arctic cliff-nesting seabirds (glaucous gull Larus hyperboreus, Iceland gull Larus glaucoides, common murre Uria aalge and thick-billed murre Uria lomvia) using a UAV and compared censusing techniques to ground photography. An average of 8.5% of murres flew off in response to the UAV, but >99% of those birds were non-breeders. We were unable to detect any impact of the UAV on breeding success of murres, except at a site where aerial predators were abundant and several birds lost their eggs to predators following UAV flights. Furthermore, we found little evidence for habituation by murres to the UAV. Most gulls flew off in response to the UAV, but returned to the nest within five minutes. Counts of gull nests and adults were similar between UAV and ground photography, however the UAV detected up to 52.4% more chicks because chicks were camouflaged and invisible to ground observers. UAVs provide a less hazardous and potentially more accurate method for surveying wildlife. We provide some simple recommendations for their use.

Development of a Survey Protocol for Monitoring Reddish Egrets (Egretta rufescens) in Florida, USA

Abstract The Reddish Egret (Egretta rufescens) is North America's rarest heron, and roughly 10% of its population resides in Florida. Its dark plumage, subcanopy nesting, and rarity make it difficult to count with aerial surveys, and assessments of ground- and boat-based methods for estimating the abundance of nesting pairs at breeding sites in Florida are lacking. The efficacy of flight-line surveys (boat-based counts of adults flying to and from colonies) and direct counts (ground- or boat-based counts of nests) were compared using data collected by multiple observers during repeated visits to 16 Reddish Egret colonies in three core breeding areas in the State of Florida, USA. Detection rates on direct counts were 77% for a single observer and 89% for two observers combined. Variance between repeated flight-line surveys was high (61%) for 1-hr surveys but substantially lower for 2-hr (18%) and 3-hr (14%) surveys. Estimated nest counts from flight-line surveys were substantially greater than those produc...

African apes coexisting with logging: Comparing chimpanzee (Pan troglodytes troglodytes) and gorilla (Gorilla gorilla gorilla) resource needs and responses to forestry activities

The extraction of timber often conflicts with the well-being and conservation of wildlife. In particular, there is a need to better understand the impact of tree removal under selective logging regimes on local ecological communities. We conducted ape nest counts along line transects before, during, and after logging to assess the impact of timber harvesting and associated activities on sympatric chimpanzees and gorillas in a forestry concession in northern Republic of Congo. We used generalized linear models to relate ape nest counts to a set of predictor variables, representing the impact of logging and controlled for variation in environmental conditions including food availability, habitat and rainfall. Commercial forest inventory data were used to assess the baseline influence of food availability and forest structure on ape distribution. Higher numbers of chimpanzees were found in proximity to their preferred tree foods, whereas gorillas were associated with more heterogeneous habitats. Chimpanzee nest encounter rates decreased with increasing intensity of human impacts. Gorillas also avoided areas with active timber exploitation and roads, but were attracted to recently logged areas with abundant terrestrial herbaceous vegetation. Species-specific responses were consistent with theoretical predictions of niche partitioning and cumulative human influence. Based on these findings, we provide recommendations to improve existing guidelines and forest certification standards aimed at safeguarding ape populations.

The albatross of assessing and managing risk for long-lived pelagic seabirds

Pelagic predators such as albatross have long been of conservation concern, but assessing their status poses numerous challenges. A standard monitoring method for albatross is colony-based nest counts to track numbers of breeders. However, a variable proportion of the population skips breeding in any given year and cannot be quantified by nest counts, creating several complications to efforts in understanding population dynamics. We used stochastic demographic matrix models for black-footed (Phoebastria nigripes) and Laysan (P. immutabilis) albatross to investigate: i) the potential for the skipping behavior of breeders to create apparent density dependence in nest counts, ii) the limitations to assessing population trends from nest counts and implications for evaluating impacts from fisheries bycatch, including calculating Potential Biological Removal values, and iii) the relative importance of at-sea versus on-island threats to population viability. We found the increased likelihood of these albatrosses skipping breeding following a successful season – a feature common to many seabirds and other taxa – results in substantial negative temporal auto-correlation in the observable population that can be misinterpreted as negative density dependence, with important implications for inferences about population viability. Black-footed albatross appear limited by fisheries bycatch, while Laysan albatross, which have low estimated bycatch mortality, are currently at greater risk from island-based threats. Our results suggest a cautionary approach to managing black-footed and Laysan albatross should be adopted because detecting population declines from nest counts could take decades. Ultimately, we highlight the inherent difficulties in assessing population status and trends in long-lived species such as albatross.