Estimating the population size of a threatened arboreal marsupial: use of distance sampling to dispense with ad hoc survey techniques

2010 ◽  
Vol 37 (6) ◽  
pp. 512 ◽  
Author(s):  
Paul J. de Tores ◽  
Sue Elscot
Keyword(s):  
Land Use ◽  
Population Size ◽  
Ad Hoc ◽  
Conservation Status ◽  
Distance Sampling ◽  
Potential Effect ◽  
Decision Makers ◽  
Biological Information ◽  
Line Transect ◽  
Land Use Decisions

Context. Long-term land-use decisions potentially affecting the conservation status of rare fauna are often based on a dearth of relevant biological information and population estimates are regularly derived from ad hoc methodologies. This can significantly affect the outcomes from development assessment and approval processes. Aim. Our aims were to apply distance-sampling techniques to derive robust, quantitative estimates of the population size of a threatened arboreal marsupial, the western ringtail possum (Pseudocheirus occidentalis Thomas, 1888), demonstrate the advantages of this approach and, in doing so, provide conservation managers, decision makers and consultants with a reliable framework for surveying the species. Methods. We used line-transect sampling to derive estimates of density and abundance for P. occidentalis at two sites in south-western Western Australia where estimates were previously derived through ad hoc techniques. Key results. Our findings support the assertion that previous surveys of P. occidentalis populations have underestimated the population size to a varying extent at both of our survey sites. Land-use and development-application decisions have previously been based on similar surveys. Conclusions. Distance sampling, if applied routinely when surveying P. occidentalis, will reduce the uncertainty associated with derived estimates of abundance. Implications. Appropriate use of distance-sampling methods will enable managers and decision makers to assess more quantitatively the potential effect from, and place appropriate approval conditions on, proposals that modify or destroy P. occidentalis habitat. The use of the program Distance will enable such decisions to be based on robust, repeatable estimates of population size, with quantified confidence limits and variance estimates.

scholarly journals Spatial distribution of the Barbary Partridge (Alectoris barbara) in Sardinia explained by land use and climate

2021 ◽  
Vol 67 (4) ◽  
Author(s):  
Gianpasquale Chiatante ◽  
Marta Giordano ◽  
Anna Vidus Rosin ◽  
Oreste Sacchi ◽  
Alberto Meriggi
Keyword(s):  
Land Use ◽  
Conservation Status ◽  
Distance Sampling ◽  
Strong Relationship ◽  
European Population ◽  
Factors Affecting ◽  
Brood Rearing ◽  
Management Actions ◽  
Negative Effect ◽  
Study Sites

AbstractMore than half of the European population of the Barbary Partridge is in Sardinia; nonetheless, the researches concerning this species are very scarce, and its conservation status is not defined because of a deficiency of data. This research aimed to analyse the habitat selection and the factors affecting the abundance and the density of the Barbary Partridge in Sardinia. We used the data collected over 8 years (between 2004 and 2013) by spring call counts in 67 study sites spread on the whole island. We used GLMM to define the relationships between the environment (topography, land use, climate) both the occurrence and the abundance of the species. Moreover, we estimated population densities by distance sampling. The Barbary Partridge occurred in areas at low altitude with garrigue and pastures, avoiding woodlands and sparsely vegetated areas. We found a strong relationship between the occurrence probability and the climate, in particular, a positive relation with temperature and a negative effect of precipitation, especially in April–May, during brood rearing. Furthermore, dry crops positively affected the abundance of the species. We estimated a density of 14.1 partridges per km2, similar to other known estimates. Our findings are important both because they increase the knowledge concerning this species, which is considered data deficient in Italy, and because they are useful to plan management actions aimed to maintain viable populations if necessary.

The importance of survey design in distance sampling: field evaluation using domestic sheep

2011 ◽  
Vol 38 (3) ◽  
pp. 221 ◽  
Author(s):  
Tom A. Porteus ◽  
Suzanne M. Richardson ◽  
Jonathan C. Reynolds
Keyword(s):  
Population Size ◽  
Survey Design ◽  
Distance Sampling ◽  
Field Evaluation ◽  
Stage I ◽  
Stage Ii ◽  
Line Transect ◽  
Domestic Sheep ◽  
Management Decisions ◽  
Mobile Species

Context Sampling methods to estimate animal density require good survey design to ensure assumptions are met and sampling is representative of the survey area. Management decisions are often made based on these estimates. However, without knowledge of true population size it is not possible for wildlife biologists to evaluate how biased the estimates can be if survey design is compromised. Aims Our aims were to use distance sampling to estimate population size for domestic sheep free-ranging within large enclosed areas of hill country and, by comparing estimates against actual numbers, examine how bias and precision are impaired when survey design is compromised. Methods We used both line and point transect sampling to derive estimates of density for sheep on four farms in upland England. In Stage I we used limited effort and different transect types to compromise survey design. In Stage II we increased effort in an attempt to improve on the Stage I estimates. We also examined the influence of a walking observer on sheep behaviour to assess compliance with distance sampling assumptions and to improve the fit of models to the data. Key results Our results show that distance sampling can lead to biased and imprecise density estimates if survey design is poor, particularly when sampling high density and mobile species that respond to observer presence. In Stage I, walked line transects were least biased; point transects were most biased. Increased effort in Stage II reduced the bias in walked line transect estimates. For all estimates, the actual density was within the derived 95% confidence intervals, but some of these spanned a range of over 100 sheep per km2. Conclusions Using a population of known size, we showed that survey design is vitally important in achieving unbiased and precise density estimation using distance sampling. Adequate transect replication reduced the bias considerably within a compromised survey design. Implications Management decisions based on poorly designed surveys must be made with an appropriate understanding of estimate uncertainty. Failure to do this may lead to ineffective management.

scholarly journals Current status and conservation of the Endangered Przewalski's gazelle Procapra przewalskii, endemic to the Qinghai–Tibetan Plateau, China

Oryx ◽  
2012 ◽  
Vol 46 (1) ◽  
pp. 145-153 ◽  
Author(s):  
Chunlin Li ◽  
Zhigang Jiang ◽  
Xiaoge Ping ◽  
Jing Cai ◽  
Zhangqiang You ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Population Size ◽  
Conservation Status ◽  
Distance Sampling ◽  
Current Status ◽  
Qinghai Lake ◽  
Conservation Strategies ◽  
Lake Basin ◽  
Domestic Livestock ◽  
Procapra Przewalskii

AbstractIn 2008 Przewalski's gazelle Procapra przewalskii, endemic to the Qinghai–Tibetan Plateau, China, was recategorized from Critically Endangered to Endangered on the IUCN Red List. The species is still, however, threatened, and the human population and accompanying domestic livestock are increasing around Qinghai Lake. Here we provide up-to-date information on the distribution and population size of the species, evaluate its current conservation status and discuss the difficulties of protecting this gazelle species. We used both distance sampling and total counts to survey 16 sites where the species has been reported and found it at 13 of these, occupying a total area of c. 250 km2. Population size estimated from distance sampling (1,635) and total counts (1,544) was similar. About 20% of the gazelles located were in newly discovered areas for the species. The results indicate an overall growth in the population of Przewalski's gazelle since 2003, although some subpopulations have declined or been extirpated. In spite of conservation efforts Przewalski's gazelle is still threatened by habitat degradation and loss, habitat fragmentation, fencing, intensified competition with domestic livestock and predation. Further growth of this gazelle population is constrained by limited habitat availability and human–gazelle conflict. We recommend that management and conservation strategies need to incorporate comprehensive knowledge of the gazelle, long-term monitoring, and captive breeding of injured and orphaned gazelles to form a potential pool of individuals for future reintroductions to the historical range of the species outside the Qinghai Lake basin.

Precision, accuracy and bias of walked line-transect distance sampling to estimate eastern grey kangaroo population size

2015 ◽  
Vol 42 (8) ◽  
pp. 633 ◽  
Author(s):  
Ruth Glass ◽  
David M. Forsyth ◽  
Graeme Coulson ◽  
Marco Festa-Bianchet
Keyword(s):  
Population Size ◽  
Distance Sampling ◽  
Accurate Method ◽  
Line Transect ◽  
Good Precision ◽  
Design Elements ◽  
Abundance Estimates ◽  
Grey Kangaroo ◽  
Eastern Australia ◽  
Free Ranging

Context Distance sampling is widely used to estimate the size of wildlife populations, including kangaroos. However, the performance of distance-sampling abundance estimates has seldom been evaluated for wild mammal populations of known size. Aims We evaluated the precision, accuracy, bias and interval coverage of abundance estimates from walked line-transect sampling, a commonly used distance-sampling method, for a marked free-ranging population of eastern grey kangaroos (Macropus giganteus) at Yanakie Isthmus, Wilsons Promontory National Park, south-eastern Australia. Methods In each of two study periods (November 2012 and May 2013) we first determined the true size of the uniquely marked kangaroo population by conducting 10 intensive searches of the study area. We then conducted distance sampling along six systematically spaced line transects. We walked each transect four times in November 2012 and seven times in May 2013. Data were analysed using Program DISTANCE. Key results Our intensive searches revealed that 141 and 124 collared kangaroos were present in the study area in November 2012 and May 2013, respectively. When transects were walked four or more times (i.e. ≥400 observations), maximum precision (coefficient of variation; CV of ~13%) was achieved in both survey periods. Walking transects twice (i.e. ~200 observations) produced abundance estimates with CVs of <20% in each study period. The accuracy (root mean square error) of abundance estimates varied from 1 to 13 (November 2012) and from 3 to 28 (May 2013). Bias ranged from −9% to +23%, but stabilised at between −1% and −9% when transects were walked four or more times in each study period. The 95% confidence intervals for the abundance estimates always included the true population size. Conclusions Our results indicated that walked line-transect distance sampling is a precise and accurate method for estimating eastern grey kangaroo abundance. The small negative biases that occurred when sample sizes were large were likely to be due to some animals moving outside the study area. Implications Provided that the key design elements and assumptions are met, estimates of kangaroo abundance from walked line-transect distance sampling should have good precision (CV < 20%) and minimal (<10%) bias.

scholarly journals Out of the darkness: the first comprehensive survey of the Critically Endangered Anjouan Scops Owl Otus capnodes

2014 ◽  
Vol 25 (3) ◽  
pp. 322-334 ◽  
Author(s):  
KATHLEEN E. GREEN ◽  
BRONWEN M. DANIEL ◽  
SAMUEL P. LLOYD ◽  
ISHAKA SAID ◽  
AMELAID HOUMADI ◽  
...  
Keyword(s):  
Population Size ◽  
Conservation Status ◽  
Distance Sampling ◽  
Bird Species ◽  
Iucn Red List ◽  
Critically Endangered ◽  
Encounter Rate ◽  
Wet Season ◽  
Point Counts ◽  
Comprehensive Survey

SummaryAlthough birds are among the best studied taxa, many of the globally threatened species lack the information required to fully assess their conservation status and needs. One such species is the Anjouan Scops Owl Otus capnodes which was presumed extinct until its rediscovery to science in 1992. Based on the limited extent and decline of the moist forests in the highlands of Anjouan in the Comoro Islands, a population size of only 100–200 pairs was estimated and the species was classified as ‘Critically Endangered’. The current study is the first comprehensive survey ever conducted on this species, and aimed to establish the current distribution and population size. Point counts with distance sampling were conducted across the agroforestry and forest zones of Anjouan in both a dry and wet season. A niche suitability model predicted the species distribution to be wider than expected with owls observed as low as 300 m altitude and in highly modified agroforestry habitats. However, the encounter rate in natural relatively undisturbed forest was significantly greater than in other habitats. The wider than expected geographic range of O. capnodes supports a possible downlisting of this species on the IUCN Red List to ‘Endangered’. Population size was found to be far greater than previously thought, at approximately 3,450 individual owls in the dry season and 5,450 in the wet season. These results show the importance of investing in robust surveys of poorly known and cryptic bird species, and provide up to date and important information for landscape scale conservation planning in the Comoros Islands.

scholarly journals Aerial line transect survey to estimate abundance of marsh deer (Blastocerus dichotomus) (Illiger, 1815)

2005 ◽  
Vol 48 (5) ◽  
pp. 807-814 ◽  
Author(s):  
Artur Andriolo ◽  
Ubiratan Piovezan ◽  
Mateus José Rodrigues Paranhos da Costa ◽  
Jeff Laake ◽  
José Maurício Barbanti Duarte
Keyword(s):  
Population Size ◽  
River Basin ◽  
Distance Sampling ◽  
Aerial Survey ◽  
Line Transect ◽  
Sampling Methodology ◽  
Future Analysis ◽  
Line Transect Survey ◽  
Blastocerus Dichotomus ◽  
The Impact

The objective was to estimate abundance of marsh deer in the Paraná River basin of this work. The results provided information to support further analysis of the impact of the Porto Primavera flooding lake over population. Sixty-nine animals were recorded by aerial survey using distance sampling methodology. Animals were widely distributed throughout the study area. The uncorrected data resulted in a estimate density of 0.0035 ind/ha and a population size of 636 individuals. Correcting the g for the animals that could be missed the calculated abundance was 896 (CV=0.27) individuals. This methodology was applied with success to survey marsh deer. The result was important to evaluate the marsh deer status in the area, and for future analysis of the impact of the flooding dam.

scholarly journals Tendencias poblacionales recientes de la avutarda hubara en las Islas Canarias: análisis metodológico y estado de conservación

2012 ◽  
Vol 35 (1) ◽  
pp. 125-139
Author(s):  
C. Schuster ◽  
◽  
J. J. Iglesias-Lebrija ◽  
L. M. Carrascal ◽  
◽  
...  
Keyword(s):  
Canary Islands ◽  
Conservation Status ◽  
Distance Sampling ◽  
Small Variation ◽  
Population Trends ◽  
Line Transect ◽  
Sampling Area ◽  
Average Value ◽  
Houbara Bustard ◽  
Population Sizes

Recent population trends of the houbara bustard in the Canary Islands. Methods and conservation status Determining conservation status requires rigorous and reliable data about population sizes and trends, especially if they have to be applied to islands where the species have small populations. The Canary bustard houbara (Chlamydotis undulata fuertaventurae) is catalogued as ‘in danger’ by the Red Book of the Birds of Spain. This work analyzes the value of previously published information on the species using the method of adjacent linear transects separated by 200 m, as a baseline for establishing robust population trends in 30 important areas (ranging from 1.3 to 12.8 km2) for the houbara in the islands of Lanzarote and Fuerteventura (Canary Islands). Censuses were repeated on the same dates (from November to December) and localities as those carried out in 1994, 2004 and 2006. The detection probability of the houbara was estimated by means of distance sampling, being 0.42 up to 250 m from the observer, and 0.82 in the main census belt of 100 m on either side of the line transect. The method of adjacent linear transects —counting the maximum number of hubaras detected— provides accurate figures of population densities (detection of 95.2% of the birds). The previous estimations of houbara densities can therefore be considered highly trustworthy, with a probable average underestimation of only 5 %. Nevertheless, the confidence intervals of density estimations using only one census were very large. Therefore, with only one census per sampling area and year it is not possible to obtain precise estimates of houbara densities with small variation around the average value. This raises concern when trying to obtain solid evidence about the increases–decreases of houbara populations comparing different dates or study areas. The density of the Canary Island hubara bustard decreased significantly from 2004/2006 to 2011 in eight areas of Fuerteventura (Vega Vieja, Los Alares–Pocetas, Matas Blancas, Lorenzo– Diviso, Corralejo, Lajares and Fimapaire) and in two areas of Lanzarote (Argana and La Santa). Conversely, the density of the houbara significantly increased in three areas of Lanzarote (Zonzamas, Guatiza and Llano de las Maretas). As a whole, average population density did not differ significantly between 2004/2006 and 2011 in Fuerteventura (slight decrease of 29% in 2011), but there was a significant increase in Lanzarote (increase of 60% from 2004/2006 to 2011). The change in density from 2004/2006 to 2011 tended to be an increase in areas further from paved roads, and a decrease in locations predominantly covered by loose sandy soils.

scholarly journals Population size and human-grivet monkeys (Chlorocebus aethiops) conflict in Zegie peninsula, Bahir Dar, Ethiopia

BMC Zoology ◽  
2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Yibelu Yitayih ◽  
Dessalegn Ejigu ◽  
Misganaw Mola
Keyword(s):  
Population Size ◽  
Conservation Status ◽  
Population Estimate ◽  
Line Transect ◽  
Human Food ◽  
Chlorocebus Aethiops ◽  
Significant Difference ◽  
Dry Seasons ◽  
The Impact ◽  
Wet And Dry Seasons

Abstract Background Human-monkey conflict exists in different forms all over the world and is experienced more in developing countries. The conflict between human and grivet monkey (Chlorocebus aethiops) ranks among the main threats to biodiversity conservation and has become frequent and severe in different parts of Africa. A study on population size and human-grivet monkey conflict in Zegie Peninsula was carried out from August 2019 to March 2020; the study comprised both the wet and dry seasons. The line transect method was used to collect data on the population size of grivet monkeys. Questionnaires and focus group discussions were used to study the human-grivet monkey conflict and its conservation status. Results The estimated population of grivets in the study area was 5046. Population structure of grivets indicated that there were 637 adult males, 1246 adult females, 1839 juveniles, and 1324 infants. The number of grivets in different habitat was; 1925 grivets in agricultural area, 1568 in lakeshore, 988 in forest and 565 grivets in shrub. Grivet population estimate between the wet and dry seasons did not show significant differences (χ2 = 0.941, df = 1, p > 0.05). But there was a significant difference in the population estimate of grivets among the different habitats (χ2 = 239.135, df = 3, p < 0.05 and among their age/sex (χ2 = 504.102, df = 3, p < 0.05. Based on the questionnaire result the most problematic crop pests in the area were grivet monkeys (96.4%), bush pigs (52.3%), porcupine (46.3%) and squirrels cover (33.2%). The result of discussions held with focus groups and questionnaires in the study area showed that grivet monkeys damage crops (98.4%), chicken depredation (49.5%), steal and snatch human food (32%), disturbing communities (11.3%) in the area. Most (62%) of the respondents noted that guava is the most vulnerable crop followed by papaya, mango, avocado to be damaged by grivet monkeys. Conclusion The total number of grivet monkey in the study area is 5046. The number of grivet monkeys varies based on their sex/age and their habitat type. There is no significant difference in their number according to season since the movement of grivets is restricted to the area (there is no migration in the area). The increasing population number leads the occurrence of human grivet monkey conflict in the area and this inversely affects grivet monkeys. There was a human-grivet monkey conflict in the Peninsula and grivets damaged crops, not only crops but also predating poultry, stealing eggs, and human food. Consequently, grivets were killed in response to the damage they caused to crops. Grivet’s habitat in the Peninsula is highly disturbed because the local people cut trees for sale to support their livelihood. Awareness creation of the residents about wildlife and their habitat is necessary, and people should understand the impact of deforestation, illegal hunting, and the role of grivets in the ecosystem at large. Hence there is a need to protect the forest in order to ensure sustainable conservation of biodiversity in general and grivet monkeys in particular.

State of Conservation and Population Structure of Bird Species Inhabiting in Various Subtropical Urban Forests

2021 ◽  
Author(s):  
M. N. Rajpar ◽  
M. Zakaria
Keyword(s):  
Population Structure ◽  
Conservation Status ◽  
Distance Sampling ◽  
Bird Species ◽  
Urban Forests ◽  
Avian Species ◽  
Bird Diversity ◽  
Line Transect ◽  
Distance Analysis ◽  
Wide Range

Abstract To determine the conservation status and population structure of avian species living in various subtropical broadleaved urban forests, namely Dob Ghar, Kamal Khan, Kityari, Palamar, Seya Sar and Shahabad of Pakistan, we aimed to use the distance sampling line transect process. To avoid double counting of the same bird individual, a total of 180 counting points were set at 250 m from each other. In all, between December 2017 and November 2018, 2,879 individuals representing 53 species, 28 families and 9 orders were detected. One species was vulnerable (VU) out of 53 bird species, while the remaining 52 species were the least concerned (LC). In particular, the results of the distance analysis indicate that, in six subtropical broad-leaved forests, the bird population can vary. For eg, Palamar (0.954 ± 0.221 birds/ha) and Kityari (0.938 ± 0.162 birds/ha) were densely populated by bird species, while Kamal Khan (0.102 ± 0.178 birds/ha) was less concerm. Similarly, the CAP findings showed that bird species in Dob Ghar were more diverse (H’ = 33.92 ± 1.368) and equally distributed (E = 0.9657 ± 0.004) and that the Shahabad ecosystem was rich in bird species (R1 = 8.007 ± 0.053) compared to other habitats. In addition, the length of the twigs and topological changes in the dendrogram have shown that bird diversity may vary from habitat to habitat. The bird species were classified into eight foraging guilds. Insectivores were the most abundant bird species using all habitats in abundance. By cons, Carnivore/Piscivore/Insectivore averted to use the forest habitats Dob Ghar and Frugivore Kamal Khan and Dob Ghar. The findings of this study revealed that broad-leaved subtropical urban forests are home to a wide range of avian species. However, habitat selection among bird species varied across habitats according to vegetation structure and composition, food resources, adjoining habitats, and human settlements.

scholarly journals Status assessment of the Critically Endangered Azores Bullfinch Pyrrhula murina

2011 ◽  
Vol 21 (4) ◽  
pp. 477-489 ◽  
Author(s):  
RICARDO S. CEIA ◽  
JAIME A. RAMOS ◽  
RUBEN H. HELENO ◽  
GEOFF M. HILTON ◽  
TIAGO A. MARQUES
Keyword(s):  
Population Size ◽  
Conservation Status ◽  
Distance Sampling ◽  
Iucn Red List ◽  
Range Size ◽  
Critically Endangered ◽  
Survey Method ◽  
Mountain Range ◽  
Laurel Forest ◽  
Area Of Occupancy

SummaryThe Azores Bullfinch is endemic to the island of São Miguel (Azores, Portugal). Its status was uplisted to Critically Endangered in 2005 on the basis of an extremely small and declining population that was considered to be restricted to a very small mountain range (43 km2), in a single location, within which the spread of invasive plants constituted a threat to habitat quality. Nevertheless, information was mostly inferred, or the product of, non-systematic studies. In order to carry out a complete assessment of the conservation status we analysed: (i) population trend, calculated from annual monitoring 1991–2008, (ii) population size, and (iii) range size, obtaining estimates in a single morning study in 2008 involving the simultaneous participation of 48 observers. Contrary to previous inferences, the population is no longer decreasing, although quality of laurel forest habitat continues to decline due to the persistent threat of invasive species. Population size (mean ± SE) was estimated at 1,064 ± 304 individuals using distance sampling methods, although the estimate was very sensitive to the survey method used. Range size estimates (extent of occurrence and area of occupancy) were 144 km2 and 83 km2 respectively. Given the present information, we propose the downlisting of Azores Bullfinch to Endangered on the IUCN Red List.

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