Aerial surveys of multiple species: critical assumptions and sources of bias in distance and mark - recapture estimators

2008 ◽  
Vol 35 (4) ◽  
pp. 310 ◽  
Author(s):  
Gavin J. Melville ◽  
John P. Tracey ◽  
Peter J. S. Fleming ◽  
Brian S. Lukins
Keyword(s):  
Line Transect ◽  
Implicit Assumption ◽  
Distance Method ◽  
Mark Recapture ◽  
Transect Line ◽  
Aerial Surveys ◽  
Transect Sampling ◽  
Multiple Covariates ◽  
Recent Developments ◽  
Multiple Species

Recent developments in the application of line-transect models to aerial surveys have used double-observer sampling to account for undercounting on the transect line, a crucial step in obtaining correct population estimates. This method is commonly called the mark–recapture line-transect sampling method and estimates the detection probability at zero distance to correct line-transect estimates of abundance. An alternative approach, which uses the same methodology during data collection, is to use a range of covariates, including distance from the transect, in a mark–recapture model. This approach overcomes the implicit assumption of uniform distribution of distances in line-transect estimators. In this paper, we use three alternative approaches (a multiple-covariates distance method, a distance method incorporating adjustment for incomplete detection on the transect line using mark–recapture sampling, and a mark–recapture method with distance as a covariate) to estimate the abundance of several medium-sized mammals in semiarid ecosystems. Densities determined with the three estimators varied considerably within species and sites. In some cases distance estimates were larger than mark–recapture estimates and vice versa. Despite large numbers of observations, distance uniformity was not observed for any species at any site, nor for any species where sites were combined. Possible reasons, which include sampling variability, movement in response to the aircraft and failure of the mark–recapture independence assumption, are discussed in detail.

Detectability of penguins in aerial surveys over the pack-ice off Antarctica

2008 ◽  
Vol 35 (4) ◽  
pp. 349 ◽  
Author(s):  
Colin Southwell ◽  
Charles G. M. Paxton ◽  
David L. Borchers
Keyword(s):  
Aerial Survey ◽  
Line Transect ◽  
Mark Recapture ◽  
Transect Line ◽  
Aerial Surveys ◽  
Abundance Estimates ◽  
Transect Sampling ◽  
Pack Ice ◽  
Additional Costs ◽  
Ice Floes

Knowledge of penguin abundance at regional and circumpolar scales across the Southern Ocean is important for the development of ecosystem models and to estimate prey consumption by penguins to assess potential competition with fisheries’ operations. One means of estimating penguin abundance is to undertake aerial surveys across the pack-ice surrounding Antarctica where penguins forage. However, it has long been recognised that aerial counts and resultant abundance estimates are likely to be negatively biased unless detectability is estimated and taken into account. Mark–recapture line-transect methods were used to estimate the detectability of penguin groups resting on ice floes during helicopter surveys over the pack-ice off Antarctica. Group size had the greatest effect of several measured covariates on detectability. Despite a concerted effort to meet the central assumption of conventional line-transect sampling (all objects on the transect line are detected), this was close to being achieved by single observers only in the case of the occasional very large group of >20 penguins. Emperor penguins were more detectable than Adélie penguins. Although observers undertook an extensive simulation training program before the survey, overall they improved in their ability to detect penguin groups throughout the survey. Mark–recapture line-transect methods can provide less biased estimation than conventional line-transect methods in aerial survey applications. This improvement comes with some costs, including the need for more demanding data-recording procedures and the need to use larger, more expensive aircraft. These additional costs will often be small compared with the basic cost, but the gain in terms of improved estimation may be substantial.

scholarly journals The influence of animal mobility on the assumption of uniform distances in aerial line-transect surveys

2008 ◽  
Vol 35 (4) ◽  
pp. 275 ◽  
Author(s):  
Rachel M. Fewster ◽  
Colin Southwell ◽  
David L. Borchers ◽  
Stephen T. Buckland ◽  
Anthony R. Pople
Keyword(s):  
Survey Design ◽  
Distance Sampling ◽  
High Mobility ◽  
Line Transect ◽  
Transect Line ◽  
Aerial Surveys ◽  
Pack Ice ◽  
Capture Recapture ◽  
Distance Data ◽  
Crabeater Seals

Line-transect distance sampling is a widely used method for estimating animal density from aerial surveys. Analysis of line-transect distance data usually relies on a requirement that the statistical distribution of distances of animal groups from the transect line is uniform. We show that this requirement is satisfied by the survey design if all other assumptions of distance sampling hold, but it can be violated by consistent survey problems such as responsive movement of the animals towards or away from the observer. We hypothesise that problems with the uniform requirement are unlikely to be encountered for immobile taxa, but might become substantial for species of high mobility. We test evidence for non-uniformity using double-observer distance data from two aerial surveys of five species with a spectrum of mobility capabilities and tendencies. No clear evidence against uniformity was found for crabeater seals or emperor penguins on the pack-ice in East Antarctica, while minor non-uniformity consistent with responsive movement up to 30 m was found for Adelie penguins. Strong evidence of either non-uniformity or a failure of the capture–recapture validating method was found for eastern grey kangaroos and red kangaroos in Queensland.

Line Transect Sampling Under Varying Conditions with Application to Aerial Surveys

Ecology ◽  
1996 ◽  
Vol 77 (4) ◽  
pp. 1297-1302 ◽  
Author(s):  
Pham X. Quang ◽  
Earl F. Becker
Keyword(s):  
Line Transect ◽  
Line Transect Sampling ◽  
Aerial Surveys ◽  
Transect Sampling

Visibility bias in aerial survey: mark - recapture, line-transect or both?

2008 ◽  
Vol 35 (4) ◽  
pp. 299 ◽  
Author(s):  
Jeff Laake ◽  
Michelle J. Dawson ◽  
Jim Hone
Keyword(s):  
Hybrid Approach ◽  
Aerial Survey ◽  
Line Transect ◽  
Line Transect Sampling ◽  
Detection Function ◽  
Mark Recapture ◽  
Hybrid Approaches ◽  
Transect Sampling ◽  
Eastern Australia ◽  
Sampling Procedures

Mark–recapture and line-transect sampling procedures both provide estimators for visibility bias in aerial surveys, and have coexisted in the literature for decades. Mark–recapture estimators of abundance tend to be negatively biased in this context as a result of unmodelled heterogeneity. Line-transect sampling can also be negatively biased if detection probability on the line is less than 1.0. Numerous papers have described hybrid approaches using mark–recapture and line transect methods but there have been some subtle but important differences that may not be apparent to the practitioner. We have used wild horse survey data collected in south-eastern Australia and some imaginary data to highlight these subtle differences. We demonstrate the advantage of using the hybrid approach, which uses the strengths of both mark–recapture and line-transect procedures by fitting a detection function (with p(0) = 1) to the line-transect data to estimate the shape of the detection function, and uses a separate detection function for the mark–recapture data to estimate the intercept (p(0)).

scholarly journals A comparison of mark - recapture distance-sampling methods applied to aerial surveys of eastern grey kangaroos

2008 ◽  
Vol 35 (4) ◽  
pp. 320 ◽  
Author(s):  
Rachel M. Fewster ◽  
Anthony R. Pople
Keyword(s):  
Goodness Of Fit ◽  
Distance Sampling ◽  
Density Estimates ◽  
Mark Recapture ◽  
Transect Line ◽  
Aerial Surveys ◽  
Commercial Harvest ◽  
Coefficients Of Variation ◽  
Detection Probabilities ◽  
Full Independence

Aerial surveys of kangaroos (Macropus spp.) in Queensland are used to make economically important judgements on the levels of viable commercial harvest. Previous analysis methods for aerial kangaroo surveys have used both mark–recapture methodologies and conventional distance-sampling analyses. Conventional distance sampling has the disadvantage that detection is assumed to be perfect on the transect line, while mark–recapture methods are notoriously sensitive to problems with unmodelled heterogeneity in capture probabilities. We introduce three methodologies for combining together mark–recapture and distance-sampling data, aimed at exploiting the strengths of both methodologies and overcoming the weaknesses. Of these methods, two are based on the assumption of full independence between observers in the mark–recapture component, and this appears to introduce more bias in density estimation than it resolves through allowing uncertain trackline detection. Both of these methods give lower density estimates than conventional distance sampling, indicating a clear failure of the independence assumption. The third method, termed point independence, appears to perform very well, giving credible density estimates and good properties in terms of goodness-of-fit and percentage coefficient of variation. Estimated densities of eastern grey kangaroos range from 21 to 36 individuals km–2, with estimated coefficients of variation between 11% and 14% and estimated trackline detection probabilities primarily between 0.7 and 0.9.

scholarly journals Estimating a resource selection function with line transect sampling

2002 ◽  
Vol 6 (4) ◽  
pp. 213-228 ◽  
Author(s):  
Bryan F. J. Manly
Keyword(s):  
Resource Selection ◽  
Probability Function ◽  
Resource Selection Function ◽  
Line Transect ◽  
Selection Function ◽  
Line Transect Sampling ◽  
Selection Probability ◽  
Transect Sampling ◽  
Conditional Maximum ◽  
Habitat Variables

A resource selection probability function is a function that gives the prob- ability that a resource unit (e.g., a plot of land) that is described by a set of habitat variables X1 to Xp will be used by an animal or group of animals in a certain period of time. The estimation of a resource selection function is usually based on the comparison of a sample of resource units used by an animal with a sample of the resource units that were available for use, with both samples being assumed to be effectively randomly selected from the relevant populations. In this paper the possibility of using a modified sampling scheme is examined, with the used units obtained by line transect sampling. A logistic regression type of model is proposed, with estimation by conditional maximum likelihood. A simulation study indicates that the proposed method should be useful in practice.

Population structure, density and biomass of large herbivores in the tropical forests of Nagarahole, India

1992 ◽  
Vol 8 (01) ◽  
pp. 21-35 ◽  
Author(s):  
K. Ullas Karanth ◽  
Melvin E. Sunquist
Keyword(s):  
Population Structure ◽  
Tropical Forests ◽  
Primate Species ◽  
Line Transect ◽  
Large Herbivore ◽  
Large Herbivores ◽  
Transect Sampling ◽  
Structure Density ◽  
Density And Biomass ◽  
Turn Over

ABSTRACTWe studied the population structure, density and biomass of seven ungulate and two primate species in the tropical forests of Nagarahole, southern India, using line transect sampling and roadside/platform counts, during 1986–87. The estimated ecological densities of large herbivore species in the study area are: 4.2 muntjac km−2, 50.6 chital km−2, 5.5 sambar km−2, 0.8 four-horned antelope km−2, 9.6 gaur km−2, 4.2 wild pig km−2, 3.3 elephant km−2, 23.8 hanuman langur km−2and 0.6 bonnet macaque km−2. Most ungulates have female-biased adult sex ratios. Among common ungulate species, yearlings and young of the year comprise about a third of the population, suggesting relatively high turn-over rates. Three species (muntjac, sambar and four-horned antelope) are solitary, while others form groups. The study area supports a wild herbivore biomass density of 14,744 kg km−2. Among the three habitat types within the study area, biomass is lower in dry deciduous forests when compared with moist deciduous or teak plantation dominant forests. Using our results, we have examined the factors that may contribute towards maintenance of high ungulate biomass in tropical forests.

scholarly journals KEPADATAN POPULASI MAMALIA DARAT KARNIVORA DI CAMP LEAKEY KAWASAN TAMAN NASIONAL TANJUNG PUTING, KALIMANTAN TENGAH

Jurnal BIOMA ◽  
2017 ◽  
Vol 12 (2) ◽  
pp. 83
Author(s):  
Siwi Arthapati Mandiri ◽  
Paskal Sukandar ◽  
Yossa Istiadi
Keyword(s):  
Data Collection ◽  
Population Density ◽  
National Park ◽  
Line Transect ◽  
Line Transect Sampling ◽  
Clouded Leopard ◽  
Helarctos Malayanus ◽  
Transect Sampling ◽  
Palm Civet ◽  
Leopard Cat

Borneo has wide land that support high biodiversity. One of them is Tanjung Puting National Park (TPNP), which have biodiversity such as terrestrial mammalian carnivore. Carnivore has a role to maintain its ecosystems. But, there are no data for population density of terrestrial mammalian carnivore. The object of this research is to find out population density of terrestrial mammalian carnivore in Camp Leakey, TPNP, Central Borneo. This research accomplished in September-October 2015 in Camp Leakey. Using line-transect sampling. Data collection was accomplished at 18.00-24.00 Central Indonesian Time (WITA) on eight transects with three times replication by direct surveys and indirect surveys. This research has obtained five species, malayan sun bear (Helarctos malayanus), sunda clouded leopard (Neofelis diardi), leopard cat, and group of civet, like small-toothed palm civet (Arctogalidia trivirgata) and asian palm civet (Paradoxurus hermaphroditus). Population density of each species from the highest to the lowest is 13,5 Individual of leopard cat/km2, 9,84 Individual of malayan sun bears/km2, 4,31 Individual of sunda clouded leopard/km2, and 3,65 Individual of civet/km2. Malayan sun bears, sunda clouded leopards and civets prefer to be in land forest. Leopard cats prefers to be in transition forest.

scholarly journals Performance of Parametric Model for Line Transect Data

2020 ◽  
pp. 1-7
Author(s):  
Noryanti Muhammad ◽  
Gamil A.A. Saeed ◽  
Wan Nur Syahidah Wan Yusoff
Keyword(s):  
Simulation Study ◽  
Present Model ◽  
Parametric Model ◽  
Line Transect ◽  
Population Abundance ◽  
Line Transect Sampling ◽  
Detection Function ◽  
Transect Sampling ◽  
Proposed Model ◽  
Shoulder Condition

One of the most important sides of life is wildlife. There is growing research interest in monitoring wildlife. Line transect sampling is one of the techniques widely used for estimating the density of objects especially for animals and plants. In this research, a parametric estimator for estimation of the population abundance is developed. A new parametric model for perpendicular distances for detection function is utilised to develop the estimator. In this paper, the performance of the parametric model which was developed using a simulation study is presented. The detection function has non-increasing curve and a perfect probability at zero. Theoretically, the parametric model which has been developed is guar-anteed to satisfy the shoulder condition assumption. A simulation study is presented to validate the present model. Relative mean error (RME) and Relative Bias (RB) are used to compare the estimator with well-known existing estimators. The results of the simulation study are discussed, and the performance of the proposed model shows promising statistical properties which outperformed the existing models. Keywords: detection function, line transect data, parametric model

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