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 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

Evaluation of line-transect sampling for estimating koala abundance in the Pine Rivers Shire, south-east Queensland

2003 ◽  
Vol 30 (2) ◽  
pp. 127 ◽  
Author(s):  
David S. Dique ◽  
Deidré L. de Villiers ◽  
Harriet J. Preece
Keyword(s):  
Confidence Interval ◽  
Distance Sampling ◽  
Line Transect ◽  
Similar Estimate ◽  
Line Transect Sampling ◽  
Detection Function ◽  
Pilot Survey ◽  
Transect Sampling ◽  
Line Transects ◽  
Urban Sites

Distance sampling using line transects has not been previously used or tested for estimating koala abundance. In July 2001, a pilot survey was conducted to compare the use of line transects with strip transects for estimating koala abundance. Both methods provided a similar estimate of density. On the basis of the results of the pilot survey, the distribution and abundance of koalas in the Pine Rivers Shire, south-east Queensland, was determined using line-transect sampling. In total, 134 lines (length 64 km) were used to sample bushland areas. Eighty-two independent koalas were sighted. Analysis of the frequency distribution of sighting distances using the software program DISTANCE enabled a global detection function to be estimated for survey sites in bushland areas across the Shire. Abundance in urban parts of the Shire was estimated from densities obtained from total counts at eight urban sites that ranged from 26 to 51 ha in size. Koala abundance in the Pine Rivers Shire was estimated at 4584 (95% confidence interval, 4040–5247). Line-transect sampling is a useful method for estimating koala abundance provided experienced koala observers are used when conducting surveys.

Comparison of Helicopter Line Transects with Walked Line Transects for Estimating Densities of Kangaroos

1997 ◽  
Vol 24 (4) ◽  
pp. 397 ◽  
Author(s):  
T. F. Clancy ◽  
A. R. Pople ◽  
L. A. Gibson
Keyword(s):  
Repeated Measures ◽  
Aerial Survey ◽  
Survey Method ◽  
Line Transect ◽  
Attractive Alternative ◽  
Line Transect Sampling ◽  
Density Estimates ◽  
Transect Sampling ◽  
Grey Kangaroo ◽  
Line Transects

The performance of helicopter surveys for estimating population densities of red kangaroos (Macropus rufus), eastern grey kangaroos (Macropus giganteus) and common wallaroos (Macropus robustus) was investigated by comparing line-transect density estimates obtained from helicopter surveys with those from ground (walked) surveys. Comparisons were made at four sites in central western Queensland (areas with high densities of red kangaroos and common wallaroos) that were surveyed during winter and summer from December 1991 until February 1995, and one site in south-eastern Queensland (an area of high eastern grey kangaroo density) surveyed annually during autumn from March 1991 until March 1994. Helicopter surveys generally recorded lower sample sizes than did ground surveys (means ± s.e = 34 ± 6%, 33 ± 9% and 76 ± 2% lower for red kangaroos, eastern grey kangaroos and wallaroos, respectively). Density estimates obtained from the helicopter surveys were not significantly different from those obtained from ground surveys for both red and eastern grey kangaroos as assessed by repeated-measures ANOVA and regression analysis. However, helicopter surveys of common wallaroos consistently returned density estimates about half those of ground surveys. The relationships between the two methods did not differ between winter and summer for any species. The conventional aerial survey method for kangaroos of strip transects from fixed-wing aircraft has limited ability to adjust for varying sightability conditions. Therefore, helicopter surveys with line-transect sampling are an attractive alternative.

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.

Coping with variation in aerial survey protocol for line-transect sampling

2008 ◽  
Vol 35 (4) ◽  
pp. 289 ◽  
Author(s):  
Jeff Laake ◽  
Richard J. Guenzel ◽  
John L. Bengtson ◽  
Peter Boveng ◽  
Michael Cameron ◽  
...  
Keyword(s):  
Aerial Survey ◽  
Line Transect ◽  
Antilocapra Americana ◽  
Line Transect Sampling ◽  
Transect Sampling ◽  
Sources Of Variation ◽  
Distance Data ◽  
Biased Estimators ◽  
Using Data ◽  
Survey Protocol

Altitude and flight speed affect detection probability and they typically vary during the course of most aerial surveys. We demonstrate how these sources of variation can be accommodated with covariates in a line-transect analysis using data from a pronghorn (Antilocapra americana) survey in Wyoming and a survey of Antarctic ice seals (Lobodon carcinophaga, Leptonychotes weddellii, Hydrurga leptonyx, Ommatophoca rossii). We also show how the likelihood for binned distance data can be modified to allow for variation in altitude. As an alternative, we develop an estimator for aerial line-transect sampling based on vertical angles rather than distance. With a small simulation study, we show that our estimators are unbiased and are preferable to using biased estimators based on fixed-distance intervals derived from average altitude.

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.

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 Double Kernel Method Using Line Transect Sampling

2016 ◽  
Vol 41 (2) ◽  
Author(s):  
Omar Eidous ◽  
M.K. Shakhatreh
Keyword(s):  
Kernel Method ◽  
Kernel Estimator ◽  
Real Data ◽  
Line Transect ◽  
Population Abundance ◽  
Line Transect Sampling ◽  
Numerical Examples ◽  
Bootstrap Techniques ◽  
Transect Sampling ◽  
Kernel Type

A double kernel method as an alternative to the classical kernel method is proposed to estimate the population abundance by using line transect sampling. The proposed method produces an estimator that is essentially a kernel type of estimator use the kernel estimator twice to improve the performances of the classical kernel estimator. The feasibility of using bootstrap techniques to estimate the bias and variance of the proposed estimator is also addressed. Some numerical examples based on simulated and real data are presented. The results show that the proposed estimator outperforms existingclassical kernel estimator in most considered cases.

Line Transect Sampling

2006 ◽  
Author(s):  
E. C. Pielou
Keyword(s):  
Line Transect ◽  
Line Transect Sampling ◽  
Transect Sampling
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