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 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.

Change-in-ratio density estimator for feral pigs is less biased than closed mark - recapture estimates

2008 ◽  
Vol 35 (7) ◽  
pp. 695 ◽  
Author(s):  
Laura B. Hanson ◽  
James B. Grand ◽  
Michael S. Mitchell ◽  
D. Buck Jolley ◽  
Bill D. Sparklin ◽  
...  
Keyword(s):  
Estimation Method ◽  
Density Estimator ◽  
Density Estimates ◽  
Mark Recapture ◽  
Closed Population ◽  
Feral Pigs ◽  
Open Population ◽  
Detection Probabilities ◽  
Models Comparison

Closed-population capture–mark–recapture (CMR) methods can produce biased density estimates for species with low or heterogeneous detection probabilities. In an attempt to address such biases, we developed a density-estimation method based on the change in ratio (CIR) of survival between two populations where survival, calculated using an open-population CMR model, is known to differ. We used our method to estimate density for a feral pig (Sus scrofa) population on Fort Benning, Georgia, USA. To assess its validity, we compared it to an estimate of the minimum density of pigs known to be alive and two estimates based on closed-population CMR models. Comparison of the density estimates revealed that the CIR estimator produced a density estimate with low precision that was reasonable with respect to minimum known density. By contrast, density point estimates using the closed-population CMR models were less than the minimum known density, consistent with biases created by low and heterogeneous capture probabilities for species like feral pigs that may occur in low density or are difficult to capture. Our CIR density estimator may be useful for tracking broad-scale, long-term changes in species, such as large cats, for which closed CMR models are unlikely to work.

Conventional distance sampling versus strip transects and abundance indices for estimating abundance of greater gliders (Petauroides volans) and eastern ringtail possums (Pseudocheirus peregrinus)

2019 ◽  
Vol 46 (6) ◽  
pp. 518
Author(s):  
Luke D. Emerson ◽  
Guy-Anthony Ballard ◽  
Karl Vernes
Keyword(s):  
Distance Sampling ◽  
Probability Of Detection ◽  
Density Estimate ◽  
Imperfect Detection ◽  
Density Estimates ◽  
Transect Line ◽  
Eucalypt Forest ◽  
Arboreal Marsupials ◽  
Abundance Indices ◽  
Strip Transect

Abstract ContextAccurate estimates of abundance are extremely useful for wildlife management and conservation. Estimates generated from distance sampling are typically considered superior to strip transects and abundance indices, as the latter do not account for probability of detection, thereby risking significant error. AimTo compare density estimates generated from conventional distance sampling (CDS) of arboreal marsupials with strip transect density estimates and abundance indices. MethodsOff-track CDS and strip transects were used to estimate densities of P. volans and P. peregrinus across ~2.6km2 of remnant eucalypt forest at Mt Duval in north-eastern New South Wales. Key resultsCDS density estimates for P. volans (1.36ha−1, 95% confidence interval (CI) of 1.07–1.72ha−1) and P. peregrinus (0.28ha−1, 95% CI 0.22–0.35ha−1) were consistent with densities reported in other studies conducted in open eucalypt forests. A strip transect width of 40m for P. volans resulted in a collective set of values for density (1.35ha−1), error (s.e.±0.14), precision (cv 0.10) and 95% CI (1.07–1.62ha−1) closest to those associated with the CDS-generated density estimate (1.36ha−1, s.e.±0.15, cv 0.10, 95% CI 1.07–1.72ha−1). Strip widths of 10 to 40m resulted in density estimates for P. peregrinus closest to those generated through CDS, but much less precise. ConclusionsAlthough a 40-m wide strip transect provided a robust density estimate for P. volans at Mt Duval, this is unlikely to be consistent across different study areas. Strip transects provided less precise density estimates, or underestimated P. peregrinus density at Mt Duval, when compared with CDS density estimates. CDS should be favoured over strip transects or abundance indices for estimating P. volans and P. peregrinus abundance, because it is capable of providing more meaningful and robust abundance estimates by accounting for the probability of detection from the transect line across different habitats. ImplicationsResearchers, conservation managers and decision makers should be aware that common methods for assessing arboreal marsupial abundance have serious potential weaknesses. Thus, it would be prudent to invest in studies that address imperfect detection to improve the quality of monitoring data.

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.

scholarly journals Seabirds At-Sea Surveys: The Line-Transect Method Outperforms the Point-Transect Alternative

2017 ◽  
Vol 10 (1) ◽  
pp. 42-52 ◽  
Author(s):  
François Bolduc ◽  
David A. Fifield
Keyword(s):  
Detection Probability ◽  
Goodness Of Fit ◽  
Probability Of Detection ◽  
Line Transect ◽  
Density Estimates ◽  
Coefficients Of Variation ◽  
Line Transects ◽  
Point Transect ◽  
Line Transect Method ◽  
Seabirds At Sea

Introduction:Knowledge of seasonal distribution and abundance of species is paramount in identifying key areas. Field data collection and analysis must provide best information concerning seabirds at-sea to optimize conservation efforts.Methods:We tested whether modeling of detection probabilities, and density estimates with their coefficients of variation obtained from the point-transect method provided more robust and precise results than the more commonly used line-transect method. We subdivided our data by species groups (alcids, and aerialist species), and into two behavior categories (flyingvs.swimming). We also computed density estimates from the strip-transect and point count methods, to relate differences between transect methods to their counterparts that do not consider a decreasing probability of detection with distance from the observer. We used data collected in the Gulf of St. Lawrence between 2009 and 2010 when observers simultaneously conducted line- and point-transect sampling.Results:Models of detection probability using the line-transect method had a good fit to the observed data, whereas detection probability histograms of point-transect analyses suggested substantial evasive movements within the 0-50 m interval. This resulted in point-transect detection probability models displaying poor goodness of fit. Line transects yielded density estimates 1.2-2.6 times higher than those obtained using the point-transect method. Differences in percent coefficients of variation between line-transect and point-transect density estimates ranged between 0.2 and 5.9.Conclusion:Using 300 m wide line-transects provided the best results, while other methods could lead to biased conclusions regarding species density in the local landscape and the relative composition of seabird communities among species and behavior groups.

Theory and application of mark - recapture and related techniques to aerial surveys of wildlife

2008 ◽  
Vol 35 (4) ◽  
pp. 268 ◽  
Author(s):  
Richard Barker
Keyword(s):  
Conditional Independence ◽  
Survey Design ◽  
Imperfect Detection ◽  
Mark Recapture ◽  
Closed Population ◽  
Aerial Surveys ◽  
Detection Probabilities ◽  
Complete Independence ◽  
Multiple Observer ◽  
Observer Studies

The key difficulty in assessing animal numbers from the air is that not all animals are seen by the observers. Methods for estimating detection probabilities, or accounting for imperfect detection, are reviewed including double surveys, use of sightability models, mark–resight, and mark–recapture. The assumptions needed for each method are considered as well as issues concerning survey design. For closed-population mark–recapture modelling particular attention is given to multiple observer studies. An emphasis is that an assumption of complete independence in double-observer studies is rarely justifiable and that independent observers will generally only satisfy an assumption of conditional independence and not complete independence.

scholarly journals Variability in Grassland Bird Counts Related to Observer Differences and Species Detection Rates

The Auk ◽  
2003 ◽  
Vol 120 (4) ◽  
pp. 1168-1179 ◽  
Author(s):  
Duane R. Diefenbach ◽  
Daniel W. Brauning ◽  
Jennifer A. Mattice
Keyword(s):  
Survey Methods ◽  
Distance Sampling ◽  
Monitoring Program ◽  
Detection Rates ◽  
Species Detection ◽  
Point Counts ◽  
Grasshopper Sparrow ◽  
Transect Line ◽  
Detection Probabilities ◽  
Henslow's Sparrow

Abstract Differences among observers in ability to detect and identify birds has been long recognized as a potential source of error when surveying terrestrial birds. However, few published studies address that issue in their methods or study design. We used distance sampling with line transects to investigate differences in detection probabilities among observers and among three species of grassland songbirds: Henslow's Sparrow (Ammodramus henslowii), Grasshopper Sparrow (A. savannarum), and Savannah Sparrow (Passerculus sandwichensis). Our review of 75 papers published in 1985–2001 found that the most commonly used methods were fixed-width transects (31%, 23 papers) and fixed-radius point counts (20%, 15 papers). The median half-width of fixed-width strip transects used by researchers was 50 m, but our results indicated detection probabilities were <1.0 at distances >25 m for most observers and species. Beyond 50 m from the transect line, we found that as many as 60% of birds were missed by observers and that the proportion missed differed among observers and species. Detection probabilities among observers ranged from 0.43 to 1.00 for Henslow's Sparrow, from 0.44 to 0.66 for Grasshopper Sparrow, and from 0.60 to 0.72 for Grasshopper Sparrow for birds detected within 58–100 m of the transect line. Using our estimates of detection probabilities for Henslow's Sparrows among six observers in a computer simulation of a monitoring program, we found that bird counts from fixed-width transects required an additional 2–3 years of monitoring to detect a given decline in abundance compared to density estimates that used a method to correct for missed birds. We recommend that researchers employ survey methods that correct for detection probabilities <1.0.

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.

Correcting wildlife counts using detection probabilities

2005 ◽  
Vol 32 (3) ◽  
pp. 211 ◽  
Author(s):  
Gary C. White
Keyword(s):  
Detection Probability ◽  
Distance Sampling ◽  
Probability Of Detection ◽  
Mark Recapture ◽  
Additional Information ◽  
Release Studies ◽  
Detection Probabilities ◽  
Minimum Number ◽  
Capture And Release ◽  
Wildlife Populations

One of the most pervasive uses of indices of wildlife populations is uncorrected counts of animals. Two examples are the minimum number known alive from capture and release studies, and aerial surveys where the detection probability is not estimated from a sightability model, marked animals, or distance sampling. Both the mark–recapture and distance-sampling estimators are techniques to estimate the probability of detection of an individual animal (or cluster of animals), which is then used to correct a count of animals. However, often the number of animals in a survey is inadequate to compute an estimate of the detection probability and hence correct the count. Modern methods allow sophisticated modelling to estimate the detection probability, including incorporating covariates to provide additional information about the detection probability. Examples from both distance and mark–recapture sampling are presented to demonstrate the approach.

Mark‐Recapture Distance Sampling for Aerial Surveys of Ungulates on Rangelands

2020 ◽  
Vol 44 (4) ◽  
pp. 713-723
Author(s):  
Mary K. Peterson ◽  
Aaron M. Foley ◽  
Andrew N. Tri ◽  
David G. Hewitt ◽  
Randy W. DeYoung ◽  
...  
Keyword(s):  
Distance Sampling ◽  
Mark Recapture ◽  
Aerial Surveys
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