A field test of two methods for density estimation

Abstract Density of wildlife populations is a key variable for management, yet reliable estimation is elusive. We tested one established method (trapping webs and distance analysis) and one novel method (inverse prediction from capture–recapture data) on a population of brushtail possums (Trichosurus vulpecula) whose density also could be determined by exhaustive removal. The study area was approximately 315 ha of coastal plantation forest surrounded on 3 sides by sand and water. We placed 4 lines of 9 cage traps at 20-m spacing in a square to form a “hollow grid.” We set 5 hollow grids, each comprising 36 traps, for 5 days; we tagged and released possums. We later set 5 trapping webs of 50 traps each at the same sites; we caught possums and removed them over 4 days. Wide-area removal used a combination of acute poisoning and leghold trapping. The estimate of density by inverse prediction (1.88/ha, SE = 0.26) was consistent with the removal estimate (2.27/ha), whereas estimates from trapping webs were positively biased (6.5 to 8.0/ha, depending on method of analysis). The inverse prediction method frees capture–recapture from the straitjacket of conventional grids and should allow accurate landscape-scale estimation of density once the requisite trapping effort is identified.

[1]  M. Efford.  Density estimation in live‐trapping studies , 2004 .

[2]  C. S. Robbins,et al.  DENSITY: software for analysing capture-recapture data from passive detector arrays , 2004, Animal Biodiversity and Conservation.

[3]  W. Link.  Nonidentifiability of Population Size from Capture‐Recapture Data with Heterogeneous Detection Probabilities , 2003, Biometrics.

[4]  J. Andrew Royle,et al.  Mixture Models for Estimating the Size of a Closed Population When Capture Rates Vary among Individuals , 2003, Biometrics.

[5]  David R. Anderson,et al.  Small-mammal density estimation: A field comparison of grid-based vs. web-based density estimators , 2003 .

[6]  M. Conroy,et al.  Analysis and Management of Animal Populations , 2002 .

[7]  S. Pledger.  Unified Maximum Likelihood Estimates for Closed Capture–Recapture Models Using Mixtures , 2000, Biometrics.

[8]  A. Agresti,et al.  The Use of Mixed Logit Models to Reflect Heterogeneity in Capture‐Recapture Studies , 1999, Biometrics.

[9]  Shirley Pledger,et al.  CORRECTION OF BIAS DUE TO HETEROGENEOUS CAPTURE PROBABILITY IN CAPTURE-RECAPTURE STUDIES OF OPEN POPULATIONS , 1998 .

[10]  M. Conroy,et al.  Estimation of Density of Mongooses with Capture-Recapture and Distance Sampling , 1998 .

[11]  M. Efford.  Demographic consequences of sex‐biased dispersal in a population of brushtail possums , 1998 .

[12]  William A. Link,et al.  Density estimation using the trapping web design: A geometric analysis , 1994 .

[13]  A Chao,et al.  Estimating population size via sample coverage for closed capture-recapture models. , 1994, Biometrics.

[14]  A. Chao.  Estimating the population size for capture-recapture data with unequal catchability. , 1987, Biometrics.

[15]  James D. Nichols,et al.  A Field Comparison of Nested Grid and Trapping Web Density Estimators , 1987 .

[16]  David R. Anderson,et al.  Evaluation of a Density Estimator Based on a Trapping Web and Distance Sampling Theory , 1985 .

[17]  David R. Anderson,et al.  Evaluation of a nested grid approach for estimating density , 1985 .

[18]  David R. Anderson,et al.  Density estimation of small-mammal populations using a trapping web and distance sampling methods , 1983 .

[19]  David R. Anderson,et al.  Statistical inference from capture data on closed animal populations , 1980 .

[20]  K. Burnham,et al.  Estimation of the size of a closed population when capture probabilities vary among animals , 1978 .

[21]  R. Jennrich,et al.  Measurement of non-circular home range. , 1969, Journal of theoretical biology.

[22]  D. A. MacLulich.  A New Technique of Animal Census, with Examples , 1951 .

[23]  Paul M. Lukacs,et al.  WebSim: simulation software to assist in trapping web design , 2002 .

[24]  G. Seber,et al.  The Estimation of Animal Abundance , 1975 .