Abundance or population size - number of individual animals
Population density - number of individuals per unit area (e.g., 1.2 squirrels/ha)
Relative density - ranking of populations by density
Census - complete count of an entire population
Population estimate - an approximation of the true population size based on some method of sampling or modeling. A robust population estimate is still close to the true population size even if some of the assumptions of the estimation procedure are violated.
Index - constant but unknown relationship between true abundance and the value of the index.
Expected value - The average population estimate if the estimation procedure was performed many times under exactly the same conditions. The expected population estimate is represented by E(N).
Accuracy - Measure of how close a population estimate is to the true population size
Bias - Difference between the expected value of a population estimate and the true population size
Precision or Variance - Measure of how close population estimates are to the expected (NOT the true) value
A good estimate is BOTH unbiased and low variance
Population closure - An assumption for many estimation procedures that the population does not change during the estimation procedure. There are 2 components:
demographic closure - no births or deaths
geographic closure - no immigration or emigration
Total counts
Territory/Spot Mapping
Aerial Photography
Snorkeling
Total Counts on Sample Plots
Total counts may be possible on sample plots of a larger area of interest
see Survey Sampling
All individuals not observed
All individuals not observed and survey on sample plots
B. Popular Methods for Estimating Abundance
Distance estimation
Variable circular plot
Removal Methods (Catch-per-effort, Change-in-ratio)
Capture-Recapture
Aerial Survey
**Key to population estimation methods**
General References:
Caughley, G. 1977. Analysis of vertebrate populations. John Wiley and Sons, New York. 234pp. Chapters 4 and 10.
Conner, R. N., J. G. Dickson, and J. H. Williamson. 1983. A comparison of breeding bird census techniques with mist netting results. Wilson Bull. 95:276-280.
Krebs, C. J. 1989. Ecological methodology. Harper and Row, Publ., New York. 654pp.
Lancia, R. A., J. D. Nichols, and K. H. Pollock. 1994. Estimating the number of animals in wildlife populations. Pages 215-253 in T. A. Bookhout, ed. Research and management techniques for wildlife and habitats. Fifth ed. The Wildlife Society, Bethesda, Md.
Overton, W. S. 1971. Estimating the numbers of animals in wildlife populations. pp. 403-456 in Giles, R. H., Jr. (ed.). Wildlife management techniques. The Wildlife Society, Washington, D.C. 633pp.
Ralph, C. J., and J. M. Scott. (eds.). 1981. Estimating numbers of terrestrial birds. Studies in Avian Biology No. 6. Allen Press Inc., Lawrence, Kansas. 630pp.
Ricker, W. E. 1975. Computation and interpretation of biological statistics of fish populations. Department of the Environment Fisheries and Marine Service, Ottawa. 382pp.
Seber, G. A. F. 1982. The estimation of animal abundance and related parameters, 2nd edition. Charles Griffin and Co., London.
Line Transect and Strip Census:
Anderson, D. R., J. L. Laake, B. R. Crain, and K. P. Burnham. 1979. Guidelines for line transect sampling of biological populations. J. Wildl. Manage. 43:70-78.
Anderson, D. R., K. P. Burnham, G. C. White, and D. L. Otis. 1983. Density estimation of small mammal populations using a trapping web and distance sampling methods. Ecology 64:674-680.
Anderson, D. R., and R. S. Pospahala. 1970. Correction of bias in belt transect studies of immobile objects. J. Wildl. Manage. 34(1):141-146.
Buckland, S. T., D. R. Anderson, K. P. Burnham, and J. L. Lake. 1993. Distance sampling: estimating abundance of biological populations. Chapman and Hall, London.
Burnham, K. P., D. R. Anderson, and J. L. Laake. 1980. Estimation of density from line transect sampling of biological populations. J. Wildl. Manage. 72. 202pp.
Eberhardt, L. L. 1978. Transect methods for population studies. J. Wildl. Manage. 42(1):1-31.
Emlen, J. T. 1971. Population densities of birds derived from transect counts. Auk 88:323-342.
Emlen, J. T. 1977. Estimating breeding season bird densities from transect counts. Auk 94:455-468.
Gates, C. E., W. H. Marshall, and D. P. Olson. 1968. Line transect method of estimating grouse population densities. Biometrics 24:135-145.
Hayne, D. C. 1949. An examination of the strip census method for estimating animal populations. J. Wildl. Manage. 13(2):145-157.
Robinette, W. L., C. Loveless, and D. A. Jones. 1974. Field tests of strip census methods. J. Wildl. Manage. 38(1):81-96.
Wilson, K. R. 1983. Evaluation of a new trapping web design and analysis method for estimating density of small mammal populations. Unpub. M.S. Thesis, Utah State Univ., Logan, Utah. 88pp.
Mark-Recapture:
Arnason, A. N., and L. Baniuk. 1980. A computer system for mark-recapture analysis of open populations. J. Wildl. Manage. 44:325-332.
Bishop, J. A., and P. M. Sheppard. 1973. An evaluation of two capture-recapture models using the technique of computer simulation. pp. 235-251 in Bartlett, M. S. and R. W. Hiorns (eds.). The mathematical theory of the dynamics of biological populations. Academic Press, New York. 347pp.
Cormack, R. M. 1973. Common sense estimates from capture-recapture studies. pp. 225-234 in Bartlett, M. S. and R. W. Hiorns (eds.). The mathematical theory of the dynamics of biological populations. Academic Press, New York. 347pp.
Jolly, G. M. 1965. Explicit estimates from capture-recapture data with death and immigration-stochastic model. Biometrika 52(1):225-247.
_____. 1982. Mark-recapture models with parameters constant in time. Biometrics 38:301-321.
Otis, D. L., K. P. Burnham, G. C. White, and D. R. Anderson. 1978. Statistical inference from capture data on closed animal populations. Wildl. Manage. No. 62. 135pp.
Otis, D. L., K. P. Burnham, G. C. White, and D. R. Anderson. 1980. Corrections to Wildlife Monograph 62. J. Wildl. Manage. 44:666-667.
Pollock, K. H. 1982. A capture-recapture sampling design robust to unequal catchability. J. Wildl. Manage. 46:752-757.
_____, J. D. Nichols, C. Brownie, and J. E. Hines. 1990. Statistical inference for capture-recapture experiments. Wildl. Monogr. 107. 97pp.
Schnabel, Z. E. 1938. Estimation of the total fish population of a lake. Amer. Math. Monthly 45:348-352.
Schumacher, F. X., and R. W. Eschmeyer. 1943. The estimate of fish populations in lakes or ponds. J. Tenn. Acad. Sci. 18:228-249.
White, G. C., D. R. Anderson, K. P. Burnham, and D. L. Otis. 1982. Capture-recapture and removal methods for sampling closed populations. Report LA-8787-NERP, Los Alamos National Laboratory, Los Alamos, New Mexico. 235pp.
Spot Mapping:
Best, L. B. 1975. Interpretational errors in the "Mapping Method" as a census technique. Auk 92:452-460.
International Bird Census Committee. 1970. Recommendations for a mapping method in bird census work. Aud. Field Notes 24:722-726.
Kendeigh, S. C. 1944. Measurement of bird populations. Ecol. Monogr. 14:67-106.
Plot Size:
Eberhardt, L., and R. C. Van Etten. 1956. Evaluation of the pellet-group count as a deer census method. J. Wildl. Manage. 20:70-74.
Robinette, W. L., R. B. Ferguson, and J. S. Gashwiler. 1958. Problems involved in the use of deer pellet-group counts. Trans. N. Am. Wildl. Conf. 23:411-425.
Van Etten, R. C., and C. L. Bennett, Jr. 1965. Some sources of error in using pellet-group counts for censusing deer. J. Wildl. Manage. 29:723-729.
White, G. C., and L. E. Eberhardt. 1980. Statistical analysis of deer and elk pellet-group data. J. Wildl. Manage. 44:121-131.
Indices to Wildlife Abundance:
Braun, C. E., R. K. Schmidt, Jr., and G. E. Rogers. 1973. Census of Colorado white-tailed ptarmigan with tape-recorded calls. J. Wildl. Manage. 37:90-93.
Davis, J. 1965. The "Singing Male" method of censusing birds: a warning. Condor 67:86-87.
Freddy, D. J., and D. C. Bowden. 1983. Sampling mule deer pellet-group densities in juniper-pinyon woodland. J. Wildl. Manage. 47:476-485.
Gates, J. M. 1966. Crowing counts as indices to cock pheasant populations in Wisconsin. J. Wildl. Manage. 30:735-744.
Harrington, F. H., and L. D. Mech. 1982. An analysis of howling response parameters useful for wolf pack censusing. J. Wildl. Manage. 46:686-693.
Kimball, J. W. 1949. The crowing count pheasant census. J. Wildl. Manage. 13:101-120.
Linhart, S. B., and F. F. Knowlton. 1975. Determining the relative abundance of coyotes by scent station lines. Wildl. Soc. Bull. 3:119-124.
Neff, D. J. 1968. The pellet-group count technique for big game trend, census, and distribution: a review. J. Wildl. Manage. 32:597-614.
Newman, D. E. 1959. Factors influencing the winter roadside count of cottontails. J. Wildl. Manage. 23:290-294.
Parr, D. E., and M. D. Scott. 1978. Analysis of roosting counts as an index to wood duck population size. Wilson Bull. 90:423-437.
Rodgers, R. D. 1981. Factors affecting ruffed grouse drumming counts in southwestern Wisconsin. J. Wildl. Manage. 45:405-418.
Roughton, R. D., and M. W. Sweeny. 1982. Refinements in scent-station methodology for assessing trends in carnivore populations. J. Wildl. Manage. 46:217-229.