William Link, Ph.D. (Former Employee)
Science and Products
Filter Total Items: 44
No results found.
Filter Total Items: 128
The 1994 and 1995 summary of the North American Breeding Bird Survey The 1994 and 1995 summary of the North American Breeding Bird Survey
Data from the North American Breeding Bird Survey were used to estimate continental and regional changes in bird populations for the 2-year periods of 1993-1994 and 1994-1995. These 2-year changes were placed in the context of population trends estimated over the 1966-1995 interval. The 2-year changes were more positive during the 1993-1994 period, when 54.2% of all species exhibited...
Authors
B.G. Peterjohn, J.R. Sauer, W.A. Link
Estimation and confidence intervals for empirical mixing distributions Estimation and confidence intervals for empirical mixing distributions
Questions regarding collections of parameter estimates can frequently be expressed in terms of an empirical mixing distribution (EMD). This report discusses empirical Bayes estimation of an EMD, with emphasis on the construction of interval estimates. Estimation of the EMD is accomplished by substitution of estimates of prior parameters in the posterior mean of the EMD. This procedure is
Authors
W.A. Link, J.R. Sauer
Correcting for overdispersion in tests of prey selectivity Correcting for overdispersion in tests of prey selectivity
No abstract available.
Authors
W.A. Link, K. Karanth
The 1992 and 1993 summary of the North American Breeding Bird Survey The 1992 and 1993 summary of the North American Breeding Bird Survey
Using data from the North American Breeding Bird Survey (BBS), continental and regional changes in bird populations were estimated for the 2-year periods of 1991-1992 and 1992-1993. These 2-year changes were placed in the context of population trends since 1966. During 1991-1992, 62% of all species exhibited positive continental trend estimates. For species showing significant population...
Authors
B.G. Peterjohn, J.R. Sauer, W.A. Link
Estimating breeding proportions and testing hypotheses about costs of reproduction with capture-recapture data Estimating breeding proportions and testing hypotheses about costs of reproduction with capture-recapture data
The proportion of animals in a population that breeds is an important determinant of population growth rate. Usual estimates of this quantity from field sampling data assume that the probability of appearing in the capture or count statistic is the same for animals that do and do not breed. A similar assumption is required by most existing methods used to test ecologically interesting...
Authors
James D. Nichols, James E. Hines, Kenneth Pollock, Robert Hinz, William A. Link
Within-site variability in surveys of wildlife populations Within-site variability in surveys of wildlife populations
Most large-scale surveys of animal populations are based on counts of individuals observed during a sampling period, which are used as indexes to the population. The variability in these indexes not only reflects variability in population sizes among sites but also variability due to the inexactness of the counts. Repeated counts at survey sites can be used to document this additional...
Authors
William A. Link, Richard J. Barker, John R. Sauer, Sam Droege
Estimating equations estimates of trends Estimating equations estimates of trends
The North American Breeding Bird Survey monitors changes in bird populations through time using annual counts at fixed survey sites. The usual method of estimating trends has been to use the logarithm of the counts in a regression analysis. It is contended that this procedure is reasonably satisfactory for more abundant species, but produces biased estimates for less abundant species. An
Authors
W.A. Link, J.R. Sauer
Flock sizes and sex ratios of canvasbacks in Chesapeake Bay and North Carolina Flock sizes and sex ratios of canvasbacks in Chesapeake Bay and North Carolina
Knowledge of the distribution, size, and sex ratios of flocks of wintering canvasbacks (Aythya valisineria) is fundamental to understanding the species' winter ecology and providing guidelines for management. Consequently, in winter 1986-87, we conducted 4 monthly aerial photographic surveys to investigate temporal changes in distribution, size, and sex ratios of canvasback flocks in...
Authors
G. Michael Haramis, Eric Derleth, William A. Link
Density estimation using the trapping web design: A geometric analysis Density estimation using the trapping web design: A geometric analysis
Population densities for small mammal and arthropod populations can be estimated using capture frequencies for a web of traps. A conceptually simple geometric analysis that avoid the need to estimate a point on a density function is proposed. This analysis incorporates data from the outermost rings of traps, explaining large capture frequencies in these rings rather than truncating them...
Authors
W.A. Link, R. Barker
On the importance of sampling variance to investigations of temporal variation in animal population size On the importance of sampling variance to investigations of temporal variation in animal population size
Our purpose here is to emphasize the need to properly deal with sampling variance when studying population variability and to present a means of doing so. We present an estimator for temporal variance of population size for the general case in which there are both sampling variances and covariances associated with estimates of population size. We illustrate the estimation approach with a...
Authors
W.A. Link, J.D. Nichols
Observer differences in the North American Breeding Bird Survey Observer differences in the North American Breeding Bird Survey
Because count data collected in many bird surveys are only an index to population size, factors that can influence the counts must be identified and incorporated into analyses. Observer quality is often ignored in analyses of population changes from survey data, but observers differ in methods and capabilities and, hence, tend to count different numbers of birds. We assess the...
Authors
J.R. Sauer, B.G. Peterjohn, W.A. Link
Simulation testing of unbiasedness of variance estimators Simulation testing of unbiasedness of variance estimators
In this article I address the evaluation of estimators of variance for parameter estimates. Given an unbiased estimator X of a parameter θ, and an estimator V of the variance of X, how does one test (via simulation) whether V is an unbiased estimator of the variance of X? The derivation of the test statistic illustrates the need for care in substituting consistent estimators for unknown...
Authors
William Link
Science and Products
Filter Total Items: 44
No results found.
Filter Total Items: 128
The 1994 and 1995 summary of the North American Breeding Bird Survey The 1994 and 1995 summary of the North American Breeding Bird Survey
Data from the North American Breeding Bird Survey were used to estimate continental and regional changes in bird populations for the 2-year periods of 1993-1994 and 1994-1995. These 2-year changes were placed in the context of population trends estimated over the 1966-1995 interval. The 2-year changes were more positive during the 1993-1994 period, when 54.2% of all species exhibited...
Authors
B.G. Peterjohn, J.R. Sauer, W.A. Link
Estimation and confidence intervals for empirical mixing distributions Estimation and confidence intervals for empirical mixing distributions
Questions regarding collections of parameter estimates can frequently be expressed in terms of an empirical mixing distribution (EMD). This report discusses empirical Bayes estimation of an EMD, with emphasis on the construction of interval estimates. Estimation of the EMD is accomplished by substitution of estimates of prior parameters in the posterior mean of the EMD. This procedure is
Authors
W.A. Link, J.R. Sauer
Correcting for overdispersion in tests of prey selectivity Correcting for overdispersion in tests of prey selectivity
No abstract available.
Authors
W.A. Link, K. Karanth
The 1992 and 1993 summary of the North American Breeding Bird Survey The 1992 and 1993 summary of the North American Breeding Bird Survey
Using data from the North American Breeding Bird Survey (BBS), continental and regional changes in bird populations were estimated for the 2-year periods of 1991-1992 and 1992-1993. These 2-year changes were placed in the context of population trends since 1966. During 1991-1992, 62% of all species exhibited positive continental trend estimates. For species showing significant population...
Authors
B.G. Peterjohn, J.R. Sauer, W.A. Link
Estimating breeding proportions and testing hypotheses about costs of reproduction with capture-recapture data Estimating breeding proportions and testing hypotheses about costs of reproduction with capture-recapture data
The proportion of animals in a population that breeds is an important determinant of population growth rate. Usual estimates of this quantity from field sampling data assume that the probability of appearing in the capture or count statistic is the same for animals that do and do not breed. A similar assumption is required by most existing methods used to test ecologically interesting...
Authors
James D. Nichols, James E. Hines, Kenneth Pollock, Robert Hinz, William A. Link
Within-site variability in surveys of wildlife populations Within-site variability in surveys of wildlife populations
Most large-scale surveys of animal populations are based on counts of individuals observed during a sampling period, which are used as indexes to the population. The variability in these indexes not only reflects variability in population sizes among sites but also variability due to the inexactness of the counts. Repeated counts at survey sites can be used to document this additional...
Authors
William A. Link, Richard J. Barker, John R. Sauer, Sam Droege
Estimating equations estimates of trends Estimating equations estimates of trends
The North American Breeding Bird Survey monitors changes in bird populations through time using annual counts at fixed survey sites. The usual method of estimating trends has been to use the logarithm of the counts in a regression analysis. It is contended that this procedure is reasonably satisfactory for more abundant species, but produces biased estimates for less abundant species. An
Authors
W.A. Link, J.R. Sauer
Flock sizes and sex ratios of canvasbacks in Chesapeake Bay and North Carolina Flock sizes and sex ratios of canvasbacks in Chesapeake Bay and North Carolina
Knowledge of the distribution, size, and sex ratios of flocks of wintering canvasbacks (Aythya valisineria) is fundamental to understanding the species' winter ecology and providing guidelines for management. Consequently, in winter 1986-87, we conducted 4 monthly aerial photographic surveys to investigate temporal changes in distribution, size, and sex ratios of canvasback flocks in...
Authors
G. Michael Haramis, Eric Derleth, William A. Link
Density estimation using the trapping web design: A geometric analysis Density estimation using the trapping web design: A geometric analysis
Population densities for small mammal and arthropod populations can be estimated using capture frequencies for a web of traps. A conceptually simple geometric analysis that avoid the need to estimate a point on a density function is proposed. This analysis incorporates data from the outermost rings of traps, explaining large capture frequencies in these rings rather than truncating them...
Authors
W.A. Link, R. Barker
On the importance of sampling variance to investigations of temporal variation in animal population size On the importance of sampling variance to investigations of temporal variation in animal population size
Our purpose here is to emphasize the need to properly deal with sampling variance when studying population variability and to present a means of doing so. We present an estimator for temporal variance of population size for the general case in which there are both sampling variances and covariances associated with estimates of population size. We illustrate the estimation approach with a...
Authors
W.A. Link, J.D. Nichols
Observer differences in the North American Breeding Bird Survey Observer differences in the North American Breeding Bird Survey
Because count data collected in many bird surveys are only an index to population size, factors that can influence the counts must be identified and incorporated into analyses. Observer quality is often ignored in analyses of population changes from survey data, but observers differ in methods and capabilities and, hence, tend to count different numbers of birds. We assess the...
Authors
J.R. Sauer, B.G. Peterjohn, W.A. Link
Simulation testing of unbiasedness of variance estimators Simulation testing of unbiasedness of variance estimators
In this article I address the evaluation of estimators of variance for parameter estimates. Given an unbiased estimator X of a parameter θ, and an estimator V of the variance of X, how does one test (via simulation) whether V is an unbiased estimator of the variance of X? The derivation of the test statistic illustrates the need for care in substituting consistent estimators for unknown...
Authors
William Link