William Link, Ph.D. (Former Employee)
Science and Products
Filter Total Items: 44
No results found.
Filter Total Items: 122
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 consequences of betw
Authors
J.R. Sauer, B.G. Peterjohn, W. A. Link
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 altern
Authors
W. A. Link, J.R. Sauer
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 traditional
Authors
G. M. Haramis, E.L. Derleth, W. A. Link
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 from the
Authors
W. A. Link, R. J. Barker
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 series
Authors
W. A. Link, J. D. Nichols
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 trends
Authors
B.G. Peterjohn, J.R. Sauer, W. A. Link
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 parameters
Authors
William A. Link
Efficiency and optimal allocation in the staggered entry design
The staggered entry design for survival analysis specifies that r left-truncated samples are to be used in estimation of a population survival function. The ith sample is taken at time Bi, from the subpopulation of individuals having survival time exceeding Bi. This paper investigates the performance of the staggered entry design relative to the usual design in which all samples have a common t
Authors
W. A. Link
The detection of density-dependence from a series of annual censuses: A comment
No abstract available.
Authors
William A. Link, B. A. Hoover
Power calculations and model selection for trend analysis: A comment
No abstract available.
Authors
William A. Link, Jeff S. Hatfield
Social foraging and feeding environment of the black-crowned night heron in an industrialized estuary
A nesting colony of more than 300 pairs of Black-crowned Night-Herons in the Patapsco River estuary, Baltimore Harber, Maryland was monitored from May to July 1988. The departure direction and departure time of each Heron was recorded during mornjng and evening observations at the colony. In addition, individual Herons were followed to landing sites in the estuary with small boats and aircraft.
Authors
R. Michael Erwin, J. S. Hatfield, William A. Link
Response to Dufour and Ankney
No abstract available.
Authors
D.G. Krementz, R. J. Barker, W. A. Link, J. E. Hines, P.O. Corr, R.B. Owen
Science and Products
Filter Total Items: 44
No results found.
Filter Total Items: 122
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 consequences of betw
Authors
J.R. Sauer, B.G. Peterjohn, W. A. Link
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 altern
Authors
W. A. Link, J.R. Sauer
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 traditional
Authors
G. M. Haramis, E.L. Derleth, W. A. Link
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 from the
Authors
W. A. Link, R. J. Barker
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 series
Authors
W. A. Link, J. D. Nichols
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 trends
Authors
B.G. Peterjohn, J.R. Sauer, W. A. Link
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 parameters
Authors
William A. Link
Efficiency and optimal allocation in the staggered entry design
The staggered entry design for survival analysis specifies that r left-truncated samples are to be used in estimation of a population survival function. The ith sample is taken at time Bi, from the subpopulation of individuals having survival time exceeding Bi. This paper investigates the performance of the staggered entry design relative to the usual design in which all samples have a common t
Authors
W. A. Link
The detection of density-dependence from a series of annual censuses: A comment
No abstract available.
Authors
William A. Link, B. A. Hoover
Power calculations and model selection for trend analysis: A comment
No abstract available.
Authors
William A. Link, Jeff S. Hatfield
Social foraging and feeding environment of the black-crowned night heron in an industrialized estuary
A nesting colony of more than 300 pairs of Black-crowned Night-Herons in the Patapsco River estuary, Baltimore Harber, Maryland was monitored from May to July 1988. The departure direction and departure time of each Heron was recorded during mornjng and evening observations at the colony. In addition, individual Herons were followed to landing sites in the estuary with small boats and aircraft.
Authors
R. Michael Erwin, J. S. Hatfield, William A. Link
Response to Dufour and Ankney
No abstract available.
Authors
D.G. Krementz, R. J. Barker, W. A. Link, J. E. Hines, P.O. Corr, R.B. Owen