Detecting population decline of birds using long-term monitoring data |
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Authors: | Ikuko Fujisaki Elise V Pearlstine Mark Miller |
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Institution: | (1) Department of Ecosystem Science and Management, Texas A&M University, 2138 TAMU, College Station, TX 77843-2138, USA;(2) Everglades Research and Education Center, University of Florida, 3200 East Palm Beach Road, Belle Glade, FL 33430-4702, USA;(3) Ft. Lauderdale Research and Education Center, University of Florida, 3205 College Ave, Davie, FL 33314, USA |
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Abstract: | Abrupt population change in birds may be caused by various factors. When such events occur, it is important to understand
the population-level impact on the species. We applied a change point analysis with Markov chain Monte Carlo using long-term
population count data to address this question. We first investigated the method with a simple Poisson model using synthetic
data sets for different population decline scenarios and number of observations. Estimated change points were particularly
accurate when a large decline in counts occurred. Accuracy and precision of posterior change magnitude tended to increase
when actual change magnitude became larger. We applied the method to two cases using data from the North American Breeding
Bird Survey: epidemic mortality of Florida scrub-jays (Aphelocoma coerulescens) in central Florida and population decline of American crows (Corvus brachyrhynchos) in Maryland and Virginia after West Nile virus emergence. The Florida scrub-jay case study indicated that the estimated
change point was accurate compared with that reported by local monitoring. A Poisson-log model that included observer and
year variability resulted in better fit to the data than a simple Poisson model. The American crow case study showed that
the method detected change points towards the end of observational data, but not all change point parameters converged, which
may suggest that a population decline did not occur or was small for some survey routes we analyzed. Our study demonstrates
the utility of change point analysis to examine abrupt population change. Data from systematic long-term monitoring can be
a basis of such an analysis. |
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Keywords: | Bayesian Change point analysis Markov chain Monte Carlo North American Breeding Bird Survey Population monitoring |
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