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Final Report - New York State Marsh Bird Monitoring Program Pilot Study 2009 - 2011

American bittern by Matthew Walters
American bittern by Matthew Walters

Population status and trends remain uncertain for many marsh bird species due to their elusive behavior, infrequent vocalizations, and affinity for inaccessible emergent wetlands. These traits make it difficult to detect marsh birds during traditional surveys, limiting the ability of existing long-term, wide-scale bird monitoring programs to estimate marsh bird trends. A targeted marsh bird survey protocol has been developed to increase detection rates, however, inconsistencies among sampling designs precludes pooling of data from multiple locations which is necessary to understand marsh birds at regional or continental scales. To address this issue, New York State Department of Environmental Conservation (NYSDEC) was one of seven other states that participated in the U.S. Fish and Wildlife Service's (USFWS) National Marsh Bird Monitoring Program Pilot Study, which integrated a statistically rigorous sampling design with the Standardized North American Marsh Bird Monitoring Protocols to assess the population status of secretive marsh birds. Focal species included Virginia rail, sora, king rail, American bittern, least bittern and pied-billed grebe. Primary objectives of the three-year pilot study in NY included: (1) to estimate temporal trends in marsh bird occupancy and abundance to inform management decisions regarding population health; (2) to determine change in annual occupancy and abundance to inform regulatory decisions for harvested species; and (3) to document species-specific habitat associations at multiple scales.

From 2009 to 2011, NYSDEC conducted nearly 1,500 call-broadcast surveys at 417 survey points in freshwater wetlands throughout upstate NY and one freshwater wetland on Long Island. Survey points included random points from the pilot study sampling design (n=366) as well as non-random long-term monitoring points (n=51) previously established by NYSDEC. We calculated species-specific weighted model averages of maximum likelihood estimates (MLEs) of site occupancy probability as an index of population status, and compared habitat characteristics at detection and non-detection sites. Including both pilot study and long-term monitoring points, Virginia rail was the most frequently observed focal species with detections at 23% of the survey points (n=94). Occupancy MLEs were 0.133 in 2009, 0.305 in 2010, and 0.317 in 2011. Virginia rail were detected at sites with more emergent and floating vegetation, more open water, and less shrubs and upland habitat than nondetection sites. American bittern were detected at 10% of survey points (n=42). Occupancy MLEs were 0.042 in 2009, 0.198 in 2010, and 0.293 in 2011 and top-supported models indicated that detection probability was survey-dependent. American bittern were detected at sites with greater water depth, more open water and floating vegetation, less shrub cover, less upland habitat than nondetection sites. Pied-billed grebe were detected at 9% of points (n=39) and occupancy MLEs were 0.006 in 2009, 0.170 in 2010, and 0.159 in 2011. Detection sites had less emergent vegetation and more open water than nondetection sites. Least bittern were detected at 8% of points (n=33) and occupancy MLEs were 0.078 in 2009, 0.149 in 2010, and 0.175 in 2011. Detection sites had deeper and more open water than nondetection sites. Sora were detected at 7% of points (n=30). Occupancy MLEs were 0.136 in 2009, 0.268 in 2010, and 0.215 in 2011 and detection points had slightly more floating vegetation than nondetection sites. King rail were detected at <1% of points (n=3) with a naïve site occupancy of ≤ 0.01 in all years; estimates of occupancy and detection probabilities could not be modeled with such sparse detection histories. In order to gain a better understanding of statewide marsh bird trends, a sustained or increased intensity of future survey efforts will be required.

The final report from this study entitled New York State Marsh Bird Monitoring Program Pilot Study 2009 - 2011(PDF, 980 KB) is available by following the link in the right hand column of this page. The Table of Contents is provided below.

TABLE OF CONTENTS

Summary

Table of Contents

Acknowledgements

Introduction

Methods

Sampling design

Study area

Survey protocols

Statistical analysis

Results and Discussion

Focal species detections

Occupancy (ψ) and detection (p) maximum likelihood estimates

Habitat covariates at detection vs. non-detection points

Pilot study considerations

Transitioning to long-term monitoring program

Literature Cited

Appendix A - NYS Marsh Bird Monitoring Program survey routes, 2009-2011

Appendix B - Model averaged maximum likelihood estimates of occupancy and detection probabilities

Appendix C - Frequency of focal species detection/nondetection among vegetation height and density classes