Date of Award

1-1-2012

Language

English

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College/School/Department

Department of Biological Sciences

Content Description

1 online resource (ix, 65 pages) : PDF file, color illustrations, color maps

Dissertation/Thesis Chair

George Robinson

Committee Members

Amielle DeWan, John Davis

Keywords

Detection, Habitat Fragmentation, Marsh Birds, Occupancy, Population decline, Wetland, Water birds, Wetland ecology

Subject Categories

Biology

Abstract

Populations of many North American marsh birds have declined over the past few decades, a trend commensurate with declines in wetland habitat area. Substantial declines in populations of breeding marsh bird species in New York State are associated with declines in wetland habitat area due to urbanization. The objective of this study was to examine what habitat and landscape features increase the probability of occupancy for nine target marsh bird species in New York State. This research was conducted in the Hudson River Valley region of Eastern New York, a region which is characterized by varied topography and geology, a diverse number of wetland habitat types, and which supports a rich fauna and flora. This region has also undergone high levels of natural habitat loss, fragmentation, and degradation, due to encroachment by residential and commercial development. I evaluated marsh bird occupancy by conducting call-broadcast surveys at 173 randomly selected wetland points. Target species included six secretive birds, which rarely vocalize and are hard to detect: American Bittern (Botaurus lentiginosus), Least Bittern (Ixobrychus exilis), King Rail (Rallus elegans), Pied-Billed Grebe (Podilymbus podiceps), Sora (Porzana carolina), and Virginia Rail (Rallus limicola). Due to the secretive nature of these species, existing monitoring programs have not adequately determined distributions of these marsh birds. Newly standardized methods at the national level have addressed the secretive nature of these birds. Three other target species were also evaluated, including Alder Flycatcher (Empidonax alnorum), Marsh Wren (Cistothorus palustris), and Swamp Sparrow (Melospiza Georgiana). By implementing a standardized broadcast surveying method, marsh bird presence and absence can be more accurately determined. Surveys were conducted during the breeding season in New York, between the end of May and beginning of July of 2009. Two of the seven secretive marsh bird species were detected, as well as all three other target species, over the course of the study period. Habitat components that were evaluated included urban density, represented here as the percentage of four urban land use categories (open space, low density, medium density, and high density development) within a 3.14 km2 buffer zone of each wetland, proximity to roads, wetland area, and vegetation cover type. Occupancy modeling was used to determine relationships between probability of detection and both survey methods and habitat features. Survey-specific variables correlated with detection varied with species, but occupancy model results suggest that wetland area was strongly correlated with 3 species; Virginia Rail, Alder Flycatcher, and Swamp Sparrow. Vegetation cover type was positively associated with occupancy for Virginia Rails, while urban density was negatively associated. Proximity to roads was negatively correlated with occupancy of Alder Flycatcher, while increasing wetland size was the only variable positively associated with Swamp Sparrow occupancy. Urbanization has been implicated as a primary factor in the reduction of mean wetland size, increase in wetland isolation, and degradation through pollution and other disturbances. However, variables associated with urbanization were not significant predictors of occupancy for this study. My results do suggest that larger wetlands are more attractive for a variety breeding marsh bird species. Wetland obligates, such as Virginia Rails, also chose nesting habitat based the spatial arrangement of emergent vegetation and open water. Conserving marsh birds amid urbanization may require more attention to protection of large, complex marsh habitats. However, given that this study was only conducted over one breeding season, longer term studies may be needed to better understand the relationship between urban factors and marsh bird declines in the Hudson Valley.

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