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Intra- and Inter Marsh Variability in Habitat Use by Wading Birds
Project 1: Use of Urban Marine Habitats by Foraging Wading Birds
Salt marshes perform many functions that are of value to surrounding ecosystems and to humans, including flood control, water quality maintenance, and the provision of habitat for fish, shellfish and wildlife. These wetlands are considered essential to the ecology of estuarine wildlife in that they provide structure and life support functions to critical life stages and aid in the protection and development of many species. However, they are rapidly being lost or destroyed by land-use activities, and alteration of these habitats has been identified as a major cause of endangerment for species within the United States. In light of this, there is a need for research that quantifies the structure and life support functions of specific habitats and habitat complexes for fish and wildlife to aid in the study of the biological effects of both incremental and catastrophic habitat alteration.
For this project researchers at the US EPA Atlantic Ecology Division and the Narragansett Bay National Estuarine Research Reserve examined the effects of human disturbance, available foraging habitat, and prey abundance on wading bird density and species richness at 17 urban coastal sites in Greenwich Bay, an 11.7 km2 sub-estuary of Narragansett Bay, RI. Wading bird density (0.62 ± 0.12 birds ha-1) and species richness (average 4.49 ± 0.37 species across all sites) were not influenced by passive human disturbance (i.e., extent of urban land surrounding a site). However, wading bird density and species richness both decreased significantly as active disturbance (i.e., number of boats moored or docked upstream of the site) increased (r = -0.56, F = 6.85, p = 0.019 and r = -0.73, F = 16.6, p = 0.001, respectively). In addition, both density (r = 0.72, F = 16.2, p = 0.001) and species richness (r = 0.72, F = 16.2, p = 0.001) increased concomitantly with a prey index that combines the density of fish and invertebrates on which the birds feed density with the amount of available shallow water foraging habitat at a site. Our results suggest that wading birds i) may not be negatively affected by urban land surrounding estuarine foraging areas in and of itself; and ii) may be utilizing urban areas in the absence of high levels of active disturbance to take advantage of potentially enhanced prey resources. In the case where the benefits of foraging at a site outweigh the costs related to human disturbance, urban marine habitats may need to be considered for restoration or protection from further increases in active human disturbance.
Results are summarized in McKinney, R.A., K.B. Raposa, and T.E. Kutcher. Use of urban marine habitats by foraging wading birds. Urban Ecosystems in review.
Project 2: Energetic Requirements of Coastal Birds Foraging in Urban Marine Habitats
Coastal birds use salt marshes in Narragansett Bay for foraging, even in highly urban areas where they are subject to pollution and human disturbance. Ecologists from the Narragansett Bay National Estuarine Research Reserve and the US EPA are teaming up to study the impacts of human disturbance on heron and egret populations foraging in urban salt marshes during migration. We are studying their behaviors and developing energetic models to track the impacts of human disturbance on population fitness.
For more information contact Rick McKinney (mckinney.rick@epa.gov) or Kenny Raposa (kenny@nbnerr.org).
