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Use of Urban Marine Habitats by Foraging Wading Birds
Citation:
MCKINNEY, R. A., K. B. Raposa, AND T. E. Kutcher. Use of Urban Marine Habitats by Foraging Wading Birds. Urban Ecosystems. Springer Science+Business Media B.V, Dordrecht, Netherlands, 13(2):191-208, (2010).
Impact/Purpose:
This study investigated the relative importance of human disturbance in the context of other landscape and biological factors that may be influencing habitat use by foraging wading birds in urban salt marshes. We found that the percent open water at a site had the highest influence on wading bird use, but that the percent urban land surrounding a site and number of boats moored upstream of a site (a surrogate for direct human disturbance from boating) also were important variables in models explaining wading bird density. In these models, wading bird density actually increased with increasing urban land around the sites. Our results suggest that while direct disturbance from boating is influencing their distribution, wading birds may preferentially utilize sites with high surrounding urban land use in the absence of boating disturbance, possibly to take advantage of enhanced prey availability. Our research suggests highly modified coastal areas of urban estuaries could provide needed resources for migrating waterbirds and should be identified and protected to the extent possible in spite of their highly disturbed settings.
Description:
Wading birds that utilize coastal habitats may be at risk from increasing urbanization near their foraging and stopover sites. However, the relative importance of human disturbance in the context of other landscape and biological factors that may be influencing their distribution is unclear. We looked at the effects of human disturbance, along with changes in available habitat and prey abundance, to evaluate the importance of these characteristics in determining wading bird distribution at a series of 17 urban coastal sites. The average density of wading birds at our sites was 0.62 ± 0.12 birds ha-1 and significantly increased with increasing percent open water < 15 cm r = 0.72, F = 16.2, p = 0.001). However, wading bird density decreased as the log of the number of boats moored or docked upstream of the site increased (r = -0.56, F = 6.85, p = 0.019). Wading bird species richness (average 4.49 ± 0.37 species across all sites) also increased with increasing percent open water (r = 0.63, F = 9.75, p = 0.007), and decreased with increasing number of boats (r = -0.73, F = 16.6, p = 0.001). When we evaluated sets of habitat characteristics using information-theoretic (Akaike Information Criteria) modeling, percent open water had the highest cumulative relative importance, followed by the percent urban land surrounding a site and number of boats, in models explaining wading bird density at the sites. In these models, wading bird density actually increased with increasing urban land around the sites. Our results suggest that while direct disturbance from boating is influencing their distribution, wading birds may preferentially utilize sites with high surrounding urban land use in the absence of boating disturbance, possibly to take advantage of enhanced prey availability. Highly modified coastal areas of urban estuaries could provide needed resources for migrating waterbirds and should be identified and protected to the extent possible in spite of their highly disturbed settings.
