The value of wading bird habitat in urbanized wetlands
Birds
A snowy egret. Image credit, Jack Wolf.Is it really possible that some wading birds prefer urbanized wetlands to their natural habitat? Researchers have found that the extent of developed land arround a salt marsh may improve wading bird density. But the reason may be bad for conservation.
The study authors suspect that urbanized areas may support less mammalian and avian predators and may contain more non-point source human waste inputs into the water thereby enhancing prey abundance. The study also found that active habitat disturbances such as increased boating traffic negatively impacts wading bird density and species richness that can override benefits from surrounding development.
Studying the effects of urban disturbance on wading bird habitat...
Wading birds, shorebirds, and waterfowl seek prey within the shallow waters of tidal wetlands. Even though coastal areas are often highly developed and popular for recreation, little is known of direct and indirect impacts that these disturbance can have on water birds. In 2004, Ashley Traut and Mark Hostetler demonstrated that Florida wading birds preferred habitat surrounded by developed land, but the study did not take into consideration habitat characteristics.
The current study by Richard McKinney, Kenneth Raposa, and Thomas Kutcher examined the effects of both active and passive human disturbances on wading birds, while also looking at prey abundance and availability of foraging habitat. They observed 17 salt marshes in Greenwich Bay - surrounded by the city of Warwick, Rhode Island. The city contains dense residential neighborhoods along with transportation infrastructure, commercial centers, marinas, shipyards, and other amenities for the 85,000 residents.
The researchers sampled each marsh for birds and prey and counted boats biweekly for 2 years. In order to incorporate availability of foraging area, the researchers divided the prey count by the acreage of shallow water (<15 cm). They used boat counts as an indicator for active human disturbance and recorded the proportion of urban land within a 30.5 m buffer to signify passive disturbance.
The surveys found that wading bird populations were mostly comprised of snowy and great egrets (Egretta thula and Aldea alba). The wading bird densities increased with prey abundance as well as passive disturbance, i.e. more urban land surrounding the site. However, the direct human disturbance from recreational boating negatively impacted bird density and species richness.
The study shows that urbanized tidal wetlands can provide valuable habitat to some wading birds and should be given closer attention for preservation and restoration. However the study authors caution:
"It is important to consider that despite their apparent suitability for foraging wading birds, urban coastal habitats that are structurally degraded (i.e., those that exhibit detrimental changes in vegetation patterns, hydrology, or area) may be of little value to species that traditionally used these areas for breeding (e.g., seaside sparrow Ammodramus maritimus, willet Catoptrophorus semipalmatus). In addition, utilizing these resources may come at a cost: the fitness of birds that utilize urban foraging habitats may be impacted both by the increased levels of human disturbance and exposure to higher levels of human-derived pollution, including persistent organic contaminants and trace metals."
--Reviewed by Evyan Borgnis
| Source: | Urban Ecosystems |
| Title: | Use of marine habitats by foraging wading birds |
| Authors: | a) Richard McKinney, b) Kenneth Raposa, and c) Thomas Kutcher |
|
a) U.S. Environmental Protection Agency, Narragansett, Rhode Island |
Reader Comments