Salt Marsh Bird Community Responses to Open Marsh Water Management

Graduate Research Assistant: Marnie Pepper (Graduated Spring 2008)

Collaborators: Jacob Bowman and Hal Laskowski

Salt marshes are highly productive ecosystems that provide critical breeding and foraging habitat for many bird species. Open marsh water management (OMWM), a method of mosquito abatement through habitat alteration, is a widely practiced management technique in Delaware and New Jersey salt marshes. Although OMWM may alleviate the need for pesticide applications, the effect of these habitat modifications on obligate salt marsh birds is not fully understood and remains an information priority for the United States Fish & Wildlife Service National Wildlife Refuge System. The objectives of the research were to develop a method to quantify OMWM, to use an index of marsh bird community integrity along with measures of avian species richness and abundance to evaluate the effect of OMWM on marsh integrity, and to determine the impacts of OMWM on Seaside Sparrow reproductive success and ecology. We found that the relative abundance of the salt marsh obligate species was more than 1.5 times greater on limited OMWM sites than extensive sites (P ≤ 0.05). Relative abundance of Seaside Sparrows was 2 times greater on limited OMWM than on extensive OMWM (P ≤ 0.05). Seaside Sparrow territory density and nesting density was also 2.5 times greater on limited OMWM plots than extensive OMWM plots (P ≤ 0.05). OMWM did not appear to benefit most marsh bird species or guilds, but may negatively impact populations of salt marsh obligate species and Seaside Sparrows. OMWM may be used as an alternative means of mosquito control, but should not be considered a method of habitat enhancement for obligate salt marsh bird species.

Mercury Contamination in Tidal Marsh Birds of Delaware Bay

Graduate Research Assistant: Sarah Warner

Collaborators: Jacob Bowman and Russ Greenberg

North America encompasses the greatest concentration of tidal marshes. Fifteen endemic species are found in these marshes, the most of any coastal region in the world. These sensitive estuarine habitats are exposed to daily inundation of tides, making the flora and fauna that dominate the areas specialized to this fluctuating environment. The unique environmental gradients associated with tidal marshes and the relatively simple avian community make them a model ecological system for study. A significant factor to salt marsh degradation is heavy metal and chemical contamination. Mercury (Hg) is a known pollutant and in the Unites States major sources come from point sources such as coal-fired plants, industrial boilers, incinerators and chlorine manufacturing plants, and non-point sources such as atmospheric deposition. Approximately 6600 metric tons enter the atmosphere annually, with 33% - 36% directly emitted from anthropogenic sources. Research on Hg toxicity in coastal marsh ecosystems is limited. Presently, there is no information on Hg contamination tidal marsh sparrows in Delaware Bay. The goal of this project is to estimate Hg in Delaware salt marshes using tidal marsh sparrows as a biological indicator.

Monitoring Breeding Bird Communities to Assess Forest Condition in Mid-Atlantic National Parks

Graduate Research Assistant: Sarah Goodwin

Collaborators: Jacob Bowman, Shawn Carter, and Chris Williams

Measuring the complex interactions of anthropogenic stressors on natural systems is a difficult but increasingly important task. Development and conservation are historically at odds with each other, and with continued growth will come increased strain on natural systems. In the Mid-Atlantic, in particular, human development is continuing at a rapid pace. It has been estimated that between 1976 and 1996, development around Washington DC increased by 22 km2 per year. In the National Capital Region (NCRN) of eleven National Parks (MD, VA, WV and D.C.), the density and/or abundance of forest breeding birds was selected as one of 21 vital signs to be monitored (NPS 2005). Of the 80 plus bird species that are known to breed in NCRN forests, many have been designated priorities for conservation effort. The overall goal for monitoring forest breeding birds is to determine the changes in density and/or relative abundance across the network of parks. This project will work to integrate the avian monitoring data into an overall condition assessment of not only the breeding bird community but also the forested ecosystems within the NCRN.

Development of Avian Rapid Assessment Metrics to Monitor Salt Marsh Integrity

Graduate Research Assistant: Whitney Wiest

Collaborators: Jacob Bowman, Hilary Neckles, Glenn Guntenspergen, and Hal Laskowski

Coastal wetlands are unique ecosystems comprising flora and fauna that have adapted and evolved to the extreme conditions of hydrology, soils, and salinity found within these areas. Numerous wildlife species are highly dependent on salt marshes as breeding, feeding, migratory, or wintering habitat. Wildlife species dependent on salt marshes are some of the highest conservation priorities in the US. Consequently, a high preponderance of National Wildlife Refuges (NWR) have been established along coastal areas to protect large tracts of salt marsh and wetland-dependent species. The NWR System (NWRS) includes 161 coastal refuges. Approximately 1,045,925 acres of coastal wetlands occur on refuges in the lower 48 states. Unfortunately, there are few coastal salt marshes that remain in pristine condition. The majority of salt marshes have experienced some form of anthropogenic alteration such as oil spills, chemical mosquito control, drainage for mosquito control, salt hay farming, introduction of invasive species, restricted tidal flow, road construction, or channelization. These alterations impact both the intrinsic value of salt marshes as well as the quality of salt marsh habitat for the unique wildlife they support. Among the most important anthropogenic changes operating at the landscape/regional scale are the threats posed by global climate change. Sea level rise is a specific consequence of global climate change, and as sea-level rise accelerates and inundates some salt marshes, migration/creation of new salt marshes will be severely hampered by human development of adjoining lands. The goal of this project is to develop avian metrics that can be used to monitor tidal marsh condition and the intrinsic habitat value to wildlife communities that depend on these habitats. USGS scientists are developing habitat-based indicators of tidal marsh condition that can be incorporated into a multi-metric index of ecosystem integrity. This project will complement USGS work by developing avian indicators of the intrinsic value of these systems to wildlife. Incorporation of avian indicators into the multi-metric index will enhance the utility of this tool for assessing the overall habitat value of tidal marshes.

The Effects of Atmospheric Deposition on a Delaware Forest Bird Community

Undergraduate Research Assistant: Kelly Schaeffer

Collaborator: Jacob Bowman

The atmospheric deposition of sulfur and nitrous oxides (acid rain) and mercury (Hg) and into forested ecosystems are environmental stressors which may contribute to the recent decline in forest bird populations in the northeast USA. Acid rain can greatly decrease the amount of calcium (Ca) available to breeding birds. Methylmercury (MeHg) is the bioactive form of mercury which is most often found in avian blood. The negative effects of MeHg on birds in aquatic systems are well documented, but only recently have investigations into its effects on terrestrial avian species been initiated. To estimate the potential effects of these stressors on a forest breeding bird community, we used the University of Delaware Ecology Woods (UDW). We sampled soil calcium and calcium-rich prey systematically throughout UDW using the Birds in Forested Landscape protocol to determine the effects of acid rain on soil chemistry and prey availability. To create an Hg exposure profile in the forest breeding birds for UDW, we sampled blood from five forest breeding bird species: American Robin (Turdus migratorius), Gray Catbird (Dumetella carolinensis), Carolina Wren (Thryothorus ludovicianus), Northern Cardinal (Cardinalis cardinalis) and Wood Thrush (Hylocichla mustelina). To determine the effects of Hg body burden on reproductive success, we used the long-term Wood Thrush demographic study to associate reproductive success with Hg exposure. This study examined the effects of atmospheric deposition of acid rain and mercury on the forest avian community in UDW. We found startlingly low levels of soil calcium and calcium rich prey which may be a limiting factor for forest birds breeding in UDW. We found baseline levels of mercury present in all seven forest bird species sampled with the Carolina Wren and Wood Thrush having the highest mean Hg concentrations. Mercury at these low levels did not have a direct negative effect on Wood Thrush reproductive success, as measured by number of successful nests and number of young fledged. These data suggest, that of the two stressors to forest ecosystems (acid rain and Hg deposition), acid rain seems to be the more likely explanatory variable in the recent decline of Wood Thrush in the UDW.