The impact of soil contamination on birds.
The development of open space in and around major population centers has continued unabated for decades. Within the last decade, urban sprawl has increased by more than fifty percent across the United States. Unfortunately, such rapid land-use change has caused many bird populations to decline or even disappear.
Although many migratory and resident bird species have already been extirpated in urban and suburban habitats, some do persist. For the species that remain in these heavily disturbed and common habitats, we know surprisingly little about the factors that may limit or regulate population levels.
One group of factors that may be detrimental to all organisms within urban ecosystems is metal contaminants, such as lead, zinc, copper, cadmium, mercury, nickel, and iron, that get deposited in soil.
Metal contaminants are introduced into food webs at the bottom of the food chain and reach earthworms and other invertebrates that live in the soil. When consumed by organisms such as birds and snakes, the contaminants and their potential toxic effects accumulate within sensitive organs and tissues.
Understanding how a range of metals influence the health and functioning of organisms is essential to predicting how continued urbanization and its associated affects will impact wildlife populations across the United States.
There are four primary sources of heavy metals in residential areas:
Before 1986, vehicle exhaust from automobiles contributed lead from leaded gasoline. Dust from tires and brake linings contributes iron, copper and zinc to residential soils.
Lead-based paint from homes contributes to soil contamination.
Other contaminant sources are from commercial fertilizers applied to home gardens and lawns. Commercial fertilizers all contain high levels of cadmium, copper, zinc, and nickel.
Finally, at the regional level, atmospheric deposition distributes heavy-metal pollutants such as mercury from an urban core to outlying rural areas.
Eight common nesting birds found within the urban land-use gradient of the Washington, D.C., region will be studied: American robin, gray catbird, song sparrow, northern cardinal, northern mockingbird, house wren, Carolina wren, Carolina chickadee.