What can birds tell us about watershed health?

Because of their dependence on different habitats, birds can be good indicators of some changes to watersheds. For example:

• The fish-eating Osprey is sensitive to pollutants that bioaccumulate in fish. In the 1960s, Osprey had declined greatly due to the effects of DDT. Since EPA banned the use of DDT, Osprey numbers have increased significantly.

• Swainson's Hawk numbers have declined due to the loss of the riparian forests in which they nest. In California, for example, approximately 95% of the original riparian forest has been lost to agriculture, urbanization, flood control, and dams. This species is an indicator of the presence of healthy riparian forest, which in watersheds, has many other important benefits, including water filtration, water retention, stream shading for fish, and providing food for aquatic insects that fish and birds eat.

• A number of warbler and thrush species are declining due to the fragmentation of the forest habitat in which they nest. Fragmentation not only reduces useful habitat, but it allows predators, such as domestic cats, easier access to vulnerable nests.

• Many grassland species, such as Henslow's Sparrow and Meadowlarks in the east and Burrowing Owls and Loggerhead Shrikes in the west, are declining due to the conversion of grasslands to agriculture and urban uses. Pesticide use may also be a factor in the decline of some of these species.

• Hundreds of thousands of migratory birds are killed each year when they collide with towers and buildings during their migration at night. Some species are severely affected, such as the rare Tennessee Warbler, a bird commonly killed by towers.