There is no denying the beauty of birds flying across a clear blue sky, or the splendor of the sounds of the songbirds, or the magnificent power of a raptor as it dives at prey. Migratory birds add color and music to the spring. These are all pleasures that even the most casual observer can enjoy. But millions of Americans consider themselves to be birders, people who spend time in the field identifying birds. These "birdwatchers" spend many hours viewing birds and gathering data which can help scientists track the locations and numbers of different species during migration. For every birder there is equipment to buy, from binoculars to field guides to tents. Likewise, millions of dollars is fed into the bird "hotspot" communities, such as Cape May, New Jersey. These communities thrive on impressive sums of tourist dollars as avid birders return each migratory season hoping to catch a glimpse of a flock taking off for the day or to sight a rare bird.

But aside from the aesthetic and economic values of birds, what other roles do birds play in our ecosystems? Birds can be used as environmental indicators to assess the health of an environment. Every year migratory birds may return to the same breeding territories. Evidence of a declining bird population in a particular region may indicate another problem present in the habitat, perhaps the disappearance of their food source or preferred nesting sites.

The decline of the Kentucky Warbler in certain regions can be attributed to the overpopulation of white-tailed deer. Excessive numbers of browsing deer can devastate the plant life that would normally provide cover for the warbler nests.

Birds are natural enemies of many insects. If birds are removed from a local food chain, certain insects will reproduce out-of-control, and a normally harmless insect species may become an annoying pest. In turn, as the immense insect population feeds, local plant life will suffer. When such things happen, ecosystems become subject to a sort of "domino effect": the crucial balance is lost.

Despite the significant role birds play in local ecosystems, every year the numbers of migratory birds that return to our region decreases. Migrating birds are amazingly tough on their long journeys. They can usually survive bad storms, high winds and threats from a variety of predators. But believe it or not, humans are their biggest threat. How can this be?

Because people have changed the natural landscape in so many ways, we present birds with new challenges every day. Suburban sprawl, rain forest fragmentation, deforestation, and commercial development all contribute to the difficulties of finding food, nest sites and raising young.

Forests in which birds nest, feed, and find shelter have been cut down or fragmented. Many wetlands, equally important to other species, have been filled in or drained. The key coastal zones that are used as stopover points are being developed for resorts and vacation homes.

Pesticides are another problem, not only because they are applied to fields, golf courses and suburban lawns where birds may land, but also because they are used in forests to eliminate caterpillars and other insects that birds rely on for food. The issue of pesticide use is complex, for chemicals can have many direct and indirect effects that are only now beginning to be understood.

There are other things humans do that directly affect the survival of migrating birds. Millions of birds fly into glass and mirrored windows every year. Cats that people keep as pets and let outdoors kill millions more. Man-made structures like radio and television towers and tall buildings-which are lit up at night when migrating birds travel-attract birds and cause confusion or collisions.

Click on "How You Can Help" to discover the many ways you and your community can make the world a little less hazardous for these amazing migrants.

Other useful bird migration sites:
United States Geological Survey: Migration of Birds
http://www.npwrc.usgs.gov/resource/othrdata
/migratio/migratio.htm#table

Hawk Mountain Sanctuary
http://www.hawkmountain.org/

Smithsonian Migratory Bird Center
http://www.si.edu/smbc/fxshts.htm