There are many of us who have felt the tedious effects of traveling the same path, to the same destination, every day. We are not alone. Many species of wading birds make a similar commute to and from home each day, only they have been doing it for thousands of years. Herons, egrets, wood storks, roseate spoonbills and white ibises migrate daily between the plentiful feeding grounds of the south Florida mainland and the protective nesting canopy of the Florida Bay mangrove islands.
Most of the wading birds nest in large colonies, typically in trees on mangrove islands in Florida Bay. These social aggregations are called rookeries and usually contain a mixture of species, with great egrets perhaps nesting close to tri-colored herons and white ibises.
Each morning many of the birds fly great distances from their rookery to foraging locations in the Everglades where the freshwater marshes provide a smorgasbord of food.
Wood storks, unusually adept at soaring on rising air currents, often commute as far as 35 miles whereas most ibises travel less than six miles. The majority of great egrets journey less than five miles, however small numbers do fly more than 15 miles and occasionally as far as 25 miles.
Within the Everglades there are thousands of acres of water less than a foot deep and filled with small fish, crabs, and shrimp ö all of them easy to catch and ready to eat.
The birds make the long return flight each evening to avoid being preyed upon by the many mammals and reptiles found in the Everglades.
During the dry season, December through May, the retreating water line in the marshes traps and concentrates many aquatic organisms and provides excellent feeding conditions for the flocks of waders. By late in the dry season, usually March to April, Everglades National Park scientists have recorded densities as high as 600 fish per square meter in the deeper, central marshes.
As the marshes dry and the food supplies become increasingly abundant, the wading birds form their nesting colonies. For the larger, long-ranging species like common egrets and wood storks, colonies may form as early as December or January. The smaller waders with shorter foraging ranges wait until March to nest, at sites close to the better feeding areas. All species must complete nesting before the next cycle of summer rains, usually beginning in June.
While this annual cycle appears simple, many subtle differences between years--the amount of marshland that is reflooded by summer rains and water deliveries to the Everglades, and the timing and rate of winter/spring dryingöhave major influences on both the food resource and the timing, location, and size of wading bird colonies.
Water management projects have severely disrupted the natural relationships between wading birds and water conditions. As a result, sharply reduced nesting success has led to a reduction in the number of wading birds, from a maximum of 300,000 birds in the 1930s, to 15,000-20,000 by the early 1990s.
Current restoration efforts focusing on trying to mimic the natural cycles of the Everglades/Florida Bay system will help to improve the nesting success of the wading birds.
For more information on this research, contact the Florida Bay Education Project at 305-852-3592. Additional information on a variety of topics is available from the University of Florida/Monroe County Cooperative Extension Service, 5100 College Road, Stock Island or call at 292-4501; fax: 292-4415; email: firstname.lastname@example.org or visit our web site http://monroe.ifas.ufl.edu. Our services are free and available to all without regard to race, color, sex, or national origin.