Wading Bird Response (No. and Central Everglades)

    Project Status     

Mandate: Comprehensive Everglades Restoration Plan

Management Issue:

Wading birds played a key role in the initial attempts to preserve the Everglades, and they are now playing a central role in the Comprehensive Everglades Restoration Plan (CERP) to restore the Everglades. In the early 1900s, declining wading bird populations served as a rallying call to the public to save the Everglades. The mental image of "clouds of wading birds darkening the sky as they pour out a roost" gave people a visceral connection to one of the country's last truly wild places. Early conservationists used that reaction by the public to argue successfully that it was a sight worth conserving for future generations.  
Today, scientists are no less in awe of these magnificent birds but scientists also recognize that their place in the ecosystem can shed light on how it functions and provide direction for how it can be restored. In other words, they are good "indicator species." Wading birds are able to track food densities and water levels across large areas of the Everglades, because they fly long distances and are quick to visit places where other birds are feeding. Wading birds exemplify the critical connection between Everglades animals and water. In the years ahead, CERP will rely on that connection with water and will use wading birds as a tool to guide the Everglades restoration effort.

Research Project Overview:

The animations on this web site depict wading birds in the central Everglades observed during aerial surveys from 1985 to 1994. The surveys were part of a study funded by the South Florida Water Management District and conducted by the National Audubon Society (Bancroft et al. 1995).  The study has continued and since 1995, has been funded and conducted by the U.S. Army Corps of Engineers. A summary of recent data appears annually in the South Florida Wading Bird Report.

Each month from January through June (surveys were often flown in August and December as well), researchers recorded the number of wading birds of each species they observed in 2x2 km grid cells that comprised the Water Conservation Areas (WCAs) (Bancroft et al. 1995). They also classified the amount of surface water in each cell as dry (no surface water except for alligator holes, canals, and ponds), transitional (some surface water present), or wet (water completely covering the ground). In wet years, most cells were wet most of the time and the covering of surface water did not reflect relative water depths among cells. Therefore, for wet and flooded years, the District used simulated water depths from the South Florida Water Management Model.

For these animations, the District used data from surveys conducted in 1986-1990 and 1993-1994 and excluded cells that bordered on canals. Each year was classified statistically as a flood year, wet year, or a drought year. We combined data on bird abundance, surface water, and water depths in a geographical information system (GIS). For each of five wading bird species (Great Egret, Great Blue Heron, White Ibis, Glossy Ibis, Wood Stork), the District created monthly distribution maps and then animated them so that over the course of a wet and dry cycle, the simultaneous movement of water and birds could be viewed. The animations are classified by bird species and water condition year (dry, wet, or flood).

Application of Results:

Despite the sophisticated analytical tools available to scientists, one of the most powerful ways to document the response of wading birds to water patterns is to simply observe them. Watch the animation, as birds move across the landscape in response to the recession of water in the dry season (typically December to May). Many leave the Everglades after the onset of the rainy season (typically June to November). You can also compare how the different species move across the landscape in flood years versus drought years. Notice in the animations, not only the movement of birds, but also how the abundance changes. In flood years, such as 1994, the birds tend to be dispersed in low densities across the landscape, and in drought years like 1990, birds are highly concentrated at the drying edge. Birds leave the Everglades temporarily when the surface water disappears, just as they do when the rainy season begins. With the help of statistical tools, scientists are beginning to identify specific characteristics of these movement patterns that are linked to years of good nesting. CERP will use this information to refine hydrologic targets and to ensure that recovery efforts of the Everglades ecosystem continue to move toward them.