Wading Birds in South Florida

Wading Birds in South Florida

Categories: Special Report: Florida Bay

By: Dr. Ruscena Wiederholt & Dr. Stephen Davis

Photos © Brian Call

Wading birds are iconic species and top predators that reflect the health of the Everglades ecosystem. Species include roseate spoonbills, great egrets, white ibises, tricolored herons, wood storks, great and little blue herons, and snowy egrets.

Wading bird reproduction is limited by abundance of prey and their ease of capture. Prey fish and crayfish need sustainable habitat and the proper hydrological conditions to flourish. During the dry season, when wading birds are breeding, ideally fish and crayfish become more concentrated and easier for wading birds to capture (Figure 1). For this to happen, water levels need to recede at a proper rate without rising again (reversals) so that these sources of wading bird food can concentrate in sloughs (i.e., the deeper areas of the Everglades). During the wet season, when water levels rise, these prey items disperse into shallower sawgrass marshes to reproduce and avoid being eaten.

Unfortunately, wading bird reproduction has declined dramatically in the last few decades. Numbers of nesting pairs have decreased by up to 90% since the 1930s and 1940s. In addition to these declines, changes in hydrology over the last century have negatively impacted wading birds in South Florida in two fundamental ways. First, their breeding grounds have shifted inland from the historic area in the coastal Everglades. Second, the start of their breeding season is often delayed, leading to a reduced window of opportunity to produce successful nestlings. This is problematic because chicks need sufficient time (and food) to fledge before the onset of the subsequent rainy season, when the availability of prey declines.

In response to these declines, a number of restoration targets for wading birds have been established. A major focus is on increasing the overall numbers of nesting pairs. Earlier breeding seasons are another critical target, along with shifting the nesting grounds back to the historic coastal regions as well as Big Cypress National Preserve and Corkscrew Swamp.

Last year, during the 2017 nesting season, wading bird populations showed both positive and negative signs. Counting all wading birds, there was a higher number of nests than average. Great egrets and white ibises had a slightly above average nesting seasons. Wood storks, on the other hand, had the best nesting season since 2009, with almost double the 10-year average number of nests. However, tricolored heron and snowy egrets have shown sustained declines, and their nesting was well below average last year. Also, roseate spoonbills, which historically nested in Florida Bay, continue to nest farther inland.

So far, 2018 appears to be a good year for wading birds. Although official reports are not yet out, there are extremely large nesting colonies of white ibises in the central Everglades and Everglades National Park. Also, wood storks have initiated nesting earlier in the last two years.

Figure 1. The top panels illustrate the natural progression of the dry season, showing water level recession and prey concentration (in blowup bubble) leading to successful nesting. The bottom panels illustrate degraded conditions of ‘too deep’ or ‘too dry’ as the season progresses resulting in reduced food availability and failed nesting.