Wood Storks (Mycteria americana) in the southeastern United States decreased from 10,000 breeding pairs in 1960 to 2,500-5,000 pairs in the late 1970s. The number of breeding pairs appeared to increase to S,OOO-6,000 by the mid-l 980s. Since the mid-1970s the center of breeding in the southeastern United States has shifted north. Fewer birds have nested in the traditional southern Florida colonies, while the number of pairs nesting in northern Florida, Georgia, and South Carolina has been increasing annually. Storks nesting in the northern colonies appear to be reproductively more successful than those in the south, which may explain the increase in total numbers.

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We analyzed 30 years of Christmas Bird Count (CBC) data for Florida populations of six species of wading birds: Great, Cattle, and Snowy Egrets; Little Blue and Tricolored Herons; and the Wood Stork, a federally listed endangered species. These species are conspicuous components of wetland ecosystems, and the target of numerous management efforts in the state and region. The nonlinear dynamics of these populations were assessed through time series of birds seen during volunteer-based surveys and the first differences of successive annual counts, autocorrelations, and two new metrics: correlation time and a momentum oscillator. CBCs have the advantage of being conducted regularly over a large geographic scale. When properly analyzed, CBCs are among the few available sources of reliable population information for small, dark-plumaged species such as Little Blue and Tricolored Herons. Population trends assessed for all species by CBCs paralleled the known or suspected trends determined by breeding-season aerial and ground surveys, conducted by professional biologists. Cattle Egret populations have declined following rapid expansion through the 1960s and 1970s; Snowy Egret and, to a lesser extent, Tricolored Heron populations have declined throughout the study period; Little Blue Heron and Great Egret numbers have been relatively stable. Wood Storks, following a period of decline that lasted into the mid-1970s, slowly recovered through the 1980s. Only Cattle Egrets displayed strongly deterministic population dynamics, indicating that predictions of population trends for the other species will require stochastic models with broad confidence bands.

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