Distribution and Abundance of Wading Birds in the Big Cypress National Reserve

Nelson, David; Theriot, Craig

Major changes in water management that are currently being proposed or implemented will alter the hydrology of the Big Cypress National Preserve and, consequently, the use of these areas by wading birds. Because these areas support huge concentrations of foraging wading birds (Hoffman et al. 1994) and the largest percentage of the remaining nesting wading birds in the Everglades (Ogden 1994), monthly systematic reconnaissance flights (SRF) were conducted to investigate and monitor the relationship between modified hydrologic patterns in the Everglades system and the distribution and abundance of these wading birds. Surveys were flown with a fixed winged aircraft at an altitude of 60 meters along 29 parallel transects with 2 km spacing in the Big Cypress National Preserve. Wading birds were enumerated, their positions recorded, entered into a database, and summarized into tables. Densities of each species were separated into 4 km2 cells and plotted onto maps of the study area. The monthly percent of wet cells for the 2000 survey months declined from 72 % wet cells in January to 10% in May and 18% in June. The percent of wet cells in April increased in April to 31% with a major rain event during this month. The general pattern of decreasing wet cells from winter to late spring in 2000 was similar to the 1999 pattern for the Big Cypress National Preserve. The population estimates for wading birds during 2000 followed the same pattern as 1999 declining from highs in January and February to lows in May and June. Wading bird average monthly relative abundance was 8.7% lower in 2000 (18,774) than in 1999 (20,412). Great Blue Herons, Great Egrets, small dark herons and Glossy Ibises had higher average monthly relative abundance in 2000 than in 1999. While small white herons, White Ibises, Wood Storks and Cattle Egrets had lower average monthly relative abundance in 2000 than in 1999. The areas with greatest densities of wading birds in Big Cypress National Preserve were the southeast comer, the southwest comer, and east-central (L-28 Gap area). These areas tended to remain wet. In addition, large flocks of roosting birds were observed in the northern five or six transects. The average monthly density of wading birds in Big Cypress National Preserve for 2000 (5.83 birds/km2) was lower than average monthly densities for WCA 1 (26.17 birds/km2), WCA 2A (11.47 birds/km2) and WCA 3A (18.69 birds/km2) but higher than WCA 3B(5.43 birds/km2) and WCA 2A(l.80 birds/km2). Extensive areas of dry habitat in central Big Cypress were not used by wading birds. However, the cypress trees in northern big Cypress National Preserve are used by large numbers of wading birds for roosting particularly prior to the breeding season.