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

Nelson, David; Metzger, Robert

This report covers a study done to test the effect of changing hydrology in Big Cypress National Preserve on wading birds. Major changes in water management that are currently being proposed or implemented that will alter the hydrology of the Everglades/South Florida Ecosytem 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. In Big Cypress National Preserve the monthly percent of wet cells declined from 48% wet cells in February 2002 to 6% in April 2002 then increased in June 2002 to 100 %. 2001 was generally dry from January (18% wet cells) to June (14% wet cells). In 2000, the percent of wet cells decreased from 72% in January 2000 to 13% in March 2000. Water levels were higher in 2002 than 2001. In 2002, water levels declined from October/November 2001 until June 2002. In June 2002 water levels begin to increase with the influx ofrain. In 2001, water levels followed the same pattern as surface water declining to April2001. Water levels were lower from January to April in 2001 than the same months in 2000. The population estimates for wading birds while higher in 2002 than 2001 followed a similar pattern as 1999, 2000 and 2001 declining from highs in January/February to lows in May/June (Appendix J)(Nelson and Theriot, 2000). ). Wading bird average monthly relative abundance was much higher in 2002 (14,325) than in 2001 (9,189). Wading bird average monthly relative abundance was much lower in 2001 (9,189) than in 2000 (18,774) and 1999 (20,412). Great Blue Herons had average monthly relative abundance in 2002 lower in value than as 2001. While Great Egrets, White Ibises, Glossy Ibises, Wood Storks, Cattle Egrets, small dark herons and small white herons had higher average monthly relative abundance in 2002 than in 2001. Great Egret average monthly relative abundance in 2002 was over twice the average in 2001. The areas with greatest densities of wading birds in Big Cypress National Preserve were the southeast comer, the southwest comer, and east-central (L28 Gap area). These areas tended to remain wet longer than other areas. The average monthly density of wading birds in Big Cypress National Preserve for 2002 (4.45 birds/km2) was lower than average monthly densities for WCA 1 (20.58 birds/km2), WCA 2A (26.70 birds/km2), WCA 2B (28.41 birds/km2), WCA 3A (15.52 birds/km2) and WCA 3B (5.51 birds/km2) (Nelson and Metzger, 2002). Extensive areas of dry habitat in central and northern Big Cypress were not used by wading birds.