Wading bird nesting effort as an index to wetland ecosystem integrity

Abstract

A comprehensive wading bird nesting database for the Everglades watershed in south Florida was compiled for the time period of 1903 through 2001. The limitations and applications of this database were assessed with the purpose of ultimately strengthening wading bird performance measures used as an index of ecosystem integrity for the Everglades restoration effort. The database is limited for some inferences, such as comparing between individual years, because of a lack of standardization in sampling methodology. As such, it should be used as an index of wading bird numbers rather than as an absolute population measure. However, the database is adequate to understand long-term, system-wide trends and the range of variability in nesting effort by the wading birds. Results from the analyses indicate that trends in numbers of nesting wading birds differ among species. It is estimated that the number of White Ibis (Eudocimus albus) and Wood Stork (Mycteria americana) nests have decreased by 87% and 78%, respectively, in the Everglades since the 1930s. There has also been a significant increase in the time interval between large nesting events for White Ibis and Wood Stork and a decrease in the magnitude of large nesting events for White Ibis over the past 70 years. The number of Great Egret (Ardea alba) nests has increased, the magnitude of large nesting events has increased, and the interval between large nesting events has decreased. There has also been a 61% decrease in the percentage of wading bird nests located in the southern Everglades and a 46% increase in the percentage of nests located in the central northern Everglades since the 1980s. These types of quantitative comparisons can be used to refine and strengthen the proposed wading bird performance measures used to gauge the health of the Everglades for the Everglades restoration effort. The time interval between large nesting events may be appropriate as an additional performance measure because it may capture the variable nature of wading bird numbers in response to hydrologic fluctuations in the Everglades. Received 30 November 2002, accepted 12 May 2003.