RESPONSES OF MARSH FISHES AND BREEDING WADING BIRDS TO LOW-TEMPERATURES - A POSSIBLE BEHAVIORAL LINK BETWEEN PREDATOR AND PREY

In the Everglades of southern Florida, several species of spring- and winter-nesting wading birds (Ciconiiformes) often abandon their nests in response to periods of cold or wet and windy weather. Using stepwise logistic regression of a variety of hydrologic and meteorologic variables on the probability of great egret nest failure, we found that cold temperatures and high wind speeds were most closely associated with nest failure in the Everglades. Water level fluctuation was not a significant correlate of failure. Quantitative visual surveys in the field showed that even moderate cooling events (15-degrees-C minimum daily temperature) dramatically altered the observed densities of marsh fishes. In controlled conditions in the laboratory, we observed centrarchid, poeciliid, and cyprinodontid fishes during normal high (19-23-degrees-C) and simulated cold snap (8-11-degrees-C) temperatures. At low temperatures, the fishes exhibited reduced activity, sought refuge by hiding in vegetation and/or substrate, and fled our approach to the tank at much greater distances. Threshold temperatures for these behaviors varied considerably between the laboratory (9-11-degrees-C) and field (15-20-degrees-C), and may be explained by differences in the previous thermal experience of the two groups of fishes. We hypothesize that the temperature-induced scarcity of fishes during spring cold snaps is an important cause of disruption of nesting for several species of wading birds in the Everglades.