HEAVY-METAL CONCENTRATIONS IN GREAT BLUE HERON FECAL CASTINGS IN WASHINGTON-STATE - A TECHNIQUE FOR MONITORING REGIONAL AND GLOBAL TRENDS IN ENVIRONMENTAL CONTAMINANTS

Growing concern over the health of the world's environment necessitate s development of methods to monitor environmental changes over time. V arious proposals involving ''literally'' thousands of useful ecologica l indicators (Cairns and McCormick 1992) have been published over the past two or three decades. Hinds (1984) and Cairns and McCormick (1992 ) discuss several aspects of such proposals, including the theoretical foundations for the use of indicators in ecosystem-based monitoring. Sampling of animals often requires a choice between killing individual s in the field to allow measurement, or using an indirect or correlati on-based non-destructive sampling technique. The latter is preferred u sually for long-term monitoring programs. Sampling of feathers to dete rmine metal concentrations in tropical Pacific Rim birds, including he rons, was reported by Burger (1993), Burger and Gochfeld (1991, 1993), and Burger et al. (1992, 1993). While collection of feathers did not harm the birds, the feathers still had to be plucked from the birds. W e report a method that does not involve disturbing the birds. Great bl ue herons (Ardea herodius) feed at the top of a diverse but reasonably well understood food web. The birds are colonial during their reprodu ctive season, and gather into identifiable, replicable, and annually r epeated groups, using the same nests (usually in trees) for years at a time. Herons maintain nests free of regurgitated prey parts and nestl ing fecal materials by discarding detritus and fecal sacs over the nes t edge. This behavior produces a ''rain'' of fecal matter including id entifiable discarded or undigested items (e.g., bones) that reflect th e food on which herons prey. Collecting this material provides a quant ifiable estimate of contaminants in the food web (Fitzner et al. 1982) and makes the heron a prime sampling target (Fitzner et al. 1982; Car lile and Fitzner 1983; Hinds 1983). We discuss here the results of a t wo-year study designed to determine the relationship between heavy met al residues in heron fecal castings and those in heron tissues from th e same colonies. We also evaluated whether analysis of heron excrement was a reliable indication of heavy metals in the environment.