Colonial wading birds as bioindicators of food chain contamination by heavy metals and organohalogens: Relationship among tissue concentration, growth rates, and reproduction

Technologically advanced countries use more than 10,000 chemicals routinely and approximately 1,500 new chemicals are introduced annually (Connell and Miller 1984). While many of these chemicals are harmless, some have catastrophic effects on aquatic ecosystems and show the most severe effects on higher trophic level consumers, including wading birds through bioaccumulation and biomagnification (Ohlendorf et al. 1979, Spalding et al. 1994). The present study is the first to address three primary questions: (1) Can non-sacrificial sampling of wading birds reflect food chain contamination reliably? (2) Are nestling growth rates or other reproductive indices of the birds affected by food chain contamination? (3) Are reproductive indices related to tissue concentrations of contaminants in these birds?;Tissues of White Ibis (WI) and Little Blue Herons (LBH) were sampled from a colony of wading birds near Devil's Swamp, an area known to be polluted with organochlorines and heavy metals, and from four other colonies as controls. Eggs, blood, guano, and food samples were analyzed for hexachlorobenzene, hexachlorobutadiene, lead, and cadmium contamination. Eggshells and feathers were also tested for metal content. LBH chicks were measured twice weekly to ascertain growth rates.;The data indicate for the first time that food chain contamination by heavy metals can be readily assessed from guano samples collected from chicks of both WI and LBH, and demonstrate differences in metal contamination between polluted and control colonies. This was not true for organochlorine contaminants, which were distributed independently of the metals in the environment. These data are also original in establishing a relationship between the presence of cadmium in feathers and reduced growth rates in LBH, and in demonstrating that lead-exposed chicks had increased nestling mortality. The findings of the present study expand our understanding of wading birds as indicators of environmental contamination in several ways: (1) non-sacrificial sampling can reflect food chain contamination by heavy metals; (2) nestling survival and growth rates are affected by exposure to heavy metals in the food chain; and (3) wading birds bioaccumulate metals and their tissues can thus serve as reliable bioindicators of contamination.