DDT Contamination of Migrating Birds Using White-faced Ibis as an Indicator Species

摘要

A species of concern to Naval Air Station Fallon (NASF) and other military installations in Nevada, Utah, California, and Oregon is the White- faced ibis (Plegadis chihi). These long-legged wading birds feed primarily on invertebrates in the wetlands and irrigated croplands on and surrounding military lands and military operating areas (MOAs). Earnst et al. (1998) state that concern for the species is centered around its small population size and the limited and dynamic nature of its breeding habitat. The U.S. Geological Survey (USGS) and Nevada Department of Wildlife (NDOW) have documented that pesticide contamination occurs in a Great Basin breeding population of the White-faced ibis (Henny and Herron 1989, Henny 1997). A significant segment of the ibis population at Carson Lake, Nevada (adjacent to Naval Air Station Fallon) is burdened with high levels of DDE, the principal metabolite of DDT. A chlorinated hydrocarbon compound widely deployed as a pesticide after the Second World War, its use in the U.S. was banned in 1972. It remained in use elsewhere, including Mexico, although our southern neighbor announced in 1997 that such applications would be completely phased out by 2007. The contamination of ibis at Carson Lake is of a magnitude that threatens reproductive success. Historically, this has resulted in eggshells that were 18% thinner than normal and a 20% decrease in breeding production. DDE levels are highest among the initial nesting cohort, the contamination persists today, and it has been determined that these contaminants are not being acquired in western Nevada. Where and how these birds are being contaminated with DDT was unknown, so wildlife and environmental managers could not take substantive steps toward conserving this population. An increase in eggshell thinning by just 2% could result in extensive reproductive failure, and that could place this species' population on a direct path for listing under the Threatened and Endangered Species Act.