Wintering area DDE source to migratory white-faced ibis revealed by satellite telemetry and prey sampling

Abstract

Locations of contaminant exposure for nesting migratory species are difficult to fully understand because of possible additional sources encountered during migration or on the wintering grounds. A portion of the migratory white-faced ibis (Plegadis chihi) nesting at Carson Lake, Nevada continues to be exposed to dichloro-diphenyldichloroethylene (DDE) with no change, which is unusual, observed in egg concentrations between 1985 and 2000. About 45 to 63% of the earliest nesting segment shows reduced reproductive success correlated with elevated egg concentrations of > 4 µg/g wet weight (ww). Local prey (primarily earthworms) near nests contained little DDE so we tracked the migration and wintering movements of 20 adult males during 2000-2004 to determine the possible source. At various wintering sites, we found a correlation (r 2 = 0.518, P = 0.0125, N = 11) between DDE in earthworm composites and DDE in blood plasma of white-faced ibis wintering there, although the plasma was collected on their breeding grounds soon after arrival. The main source of DDE was wintering areas in the Mexicali Valley of Baja California Norte, Mexico, and probably the adjacent Imperial Valley, California, USA. This unusual continuing DDE problem for white-face ibis is associated with: the long-term persistence in soil of DDE; the earthworms' ability to bioconcentrate DDE from soil; the proclivity of white-faced ibis to feed on earthworms in agricultural fields; the species extreme sensitivity to DDE in their eggs; and perhaps its life history strategy of being a "capital breeder". We suggest surveying and sampling white-faced ibis eggs at nesting colonies, especially at Carson Lake, to monitor the continuing influence of DDE.

Aquatic and terrestrial stressors in amphibians: A test of the double jeopardy hypothesis based on maternally and trophically derived contaminants

“…This is particularly true for migratory species, which may rear young in habitats distinct from adult feeding or over-wintering grounds. For example, migratory white-faced ibis (Plegadis chihi) produce eggs contaminated with dichlorodiphenyldichloroethylene at uncontaminated nesting grounds [1]. Contamination of the eggs was traced to prior exposure of foraging parents in distant wintering habitats and resulted in reduced reproductive success [1].…”

Conservation Objectives for Wintering and Breeding Waterbirds in California's Central Valley

“…Conservation needs focus on securing habitat and reliable water for colony, foraging, and roosting sites; managing for open, early successional marshes favored for nesting; and providing incentives, as needed, to growers to maintain flood-irrigated crops and pastures and to promote practices (e.g., organic) that favor earthworms or other key ibis prey (Shuford 2014a; Table 7). Contaminants are also an issue for some ibis populations (Yates et al 2010).…”

Wintering ecology of sympatric subspecies of Sandhill Crane: Correlations between body size, site fidelity, and movement patterns

“…Although there appear to be no studies of the effects of contaminants on breeding White-faced Ibis in BCR 32, there is some evidence of eggshell thinning and cracked eggs in the Sacramento Valley (references in Yates et al 2010). Although DDT/DDE contamination in ibis eggs currently is generally relatively low at many colonies in the West, it remains elevated at colonies such as Carson Lake, Nevada, Cibola NWR, Arizona, and the Finney Lake Unit of Imperial Wildlife Area in the Imperial Valley, California (Yates et al 2010).…”

“…Although DDT/DDE contamination in ibis eggs currently is generally relatively low at many colonies in the West, it remains elevated at colonies such as Carson Lake, Nevada, Cibola NWR, Arizona, and the Finney Lake Unit of Imperial Wildlife Area in the Imperial Valley, California (Yates et al 2010). At Carson Lake there is continued evidence of lowered reproductive success correlated with elevated concentrations of DDE in eggs , King et al 2003, Yates et al 2010.…”

“…Satellite telemetry of blood-sampled ibis and an evaluation of earthworms collected at ibis wintering sites indicated that a wintering area near the California-Mexico (Imperial ValleyMexicali Valley) border was the likely source of the comparatively high DDE concentrations found in a segment of the ibis population nesting at Carson Lake (Yates et al 2010). By contrast, many of the Carson Lake ibis with low to medium DDE concentrations in their blood were wintering in areas of the Central Valley (both Sacramento and San Joaquin valleys) with low to medium DDE concentrations in earthworms.…”