A long-term study of contaminant effects on cavity-nesting birds in New Mexico

Background/Question/Methods

Since 1996, we have studied the effects of contaminants on reproductive parameters of western bluebird (Sialia mexicana) and ash-throated flycatchers (Myiarchus cinerascens) populations nesting across a contaminant gradient at Los Alamos National Laboratory, New Mexico.  We have evaluated reproductive success in relation to soil contamination levels in the individual home range.  Eggs were analyzed for PCBs, heavy metals, and radionuclides and prey remains were collected from study nests to determine the potential contaminant uptake from the home range.  We measured nesting success, fledging success, fluctuating asymmetry, parasitism, and immunocompetence of nestlings over the 12 years.

Results/Conclusions

Nestling sex ratios varied from 0 to 100% females and were compared to clutch size, environmental and climatic determinants simultaneously with locations of concern for exposure to contaminants.  In addition, we have compared reproductive success to environmental variation, such as a three-year drought and a large-scale wild fire which caused a significant decrease the cell-mediated immune response in nestlings.   Since 1996, the western bluebird has continued to reproduce several days earlier with every year.  Band-recapture data are used to investigate adult and nestling survival compared to locations and environmental variables and survival was found to be significantly reduced by the drought of 2000-2002 in New Mexico.