During the 1999 and 2000 spring and summer seasons, we collected and analyzed 544 eggs, 273 from background sites and 271 from mining sites to measure and compare selenium (Se) levels. We collected and analyzed eggs from 31 avian species. Our data indicated an increase in Se levels in birds on mining sites, i.e., 16 of 24 species (67%) had significantly higher Se levels. The remaining species did not have large enough sample sizes for statistical tests. For all eggs collected on mining sites, the distribution of Se levels was as follows: 57% were less than 5 ppm, 30% were between 5 and 10 ppm, 8% were between 10 and 16 ppm, and 5% were >16 ppm. We concluded that relatively few birds (i.e., <8%) that occupied habitats associated with mining activity in southeast Idaho have Se levels that exceed the threshold level recommended by Adams et al. (2002). In 2001 we obtained reproductive data on 298 American robin (Turdus migratorius) nests and 325 red-winged blackbird (Agelaius phoeniceus) nests. Analysis included nest success, clutch size, hatching success, fledging success, egg weight, and neonate weight. Thus, we had 12 measures of reproduction for comparison between mining and background sites. We found no significant difference between sites for 11 of these measures. The remaining measure, nest success for robins, was significantly higher in mining sites.
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Vol. 70 • No. 2