Cadmium-induced calcium stress in natural populations of White-tailed Ptarmigan in Colorado

Recently, an isolated population of White-tailed Ptarmigan ( Lagopus leucurus) was discovered in the San Juan Mountains of Colorado with unusually brittle bones. The affected birds inhabit an area that contains high levels of several potentially toxic trace metals, prompting two questions. (1) Are metals somehow responsible for the brittle bone problem in ptarmigan? (2) Are the conditions that produced this bone abnormality widespread in Colorado? I used a multidisciplinary approach to answer these questions. I evaluated the environment for metals, traced metals through the ptarmigan food chain, and evaluated ptarmigan tissues for the presence of metals and for damage. I also compared the life histories of affected ptarmigan with those living elsewhere in Colorado.; Biochemical analyses of ptarmigan foods revealed that cadmium was biomagnified by willow, a common ptarmigan food. Mean cadmium level in willow (stems, leaves, and leaf buds) was 2.63 μg/g - dw. Cadmium also was accumulated in ptarmigan renal and hepatic tissues—not just in the brittle-bone population, but throughout a broad section of central and southwestern Colorado. Kidney-Cd accumulations were markedly age dependent and ranged from 0.2 to 188 μg/g - ww. Forty-six percent of adult ptarmigan in Colorado had kidney-Cd levels above the toxic threshold (100 μg Cd/g) for birds. Cadmium-induced nephrosis (mononuelear interstitial inflammatory cell infiltrates and dilated tubules surrounded by attenuated epithelium) was detected in 57% of adult ptarmigan tested. Adult ptarmigan with kidney-Cd levels above the toxic threshold had bone calcium levels 8 to 10% lower than ptarmigan with non-toxic kidney-Cd levels.; Cadmium-affected ptarmigan on Treasure Mountain, Colorado, showed lower individual bird fitness than the baseline for this species. Clutch sizes were 17% lower in the cadmium-contaminated population. Reproductive success was lowest among 3 and 4+ hens. The basic replacement rate (R_o) for the study population was only 0.53, yielding an intrinsic rate of natural increase (r) of about −0.24, and a λ of 0.8. From 1997 to 2000 the cadmium-contaminated population on Treasure Mountain was a “sink” and was maintained by recruitment from nearby, presumably less contaminated areas.; These studies suggest that cadmium may be having heretofore, unrecognized effects on terrestrial ecosystems, throughout much of central and southwestern Colorado. The degree to which these problems are linked to mining in the area was not determined.