Impact of intestinal coccidiosis on the American goldfinch, Carduelis tristis.

Opinion on the virulence of parasites in their native hosts has ranged from extreme severity to avirulence. Recent theoretical work suggests selection on the parasite favors a range of outcomes depending on the life cycle of host and parasite, and implies that widely distributed parasites of moderate virulence would be more likely to affect host distribution and abundance than those at either extreme of virulence. American goldfinches, Carduelis tristis, are commonly infected with parasitic protozoa, particularly intestinal coccidians in the family Eimeriidae. Because of the high prevalence of the parasites, and the documented pathogenicity of coccidiosis in stressed captive birds, it seemed appropriate to examine the effect of these parasites on wild hosts at various stages in the host's life cycle. Goldfinches were captured in Washtenaw County, Michigan, and examined for intestinal coccidians. Two species, Isaspora exserta and Atoxoplasma latum, were found and described as new. Natural infection of adult birds with these and other parasites was not correlated with condition at capture, nor with thermogenic performance under cold stress. Experimental infection of adult goldfinches had minimal effects on dietary energy assimilation. However, experimental infection of nestling goldfinches resulted in reduction of body mass at fledging and reduced the fat reserves of fledglings. If coccidiosis exerts any regulatory effect on goldfinch populations, such effects should be sought among nestlings and fledglings rather than adults.PhDBiological SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104661/1/9542901.pdfDescription of 9542901.pdf : Restricted to UM users only