Avian conservation studies frequently evaluate the effects of anthropogenic factors like disturbance, habitat destruction, edge effects and environmental contamination. Host-parasite interactions are an often-overlooked aspect of avian conservation studies, despite the fact that parasites have the ability to dramatically affect host populations. The history of common loon ( Gavia immer ) conservation work has borne this out---many studies document the negative effects disturbance, habitat destruction and mercury have on loons, yet little is known about loon black fly parasites and nothing is known about loon blood parasites. I conducted a study to investigate the effects loon parasites have on nest success by testing the specificity of a black fly species, Simulium annulus , to the common loon, and by examining the haemosporidian fauna of loons. A series of bird decoys were presented on northern Wisconsin lakes to test the specificity of S. annulus to the common loon and to explore the importance of chemical and visual cues used for black fly host attraction. These tests revealed that S. annulus is a highly specific parasite of the common loon and that chemical cues are of significant importance in attracting black flies. Blood was collected from breeding loon pairs and their chicks to describe and examine the blood parasite fauna of a population of breeding loons. The genera Leucocytozoon and Plasmodium were successfully detected in loons using PCR techniques. Furthermore, both the presence and the intensity of Leucocytozoon infection in adult loons were significantly explained by loon blood mercury levels. These studies provide a detailed description of various loon parasites and show that mercury may be immuno-compromising these birds.
