Blood Parasite Prevalence and Intensity in Migrating and Non-migrating Raptors

Document Type


Publication Date

April 2010

Faculty Sponsor

Dr. Alfred M. Dufty, Jr.


The annual cycle of migration in many birds that breed in northern temperate regions is characterized by two migratory periods, a spring migration to a breeding site, and a fall migration to wintering site. Previous studies have shown that migratory birds have a higher prevalence of blood parasites than non-migratory birds. The hypothesis that the energetic demands associated with migration weakens the immune system and allows parasites to persist will be investigated through the analysis of blood composition changes of migrating raptors as compared to non-migrating ones. Host-parasite relationships affect the overall fitness of the host and also help us to understand the physiological and immunological constraints imposed on the host. This relationship also provides insight into ecological factors, such as distribution and abundance of hosts, parasites, and parasite vectors. Avian blood parasites have a negative effect on the fitness and survival of hosts, so given the physiological constraints imposed on hosts during migration, it is important to consider the host-parasite prevalence when assessing a bird’s fitness. During migration, September through October, we trapped American kestrels (Falco sparverius), sharp-shinned hawks (Accipter striatus), Cooper’s hawks (A. cooperi), northern goshawks (A. gentilis) and red-tailed hawks (Buteo jamaicensis) at the Idaho Bird Observatory in Boise, Idaho. We collected blood from the brachial vein to make blood smears. The avian parasites Haemoproteus, Leucocytozoon, and Plasmodium are present in Accipitradae and Falconidae, and we present data comparing intensities and prevalence of parasitism between migratory and non-migratory birds of different species. The results will help us to understand the link between blood parasite prevalence and the overall fitness of migrating raptors, and will also assist us in more fully understanding the physiological cost of migrating.

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