Lyme Disease and Migrating Birds in the Sant Croix River Valley

Over 9000 migrating birds representing 99 species from the St. Croix River Valley, a Lyme disease-endemic area of east-central Minnesota and northwestern Wisconsin, were examined in 1987. Two-hundred and fifty deer tick larvae and nymphs infested 58 birds from 15 migrant species; 56 of the ticks were positive for the Lyme disease spirochete Borrelia burgdorferi. Five ground-foraging migrant bird species favoring mesic habitats accounted for nearly 75% of the parasitized individuals. Almost half of the spirochete-positive ticks were removed from migrating birds collected in a riparian floodplain forest. Birds may be both an important local reservoir in the upper Mississippi Valley and long-distance dispersal agents for B. burgdorferi-infected ticks to other regions.