Range expansion of blacklegged ticks in New Brunswick and the role of grouse as dispersal agents

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University of New Brunswick


The geographic range of blacklegged ticks (Ixodes scapularis) has been expanding northward into once previously inhospitable regions, where climate was thought to be a barrier to population establishment. Although the ticks are present in New Brunswick, Canada, and the phenomenon has been studied in the past, the ecological drivers for their range expansion have not yet been identified. It has also been proposed that ground dwelling forest birds may play an integral role in maintaining a reservoir of tick-borne pathogens and serve to disperse the ticks short and long distances. Most studies have focused on the roles of white-tailed deer, rodents, and migratory birds in blacklegged tick ecology, however I investigated the potential of two non-migratory ground dwelling forest birds, ruffed grouse (Bonasa umbellus) and spruce grouse (Falcipennis canadensis), to disperse blacklegged ticks and maintain a reservoir of tick-borne pathogens. This was the first study to detect numerous breeding populations (i.e., where larvae were present) of blacklegged ticks in New Brunswick and significantly expand New Brunswick Department of Health Lyme disease risk maps. Generalized linear models fit with climatic characteristics and forest metric variables highlighted the importance of climate metrics and forest characteristics on larvae abundance, densities, and presence. Additionally, ruffed and spruce grouse showed no evidence of active tick-borne pathogens, Borrelia burgdorferi or Anaplasma phagocytophilum, or of past B. burgdorferi infections. It is possible that both grouse species, like other Galliformes, have superior immune responses to these pathogens and thus are not suitable reservoir hosts, however it does not explain the absence of antibodies associated with B. burgdorferi.