Modeling the role of songbirds and rodents in the ecology of Lyme disease

Small rodents such as the white-footed mouse (Peromyscus leucopus) and the eastern chipmunk (Tamias striatus) efficiently transmit Borrelia burgdorfer i, the etiologic agent of Lyme disease, to feeding ticks, whereas other hos ts of ticks are less efficient reservoirs of B. burgdorferi. We examined th e roles of ground-foraging and ground-nesting songbirds as alternative host s for ticks, focusing on their potential to dilute the infection prevalence of ticks (Ixodes scapularis, the black-legged tick) with B. burgdorferi. W e developed a mathematical model based on the relative use by ticks of rode nt and bird hosts across varying host densities. We parameterized the model for sites in southeastern New York State using original data and for the n ortheastern United States using published values. Our results indicate that American robins (Turdus migratorius), ovenbirds (Seiurus aurocapillus), ve eries (Catharus fuscescens), and wood thrushes (Hylocichla mustelina) have a low capacity to dilute the prevalence of tick infection, particularly whe n rodents are at moderate to high densities. We attribute this result to lo w use by ticks of birds and a low density of birds relative to that of rode nts. Only when rodents constitute less than ca. 10-20% of the combined rode nt and songbird host community are birds capable of substantially reducing the infection prevalence of ticks. In years or habitat types in which the d ensity of rodents is low but that of ground-dwelling songbirds is high, the risk of human exposure to Lyme disease may reduced because birds dilute th e infection prevalence of tick vectors.