Changes in an exurban bird assemblage and the phenology of ticks (Acari: Ixodidae) on birds: a comparison of three sampling periods between 1984 and 2019

The blacklegged tick (Ixodes scapularis Say) has undergone range contractions and expansions since its origination half a million years ago and is expanding in all cardinal directions. These changes affect the range of several tick-borne diseases. Birds host larval and nymphal I. scapularis and may contribute to the local distribution of ticks in the environment. Furthermore, bird migration and dispersal provide mechanisms for the rapid range expansion of ticks and their pathogens. We examined data spanning 35 yr to evaluate changes in the bird assemblage and the seasonal occurrence of ticks on birds from 1984 to 1985, 2010 to 2011, and 2019. The five most abundant bird species changed across sampling periods. Bird species that hosted ticks during each sampling period and where at least five individuals hosted ticks in one sampling period were the American robin (Turdus migratorius Linnaeus), black-capped chickadee (Poecile atricapillus L.), blue jay (Cyanocitta cristata L.), gray catbird (Dumetella carolinensis L.), northern cardinal (Cardinalis cardinalis L.), song sparrow (Melospiza melodia Wilson), white-throated sparrow (Zonotrichia albicollis Gmelin), and wood thrush (Hylocichla mustelina Gmelin). The infestation intensity and prevalence of ticks on birds generally increased over time and appear to be driven by a rise in I. scapularis larvae. Finally, bird species predicted the number of I. scapularis larvae per bird and the proportion of birds carrying I. scapularis larvae. Birds may be increasingly important in the local maintenance and long-distance dispersal of I. scapularis, given the rise in the infestation intensity and prevalence of I. scapularis larvae.