CHAMPAIGN, Ill. –Songbird species that carry the ticks responsible for Lyme disease and other diseases forage close to the ground in large wooded areas, according to a recently published study by Christine Parker, a graduate research assistant at the University of Illinois’ Prairie Research Institute, Illinois Natural History Survey.
Researchers studied songbirds and their foraging habitats to determine which environmental factors affect bird-tick encounters and the dispersal of ticks in Illinois. Birds are known to move ticks long distances and play a role in spreading the black-legged tick (Ixodes scapularis), a primary vector of Lyme disease.
Along with her colleagues, Parker (who conducted this study for her master’s research in the Department of Natural Resources and Environmental Sciences at the University of Illinois) set up mist nets in 22 forested areas in Champaign, McLean, Piatt, Putnam, and Vermilion Counties. They trapped birds twice in fall and again in spring over three years.
Researchers examined the birds’ heads and necks where ticks are most likely to be found because birds are unable to effectively groom these areas. During the study, the scientists captured and released 1,077 birds of 83 species.
Of the species studied, 42 percent were infested with at least one tick. Nearly 370 ticks were found on 136 (13 percent) of the birds captured.
“These numbers are fairly typical of what we would expect to see on birds in forested areas in central Illinois,” Parker said. “None of the birds had a large infestation.”
Birds with the largest number of ticks included the white-throated sparrow, Northern cardinal, and gray catbird. About 20 percent of ticks found were the black-legged tick.
The most important factor influencing bird infestation by ticks was the height above the forest floor at which birds forage, Parker said. Birds that forage closest to the ground were most likely to have ticks, since ticks live on the ground and in low vegetation, surviving on moisture from the underbrush.
The researchers expected higher infestation rates in patches where invasive shrub cover was relatively high. Invasive species such as honeysuckle and multiflora rose form a dense understory with abundant fruit and cover for wildlife, and also suitable conditions for the black-legged and other tick species. Instead, the researchers found that as the vegetation cover increased, tick infestation among captured birds declined. Parker suggested that the fruit grows across the crown of these shrubs, which may reduce tick-bird interactions if ticks are searching for hosts at lower levels below shrub crowns.
Tick infestations were also more prevalent among birds captured in large forest plots compared with smaller plots, likely because tick populations tend to flourish where there are abundant deer and other large animals available for blood meals.
“It is important for people to be aware that migratory birds move ticks, and thereby pathogens, into areas where ticks were previously not established,” Parker said. “Just because Lyme disease isn’t a problem in one area doesn’t mean that disease-carrying ticks won’t inhabit that area in the future.”
The study was published in the Journal of Medical Entomology.
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