Tick infestation of birds in grasslands experiencing woody plant encroachment in the United States Great Plains.

Abstract

Woody plant encroachment is one of the largest threats to grasslands of the US Great Plains. Its spread, mainly due to fire suppression, affects entire ecosystems, including arthropod vectors, bird communities, and the ecology of vector-borne disease. Eastern redcedar (Juniperus virginiana), one of the primary encroaching species in this region, is known to increase abundance of pathogen-carrying tick species such as Amblyomma americanum; however, the role birds play in carrying ticks in association with eastern redcedar encroachment is unknown. In areas of Oklahoma representing 3 stages of eastern redcedar encroachment, we mist-netted birds, sampled larval and nymphal ticks from them, and evaluated tick infestation of birds from May to October 2023. Of 140 birds sampled, 25.7% were infested with ticks, a higher prevalence of infestation than in most previous studies of birds in the United States. Notably, some birds were infested with Ixodes scapularis, which has rarely been found on wildlife other than reptiles in the southern US. There were no significant differences in prevalence or intensity of tick infestation in birds across differing levels of eastern redcedar encroachment, indicating that a high proportion of birds carry ticks in all encroachment stages. This study provides the first evidence that birds contribute to the ecology of tick-borne disease systems in grasslands experiencing woody plant encroachment. Our results, which suggest birds are likely moving ticks into, out of, and among eastern redcedar-encroached grasslands of the US Great Plains, can help inform land management and public health efforts seeking to reduce disease risk.