Borrelia burgdorferi sensu lato (s. l.) spirochetes are associated with a wide range of vectors and hosts. Birds are important hosts in the ecology of some hard ticks (Ixodidae) in northwestern Argentina, where B. burgdorferi s.l. have been detected in Ixodes pararicinus. We evaluated Borrelia infection in ticks collected from wild birds by molecular analysis through the presence of Borrelia DNA (by nested-PCR targeting the fla gene). A total of 381 ticks (357 larvae and 24 nymphs) belonging to four species (I. pararicinus, Haemaphysalis juxtakochi, Haemaphysalis leporispalustris and Amblyomma sp.) were collected. Partial sequences of the fla gene of Borrelia (100% identical to Borrelia sp. haplotype I from Argentina) were detected in 9 of 70 tick pools (6 pools of larvae and 1 pool of nymphs of I. pararicinus, and in 2 pools of H. juxtakochi larvae) collected on Turdus rufiventris, Syndactila rufosuperciliata and Troglodytes aedon. The results of this study suggest that resident birds have reservoir capacity for Borrelia sp. haplotype I.