During a 3-yr comprehensive study, 196 ixodid ticks (9 species) were collected 
from 89 passerine birds (32 species) from 25 localities across Canada to 
determine the distribution of avian-associated tick species and endogenous Lyme 
disease spirochetes, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt, 
and Brenner. We report the following first records of tick parasitism on avian 
hosts: the rabbit-associated tick, Ixodes dentatus Marx, from Manitoba and 
Ontario; the mouse tick, Ixodes muris Bishopp and Smith, from British Columbia; 
and the blacklegged tick, Ixodes scapularis Say, from New Brunswick. Moreover, 
we provide the first record of the Neotropical tick, Amblyomma humerale Koch (1 
nymph), in Canada and its parasitism of any bird. This tick was compared 
morphologically with nymphs of other Neotropical Amblyomma spp., and 
genetically, using a 344-bp fragment of the 12S rDNA sequence of 41 New World 
Amblyomma species. The first collections of the western blacklegged tick, Ixodes 
pacificus Cooley and Kohls, from passerine species in Alberta and British 
Columbia, are also reported. Notably, we further report the first isolation of 
B. burgdorferi from the bird tick, Ixodes auritulus Neumann, collected from an 
American robin, Turdus migratorius L., on Vancouver Island. Furthermore, B. 
burgdorferi-positive I. auritulus larvae were collected from a 
reservoir-competent fox sparrow, Passerella iliaca (Merrem). Our findings 
indicate that ground-dwelling passerines, in particular, are parasitized by 
certain ixodid ticks and play an important role across Canada in the wide 
dispersal of B. burgdorferi-infected ticks and increased risk of Lyme disease 
exposure.