We examined the phylogenetic distribution of cytochrome b haplotypes of the avian blood parasite genera Haemoproteus and Plasmodium across the migratory divide of the Swainson's thrush (Catharus ustulatus) in British Columbia, Canada. From 87 host individuals, we identified 8 parasite haplotypes; 4 of Plasmodium and 4 of Haemoproteus. Six haplotypes were novel; 1 Haemoproteus haplotype was identical to H. majoris found in the blue tit (Parus caeruleus) in Sweden, and another halotype was identical to a Plasmodium haplotype found in the white-crowned sparrow (Zonotrichia leucophrys) in Oregon. The 2 most abundant parasite haplotypes were widely distributed across the contact zone, whereas 2 other parasite haplotypes seem to have structured distributions. Compared with 74 Plasmodium and Haemoproteus haplotypes published in GenBank, haplotypes recovered from Swainson's thrushes do not form monophyletic groups, and they are closely related to haplotypes from a variety of other hosts and localities. In addition, we recovered 2 Swainson's thrush Plasmodium haplotypes from the nonmigratory orange-billed nightingale thrush (Catharus aurantiirostris) in Costa Rica. This study is the first to elucidate avian blood parasite transmission, distribution, and phylogenetic relationships in an avian contact zone in North America.