The bufflehead duck (Bucephala albeola) (Mergini) ranges from Alaska and Canada to the United States and Mexico. Buffleheads ingest invertebrates as a major component of their food throughout life. Puddle ducks (Anatinae) change mainly to vegetable foods at an early age. Loss of helminth parasite species and abundance in the fall migration has been reported for puddle ducks. This change in food has been hypothesized to cause some of the parasite loss. Nothing was known about helminth community dynamics in wintering buffleheads, including possible loss of helminths evident in puddle ducks. Helminth communities of the buffleheads were compared between wintering localities in the Chihuahua Desert of Texas and Mexico and to results from a nesting locality in Manitoba, Canada. There were no significant differences for average helminth species richness, prevalence, or abundance between the nesting and wintering grounds. Replenishment of helminths occurred in wintering buffleheads, and abundance of some helminth species increased significantly over time. The majority of helminth life cycles were indirect. These results were mostly related to the bufflehead's continued ingestion of invertebrate foods. Seven of the 41 helminth species present in buffleheads were in common to the 3 localities. Helminth community similarities between Manitoba and Texas and Manitoba and Mexico were much lower than similarity between Texas and Mexico. The dissimilarities were mostly attributable to differences in habitats but may also indicate loss of helminth species with subsequent infections with other species. The component community of the bufflehead from the Chihuahua Desert in Texas (n = 41) consisted of 23 species of helminths (10 species of cestodes, 7 trematodes, 4 nematodes, and 2 acanthocephalans) for a total of 4,008 individual specimens. Cestodes accounted for 69% of the total abundance. The component community of B. albeola from the Chihuahua Desert in Mexico (n = 26) consisted of 18 species of helminths (7 species of cestodes, 5 trematodes, 4 nematodes, and 2 acanthocephalans) for a total of 4,345 individual specimens. Cestodes accounted for 83% of the total abundance. The bufflehead shared 10 helminth species with other species of waterfowl utilizing habitats in the Chihuahua Desert. A checklist of all helminth parasites reported for buffleheads includes 27 identified to genera, 40 to species, and 12 species from buffleheads from the Chihuahua Desert in common with buffleheads from other localities.