Acanthocephalan parasitism in the Western Bluebird (Sialia mexicana).

Acanthocephalan parasites of the species Plagiorhynchus (Prosthorhynchus) formosus Van Cleave, 1918, were recovered from the intestinal tracts of two male and two female wild Western Bluebirds (Sialia mexicana). Parasitism by P. formosus was considered to be a contributory cause of death of these breeding adult bluebirds. This is the first reported recovery of acanthocephalan parasites from Western Bluebirds.