Fatal clostridial infections and clostridial toxicoses are common in birds. Most fatalities are associated with toxin production and progress rapidly, often within 24 hours of infection. We describe an unusual and protracted course of disease in 6 captive brown pelicans (Pelecanus occidentalis), which was believed to result from toxicosis by toxovar A produced by a mixed infection with Clostridium sordellii and Clostridium perfringens. Although the first death in the group occurred 3 days after signs of illness were documented, the remaining birds died over a 38-day period despite aggressive antibiotic and supportive therapy. Although the birds presented with classic signs of botulism, Clostridium botulinum was not identified in any tissues or environmental samples. Postmortem findings in all pelicans included extensive subacute myonecrosis, enteritis, and nonsuppurative hepatitis. Alpha-toxins and sordellilysin genes from C perfringens and C sordelli isolates, respectively, were detected via polymerase chain reaction. The source of the pathogenic bacteria was sediment within a water basin inside the affected birds' enclosure.