Abstract

Information on long-term natural mortality of free ranging mountain lions (Puma concolor) in the Pacific Northwest has not been available. From January 1994 to August 2004, we mapped locations of mountain lion mortalities using geographic information system technology and examined available carcasses from mortalities of a study of 103 radio collared mountain lions (51 males, 52 females) on a 518-km² study area in the southern Cascade Mountains of Oregon (USA). Full or partial necropsy examinations were done on 34 adult and 27 subadult/kittens (36 male, 25 female) that died during the study. Causes of mortality were divided in 10 categories including legal and illegal hunting, trauma, predation, parasites, and natural disease and infection. The two highest causes of mortality for the 34 adult carcasses examined were parasite (nodular stomach worms) and disease related lesions, each accounting for seven deaths. Nodular stomach worms (Cylicospirura spp.) were associated with large ulcerative granulomas of the pyloric region of the stomach, which resulted in hemorrhage and peritonitis. When both adults and subadults (n=61) are considered, eight mortalities (13.1%) were attributable to these parasites and ten to other diseases (16.4%). On an annual basis, the percentage of deaths attributable to a single mortality category would vary. In 1994, a public referendum, which prevented the use of dogs for hunting cougars, was passed. Immediately after the referendum, illegal harvest was the most important mortality factor until later in the study when parasites and disease became the highest single causes of death. On-going research is being conducted to further define the role of the parasite Cylicospirura in cougar ecology and health.