Causes of mortality of the Wyoming toad

Wyoming toads (Bufo baxteri) that died from January 1989 to June 1996 were submitted to the Wyoming State Veterinary Laboratory (Laramie, Wyoming, USA ) for postmortem evaluation. These consisted of 108 free-ranging toads and 170 animals from six captive populations. Ninety seven (90%) of 108 free-ra nging toad carcasses were submitted during September and October. From 1989 to 1992, 27 (77%) of 35 mortalities in the captive populations occurred in October, November, and December. From 1993 to 1996, mortality in captive t oads occurred without a seasonal pattern and coincided with changes in hibe rnation protocols that no longer mimicked natural cycles. Cause of mortalit y was determined in 147 (53%) of the 278 cases. Mycotic dermatitis with sec ondary bacterial septicemia was the most frequent diagnosis in 104 (71%) of 147 toads. Basidiobolus ranarum was found by microscopic examination of sk in sections in 100 (96%) of 104 of these mortalities. This fungus was isola ted from 30 (56%) of 54 free-ranging and 24 (48%) of 50 captive toads. This research documents the causes of mortality for both free-ranging and capti ve endangered Wyoming toads over a 7 yr period.