The effect of bovine tuberculosis and brucellosis on reproduction and survival of wood bison in Wood Buffalo National Park

1. Wood bison (Bison bison athabascae L.) abundance in Wood Buffalo National Park, Canada, declined from an excess of 10 000 bison in the late 1960s to a low of 2200 bison in the late 1990s. 2. Bovine tuberculosis (Mycobacterium bovis) and brucellosis (Brucella abortus), were introduced to Wood Buffalo National Park in the late 1920s. As each of these pathogens has the potential to reduce survival and reproduction in bison, they are suspected to have played a role in the decline in bison abundance. 3. We live-captured bison in the winters of 1997-2000, tested for tuberculosis, brucellosis and pregnancy and released animals with radio transmitters to evaluate survival. 4. We found that bison that were positive for both diseases were less likely to be pregnant or to survive the winter than bison positive for one or neither disease. Further, in one population, bison that were tuberculosis-positive had a substantially lower pregnancy probability. 5. Demonstrating a negative effect of diseases on survival and reproduction is a necessary, but not sufficient, test of the role of diseases in bison population decline.