Moose mortality in northeastern Minnesota as a function of temperature
Mark S. Lenarz*, Minnesota DNR, Forest Wildlife Populations & Research Group, MN   
Michael E. Nelson, U.S. Geological Survey, Northern Prairie Wildlife Research Center , ND  
Andrew J. Edwards, 1854 Treaty Authority, MN  
Michael W. Schrage, Fond du Lac Resource Managment Division, MN 

Moose (Alces alces) are on the southern edge of their distribution in northern Minnesota 
and the dramatic decline of this species in northwestern Minnesota has been linked to 
increased summer and winter temperatures. Previous research has identified temperature 
thresholds in both summer and winter that trigger physiological responses to maintain body 
temperature. Recent research in northeastern Minnesota has documented high levels of 
non-hunting mortality, which varied seasonally and annually. To test for a link between 
mortality and temperature, we hypothesized that seasonal mortality would be a function of 
time above the temperature thresholds. We monitored 114 radio-collared moose over 5½ 
years to calculate mortality rates. We used Kaplan-Meier survival functions to calculate 
season mortality. We recorded ambient air temperature using temperature loggers. Summer 
temperature thresholds were exceeded from April to October with the greatest variability 
occurring in April and May. Non-hunting mortality in the "autumn" (1 August - 31 November) 
was linearly related to the number of days above threshold (threshold days) in the 
preceding April and May. Similarly, non-hunting mortality in "winter" (1 December - 28 
February) was linearly related to threshold days in the previous summer. The winter 
temperature threshold was exceeded in all months of the winter with the greatest variability 
in January. Non-hunting mortality in "spring" (1 March - 15 May) was linearly related to 
threshold days in January. These results suggest that non-hunting mortality may indeed be 
linked to warm temperatures during the summer and winter. Unless moose are able to 
better ameliorate the affects of warmer conditions in northeastern Minnesota, it is likely that 
we will see a northward shift in the distribution of this iconic species.
*Presenter