Trends of winter nutritional restriction, ticks, and numbers of moose on Isle Royale

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During a 7-year study, we monitored winter nutritional restriction of moose (Alces alces) and moose numbers on Isle Royale (winters 1987-88 to 1993-94). Over the 7 winters, the estimated moose population decreased 26% from an historic high of 1,653 (winter 1987-88) to 1,216 (1989-90), then increased to a new high (1,880 and 1,770) by winters 1992-93 and 1993-94. During that time, there was a significant (P = 0.0486) negative relation (r = -0.84) between the percent of urine specimens collected from snow (snow-urine) in late winter with urea nitrogen:creatinine (UN:C) ratios ≤3.5 mg:mg and percent change in the moose population from winter 1987-88. Mean urinary UN:C of moose residing on the east and west ends of Isle Royale declined (P ≤ 0.000), among years; however, slopes of the 2 trends were different (P = 0.0001). The nutritional restriction and decline in moose numbers appeared to involve an epizootic of the winter tick (Dermacentor albipictus; indicated by percent moose observed with tick-induced hair breakage and loss). During winters 1987-88 to 1989-90, the percentage of late winter snow-urine specimens with UN:C ratios indicative of severe nutritional restriction ranged from 47 to 58%; however, the percentage decreased to zero by winter 1993-94 as the tick infestation subsided and moose numbers increased.

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Journal of Wildlife Management