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AUTHORS: William J. Severud, University of Minnesota; Glenn D. DelGiudice, Minnesota Department of Natural Resources; Tyler R. Obermoller, University of Minnesota
ABSTRACT: Recruitment is an important driver of population dynamics. Northeastern Minnesota’s moose population has declined ~55% from 2006 to 2016. Our research was initiated because survival and specific causes of mortality of calves were largely unknown. We placed GPS collars on neonates 2013–2014 to estimate survival, cause-specific mortality, and space use of calves and their dams, but due to an executive order we were precluded from collaring in 2015. Using an alternate method involving behavioral cues from already collared moose and helicopter surveys, we continued the study. Survival of calves in 2013–2016 dropped precipitously to 60% in the first 30 days of age. Thirty-one of 40 calves (77.5%) died by 9 months of age in 2013–2014. Surveys indicated 56% mortality by 6 months of age in 2015, yet only an additional 4% mortality between 6 months and 11 months of age (60% mortality). Hazard (instantaneous probability of death) for calves was initially low, but peaked at ~20 days of age, coincident with peak energetic demands on dams due to lactation. In 2013–2014, 84% of mortalities were due to wolves or black bears, the ratio of wolf- to bear-kills at 4:1. In 2015 and 2016, we investigated instances of cow behavior indicative of calf mortality, resulting in discovery of 16 wolf-kills, 3 bear-kills, 3 unknown predator-kills, and 1 vehicle collision, yet many calves were assigned unknown fate. Tracking cow movements was a reliable way to estimate calving in all years and to a lesser degree calf mortality in 2015 and 2016. Identifying causes of calf mortality and understanding their relations to various landscape factors should yield insight into mechanisms contributing to the declining population and serve as a basis for an ecologically sound management response.
