Assessing Calf Survival and the Quantitative Impact of Reproductive Success on the Declining Moose (Alces americanus) Population in Northeastern Minnesota
Minnesota Department of Natural Resources, Doctoral Dissertation Fellowship
Neonatal survival and recruitment are important drivers of population growth. The moose (Alces americanus) population in northeastern Minnesota has declined ~55% from 2006 to 2016. Survival patterns and specific causes of mortality of calves were largely unknown in this study area. We placed GPS collars on neonatal moose in 2013 and 2014 to estimate survival, cause-specific mortality, and space use of calves and their mothers. 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 dropped precipitously to 58% by 30 days of age in 2013 and 2014, and then to 34% by 9 months of age. Median age of death of calves that died before 1 year of age was 17.5 days. Hazard started low at birth and spiked at ~20 days old. Similar patterns were seen in 2015, with a 30-day survival rate of 63% and 10-month survival rate of 40.5%. Over-winter survival was generally high in all 3 years. We will model population trajectory using our observed demographic rates and those from the companion adult moose mortality project. Predation was the leading cause of calf mortality in 2013 and 2014, with 84% of mortalities due to wolves (Canis lupus) or black bears (Ursus americanus). Predation was an important cause of mortality in 2015 as well, but the relative certainty in assigning cause was low. Calves were generally preyed upon once the dam and calves departed their calving sites. Wolf predation was the leading cause of calf mortality in our study. We will also examine fine scale habitat factors (hiding cover, forage availability, canopy closure, etc.) at calving sites, peak lactation sites, and mortality sites. Identifying specific causes of calf mortality and understanding their relations to various landscape characteristics and other extrinsic factors should yield insight into mechanisms contributing to the declining moose population in northeastern Minnesota and serve as a basis for an ecologically sound management response.