Abstract

Topic: Movements and habitat use

Hot Moose Summer: Behavioral response of wild moose to ambient temperature and heat stress in Minnesota summers

Michelle Carstensen¹, Amanda McGraw², Andrew Tri², Deahn DonnerWright³

Wildlife Health Program, Minnesota Department of Natural Resources, 5463 West Broadway, Forest Lake, MN 55025, US
Forest Populations and Research Group, Minnesota Department of Natural Resources, Grand Rapids, Minnesota, 55744
USDA Forest Service, Northern Research Station, 5985 Cty Hwy K, Rhinelander, WI, 54501

Abstract
The moose (Alces alces) population in Minnesota experienced a rapid decline in the past 20 years. Climate change has been listed as one of the potential underlying causes via direct (e.g., physiological changes) or indirect (e.g., behavioral changes) effects. Recent research using rumen boluses to measure internal body temperature of moose reported a significant relationship with maximum daily ambient temperatures in summer, such that heat stress events were more likely to occur at temperatures >25°C. This research further suggested that moose survival was adversely impacted by the number of times a moose experienced heat stress on an annual basis. To better understand moose physiological responses to increasing ambient temperatures, we also aim to understand if there is a paired behavioral response as well. We were interested in how habitat selection of 161 wild adult moose (115 females, 46 males) varied over 5 summers (2013–2017) using a machine-learning approach. We evaluated how moose used the landscape in relation to a temperature threshold of >25 C⁰, biomass (kg/ha) of preferred browse species, age at capture, sex, and cover type. The most important variables were biomass of preferred browse, mixed forests, woody wetlands, evergreen forests, and deciduous forests. Overall, moose used areas with more biomass of preferred browse species, and bulls used areas with slightly higher browse biomass than cows. In summer, it appeared that moose used forested cover types that typically have closed canopies and provide shade. Specifically, moose used mixed forest less than expected given availability on the landscape, while using woody wetlands and evergreen forests more than expected. We also investigated the behavioral state of moose in relation to habitat and temperature (both ambient and internal body temperature) on a subset of 41 individuals (23 females, 18 males). We used accelerometer data and GPS locations to evaluate habitat use and what behaviors occurred (resting, foraging, and traveling inferred using Dirichlet regression methods) prior to, during, and after heat stress events. Moose must make behavioral tradeoffs to mitigate heat stress, especially in the summer, and those tradeoffs may reduce overall fitness and impact survival.