Abstract

Topic: Moose management and monitoring

Determinants of Moose (Alces alces) Calf Weights in Sweden: Regional Patterns and Temporal Trends

Carolin Berndt¹, Wiebke Neumann², Robert Spitzer², Håkan Sand³, Fredrik Widemo²

SLU, Skogmarksgränd 17, 907 36 Umeå, Sweden
SLU, Department of Wildlife, Fish, and Environmental Studies, 901 83 Umeå, Sweden
SLU, Department of Ecology, Grimsö forskningsstation 739 93 Riddarhyttan, Sweden

Abstract
Body weight is a fundamental life-history trait influencing individual fitness, reproductive success, and population dynamics in large herbivores. In moose (Alces alces), early-life growth is particularly critical, as calf weight is closely linked to survival probability, future reproductive potential, and overall population viability. Understanding the environmental and biological determinants of this trait is essential for effective wildlife management, especially in the face of changing climatic and habitat conditions. This study investigates temporal trends and regional variation in moose calf weights across Sweden from 2012 to 2024, utilizing over 228,000 individual calf weights across the country. Key environmental drivers, including weather conditions, forage availability and intra- and interspecific competition, were analysed alongside moose population parameters such as sex ratio, female body weight, and reproductive metrics (e.g., calves per female) to assess their relative importance in shaping calf growth patterns. Results reveal a distinct north–south gradient, with calves in southern Sweden exhibiting lower body masses than those in the north. While calf weights in southern regions show a declining trend over time, those in the north remain relatively stable, albeit with interannual variation within regions. The factors influencing calf weight vary geographically. While female body mass and young forest availability are expected to play a role nationwide, weather conditions and other environmental variables may have region-specific effects on growth dynamics. These findings underscore the complex interactions among climatic, ecological, and demographic factors shaping moose populations. They highlight the need for region-specific management strategies to mitigate declining calf weights. Further research on the interplay between climate change, forest management, and moose population dynamics will be crucial for ensuring the long-term sustainability of Sweden’s moose populations.