An application of upscaled optimal foraging theory using hidden Markov modelling: year-round behavioural variation in a large arctic herbivore

• Published in: Movement Ecology
• Main Authors: Larissa T. Beumer, Jennifer Pohle, Niels M. Schmidt, Marianna Chimienti, Jean-Pierre Desforges, Lars H. Hansen, Roland Langrock, Stine Højlund Pedersen, Mikkel Stelvig, Floris M. van Beest
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2020
• Subjects: Hidden Markov modelling; Behavioural state classification; Seasonality; Activity budgets; Arctic ungulate; Optimal foraging theory; Biology (General); QH301-705.5; Arctic; Greenland; muskox; ovibos moschatus
• Online Access: https://doi.org/10.1186/s40462-020-00213-x; https://doaj.org/article/5eb2c2b0b9064427bc6edea6f1d5238c

Abstract Background In highly seasonal environments, animals face critical decisions regarding time allocation, diet optimisation, and habitat use. In the Arctic, the short summers are crucial for replenishing body reserves, while low food availability and increased energetic demands characterise the long winters (9–10 months). Under such extreme seasonal variability, even small deviations from optimal time allocation can markedly impact individuals’ condition, reproductive success and survival. We investigated which environmental conditions influenced daily, seasonal, and interannual variation in time allocation in high-arctic muskoxen (Ovibos moschatus) and evaluated whether results support qualitative predictions derived from upscaled optimal foraging theory. Methods Using hidden Markov models (HMMs), we inferred behavioural states (foraging, resting, relocating) from hourly positions of GPS-collared females tracked in northeast Greenland (28 muskox-years). To relate behavioural variation to environmental conditions, we considered a wide range of spatially and/or temporally explicit covariates in the HMMs. Results While we found little interannual variation, daily and seasonal time allocation varied markedly. Scheduling of daily activities was distinct throughout the year except for the period of continuous daylight. During summer, muskoxen spent about 69% of time foraging and 19% resting, without environmental constraints on foraging activity. During winter, time spent foraging decreased to 45%, whereas about 43% of time was spent resting, mediated by longer resting bouts than during summer. Conclusions Our results clearly indicate that female muskoxen follow an energy intake maximisation strategy during the arctic summer. During winter, our results were not easily reconcilable with just one dominant foraging strategy. The overall reduction in activity likely reflects higher time requirements for rumination in response to the reduction of forage quality (supporting an energy intake maximisation strategy). ...