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Temperature, Not Day Length, Drove the Muskox Summer Metabolic Shift

Close-up of a muskox in snow
Research · Physiology

A study published on 29 April 2026 followed nine adult female muskoxen (Ovibos moschatus) living in the wild near Zackenberg in northeast Greenland over multiple years to examine how metabolism and activity change through the seasons. The animals carried GPS collars with activity sensors and intraruminal transmitters that recorded rumen temperature and heartbeat vibrations, allowing the researchers to estimate stationary heart rate without repeatedly handling the animals.

Stationary heart rate remained around 35 beats per minute for most of the year, then began to rise in mid-May and reached about 68 beats per minute in July, an increase of roughly 94%. Rumen temperature increased by about 0.5 °C, from around 38.8 to 39.3 °C, while locomotor activity rose by about 75%. Activity peaked in late June, while heart rate and rumen temperature peaked around mid-July.

Temperature, not day length, triggered the summer shift

The seasonal transition did not simply follow day length. During the part of the year when daylight was rapidly increasing, the physiological measurements remained relatively stable while ambient temperatures stayed well below freezing. Once continuous daylight had arrived, stationary heart rate and the other measurements rose strongly as temperatures increased, with the clearest change as ambient temperature approached 0 °C from below.

The metabolic shift reverses winter energy conservation

During the long winter, muskoxen conserve energy and draw on stored reserves. The short summer is their opportunity to rebuild those reserves. The researchers interpret the temperature response as a way to align this period of fat accumulation with the variable start of the Arctic growing season.

Sources and image credit

  1. Schmidt, N. M., Hansen, L. H., Grøndahl, C., Tahas, S., Bertelsen, M. F., Fohringer, C., Leonard, A., & van Beest, F. M. (2026). Seasonal shifts in muskox metabolic rates and energy expenditure are primarily governed by ambient temperature. Proceedings of the Royal Society B: Biological Sciences, 293(2069), 20260121. https://doi.org/10.1098/rspb.2026.0121Primary peer-reviewed research article, published 29 April 2026. Multi-year physiological and activity measurements from nine wild muskoxen in high-Arctic Greenland showed that the seasonal metabolic transition was primarily associated with ambient temperature rather than photoperiod.

Image: ilovegreenland / Visit Greenland, via Wikimedia Commons / Flickr. Muskox photographed 22 January 2004; representative species photograph, not a study animal. Cropped to 16:9. CC BY 2.0: https://creativecommons.org/licenses/by/2.0/ · CC BY 2.0 · Source

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