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Kaldoaivi Reindeer Used More Mires and Shifted Diet Through the Snow-free Season

Reindeer in open summer landscape in Lapland, Finland
Research · Ecology

Semi-domesticated reindeer (Rangifer tarandus tarandus) in the Kaldoaivi/Gálddoaivi herding district of northern Finland changed both habitat use and diet through the snow-free season, according to a study first published in February 2026. Fifteen adult females were fitted with GPS collars in 2019, and 12 provided complete GPS and hair-isotope datasets for the combined analysis.

From spring and early summer to late summer and autumn, avoidance of rugged terrain weakened and use of mires and bogs increased. Greener areas were selected in both periods. Every analysed individual changed its selection for at least one habitat variable.

Hair isotopes showed a seasonal diet shift

Stable carbon and nitrogen isotopes in different sections of the animals’ hair also showed seasonal dietary change. Because hair grows over time, sections formed at different times retain isotopic signals from the forage eaten while they were growing. This allowed the researchers to compare diet from spring and early summer with diet from late summer and autumn.

The pattern was consistent with a shift from plants such as lichens, evergreen dwarf shrubs and deciduous woody vegetation toward forage such as sedges, grasses, horsetails and mushrooms that produced more enriched carbon and nitrogen isotope signals later in the season. The late-summer and autumn isotopic niche — the spread of isotope values used here as an indicator of dietary breadth — was also broader than in spring and early summer.

Habitat use and diet changed together

Habitat and diet changes were not completely independent. Among the habitat variables tested, how strongly individual reindeer reduced their avoidance of rugged terrain was the factor that showed a clear relationship with the direction of their dietary isotope shift. The authors interpret this link, together with the wider seasonal changes, as evidence of flexible foraging rather than fixed use of the same habitats and foods throughout the snow-free season.

They therefore classify the Kaldoaivi reindeer as habitat–diet generalists, while emphasising substantial individual variation in how foraging strategies changed between seasons.

Sources and image credit

  1. Hiltunen, T. A., Kivelä, S. M., Kumpula, J., Aspi, J. O., & Welker, J. M. (2026). Delineating seasonal shifts in reindeer habitat and diet selection by integrating GPS telemetry and stable isotope analysis. Wildlife Biology, 2026(3), e01570. https://doi.org/10.1002/wlb3.01570Primary open-access research article first published 2 February 2026 under CC BY 4.0. The study followed 15 adult female semi-domesticated reindeer in the Kaldoaivi/Gálddoaivi herding district in northern Finland during 2019; 12 individuals had complete GPS and hair stable-isotope datasets. From spring/early summer to late summer/autumn, avoidance of rugged terrain weakened, selection for mires and bogs increased, and isotopes indicated a dietary shift from plants such as lichens and shrubs toward sedges, grasses, horsetails and mushrooms. The authors classified the animals as habitat–diet generalists.

Image: Paasikivi / Wikimedia Commons — reindeer (Rangifer tarandus) in Lapland, Finland, 14 June 2014; representative Finnish summer image; cropped to 16:9 · CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ · Source

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