Nutrient Peak Shifts in the Arctic Implications for Migratory Herbivores Under Climate Change

Aim: Quantifying how the timing and spatial variability of Arctic vegetation nutrient peaks are projected to shift under climate change, and assessing potential consequences for migratory herbivores that rely on seasonal synchrony with peak plant quality. Location: Circumpolar Arctic, with emphasis on tundra regions. Time Period: Projections to the end of the 21st century, under SSP2-4.5 and SSP5-8.5 climate scenarios. Major Taxa Studied: Migratory herbivores. As a case study, we use long-distance migratory herbivorous birds to represent species reliant on synchrony with Arctic vegetation phenology and to illustrate differences in timing flexibility. Methods: We developed a novel method to convert Leaf Area Index (LAI) outputs from Earth System Models (ESMs) into Normalised Difference Vegetation Index (NDVI), allowing estimation of the day of year when vegetation reaches peak quality (the nutrient peak). We then used this method across multiple CMIP6 models and climate scenarios to map projected changes in timing and variability of nutrient peaks. These projections were compared to observed timing flexibility in bird migration. Results: Nutrient peaks are projected to advance across most of the Arctic, with the strongest shifts in Europe–western Russia, where tundra regions may experience advances of up to 19.1 days by 2100. These advances are accompanied by increased spatial heterogeneity and interannual variability. Comparing projections to data on migratory timing of long-distance migratory birds suggests that several species may already experience a mismatch between migration timing and timing of nutrient peaks by mid-century. Under SSP5-8.5, nearly all years are likely to show timing mismatches by century's end, even for species with broader behavioural flexibility. Main Conclusions: Climate-driven shifts in Arctic vegetation phenology are expected to increasingly disrupt the match between peak plant quality and migratory herbivores' resource demand. As mean conditions move beyond historical variability and extreme years become more frequent, migratory species may need to undergo major shifts in timing or routes to remain synchronised with a rapidly changing Arctic.