Thomas Koert Lameris

Individual variation in avian migration timing is still poorly understood, yet recent evidence shows that it is closely linked to personality traits and may also be affected by food availability. Here, we examined how the interaction of the personality trait exploration speed and food availability affected the departure timing of Red Knots Calidris canutus from their wintering grounds. Using experimental manipulations of food access and measures of exploration speed in captivity followed by tracking of released individuals, we show that fast‐exploring birds departed later but only when subjected to restricted food access in the experiment, whereas birds with unlimited food access showed no personality‐dependent differences in departure timing. Our results suggest that personality does not reflect intrinsic variation in spring migration timing, but rather interactions with environmental variation affecting the birds' ability to refuel body stores after food restrictions.

Aim: To describe and compare the diets of an Arctic‐breeding shorebird, the Red Knot ( Calidris canutus ), across three geographically distinct breeding sites. We aimed to document the dietary patterns and identify key prey groups that characterise each population's foraging ecology. Location: Northwest Alaska (Nome), Northeast Greenland (Zackenberg) and North‐Central Russia (Taimyr Peninsula). Taxon: Red Knot (Aves: Calidris canutus ). Methods: We characterised chick diet by applying COI DNA metabarcoding to faecal samples and quantified local prey availability using standardised arthropod pitfall trap sampling at the three Arctic breeding sites. We described and compared the dietary composition, diversity, and relative abundance of major prey taxa among locations. Results: We found substantial geographical variation in the chick diet. Diptera was a major food source across all locations, but its constituent families and importance varied. In Taimyr, the diet was dominated by Tipulidae (crane flies), comprising nearly 50% of the relative read abundance (RRA). In contrast, chicks in Greenland consumed a diet dominated by Diptera (87.8%) that almost entirely lacked Tipulidae. The diet in Alaska was the most diverse, with balanced contributions from Diptera (28.5%), Coleoptera (22.3%), and Lepidoptera (23.2%), along with other invertebrate groups, including Agriolimacidae. Main Conclusions: The diet of Red Knot chicks differed among the study sites and appeared to be shaped primarily by the local availability of arthropod prey. This foraging plasticity allows the species to breed successfully across a wide circumpolar range with a heterogeneous prey landscape. However, this distinct specialisation on local prey, particularly Tipulidae in Taimyr, may create a critical phenological vulnerability.

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.

The timing of animal migrations is an interplay between migration programmes and physiological and environmental conditions. The rate of body store deposition underlies many timing options, with a key unresolved question being whether the rate of body store deposition and resource constraints limit advancements in migration departure. To study limits of deposition on departure timing, we captured red knots ( Calidris canutus islandica ) wintering in the Wadden Sea and manipulated hours of food access per day during spring body store deposition and prenuptial moulting phases. These birds were then released and tracked until spring migration departure from the Wadden Sea. When birds were allowed to feed more hours per day in captivity, they did not start body store deposition and plumage moult earlier, but gained stores faster, were heavier and had further progressed in prenuptial feather moult at the moment of release. After release, birds that had ad libitum access to food in captivity departed earliest from the Wadden Sea, and departure timing was explained by the rate of mass deposition in captivity. We experimentally demonstrate flexibility in the timing of annual‐cycle processes during spring migration. Red knots are flexible to adjust the rate of mass gain and moult to food availability, in turn allowing them flexibility in departure timing. This indicates that improvements in foraging conditions at staging sites will facilitate earlier departures, which will help migratory birds to keep pace with global warming. Read the free Plain Language Summary for this article on the Journal blog.

Recent observations of body size declines in animal populations have given rise to discussions of whether or not this is related to climate change‐induced temperature increases, with which the body size changes would follow Bergmann's rule. Although the debate is ongoing, the limited thermal benefits of currently observed size reductions make it unlikely that temperature increase shapes a direct selection pressure. Food constraints during early‐life development, which could be caused by mismatches between available resources and energetic demands, could cause smaller body sizes too. Here we investigate whether a decrease in body size, observed in a migratory shorebird, the red knot (Calidris canutus canutus) at their West‐African nonbreeding grounds over two decades, is linked to developmental plasticity during chick growth in the High Arctic. To do so, we combined datasets from both the wintering and breeding grounds on body size measurements (during chick growth and in fully grown juveniles), food availability, and diet inferred from stable isotopes deposited in feathers grown as chicks. From 2003 to 2021, stable‐isotope ratios revealed a decline in the dietary contribution of crane flies (Tipulidae, Diptera), the key food of growing chicks in the Arctic. On the breeding grounds, we observed that while the emergence of adult crane flies advanced along with earlier snowmelt dates, red knots did not adjust the timing of breeding, and this resulted in an increasing mismatch with the demands of growing chicks. As a result, chicks grew slower and, as observed on the wintering grounds, reached smaller final body sizes. Our results imply that increasing resource‐demand mismatches may lead to body shrinkage via plasticity during development. In this study, the increasing mismatch was linked with climate warming; the presented causal chain may explain other recent examples of body size reductions as well.

In the current warming climate, many organisms in seasonal environments advance their timing of reproduction to benefit from resource peaks earlier in spring. For migrants, the potential to advance reproduction may be constrained by their migration strategies, notably their ability to advance arrival at the breeding grounds. Recent studies show various changes in migration strategies, including wintering closer to the breeding grounds, earlier departure from the wintering grounds or faster travels by spending less time at stopover sites. However, whether such changes lead to earlier arrival or earlier breeding remains an open question. We studied changes in migration and reproduction timing in 12 populations of nine migratory birds, including seabirds, shorebirds, birds of prey and waterfowl breeding at Arctic sites bordering the Greenland and Barents Sea, a region undergoing rapid climate warming. The timing of migration and reproduction was derived from tracking and field data and analysed to study (1) how timing has changed in response to the changing moment of snowmelt at the breeding grounds and (2) what adjustments in migration strategies this involved. We found that in years with early snowmelt, egg‐laying in multiple populations advanced, but only two waterfowl populations also advanced arrival in the Arctic. In contrast, arrival in the Arctic generally advanced with time, even when snowmelt or egg‐laying dates did not advance. Earlier arrival with time was mostly explained by populations traveling to the Arctic faster, likely spending less time at stopover sites. Inability to forecast conditions in the Arctic may limit birds to adjust migration timing to annually varying snowmelt, but we show that several species, particularly waterfowl, are able to travel faster and advance the timing of migration over the years. The question remains whether this reflects adaptations to Arctic climate change or other factors, for example, environmental changes along the migratory route.

The timing of animal migrations is an interplay between migration programmes and physiological and environmental conditions. The rate of body store deposition underlies many timing options, with a key unresolved question being whether the rate of body store deposition and resource constraints limit advancements in migration departure. To study limits of deposition on departure timing, we captured red knots (Calidris canutus islandica) wintering in the Wadden Sea and manipulated food availability during spring body store deposition and prenuptial moulting phases, followed by release and automated tracking. With longer access to food in captivity, birds gained body stores faster and were heavier and further progressed in prenuptial feather moult, and after release departed earlier from the Wadden Sea. Our results show flexibility in migration decisions with an important role for food availability.

Herbivores are an integral part of Arctic terrestrial ecosystems, driving ecosystem functioning and sustaining local livelihoods. In the context of accelerated climate warming and land use changes, understanding how herbivores contribute to the resilience of Arctic socio-ecological systems is essential to guide sound decision-making and mitigation strategies. While research on Arctic herbivory has a long tradition, recent literature syntheses highlight important geographical, taxonomic, and environmental knowledge gaps on the impacts of herbivores across the region. At the same time, climate change and limited resources impose an urgent need to prioritize research and management efforts. We conducted a horizon scan within the Arctic herbivory research community to identify emerging scientific and management priorities for the next decade. From 288 responses received from 85 participants in two online surveys and an in-person workshop, we identified 8 scientific and 8 management priorities centred on (a) understanding and integrating fundamental ecological processes across multiple scales from individual herbivore–plant interactions up to regional and decadal scale vegetation and animal population effects; (b) evaluating climate change feedbacks; and (c) developing new research methods. Our analysis provides a strategic framework for broad, inclusive, interdisciplinary collaborations to optimise terrestrial herbivory research and sustainable management practices in a rapidly changing Arctic.