Diverse individual energy-budgeting tactics within wild populations provide resilience to natural fluctuations in food availability and expenditure costs. Although substantial heterogeneity in activity-related energy expenditure has been documented, few studies differentiate between responses to the environment and inter-individual differences stemming from life history, allometry, or somatic stores. Using tri-axial accelerometry, complemented by diet analysis, we investigated inter-individual within-season variation in overall dynamic body acceleration (ODBA; activity intensity measure) and “Activity” (above an ODBA threshold) in a high-density population of European badgers (Meles meles). Weather (including wind speed) affected ODBA and activity according to predictors of earthworm (food) availability and cooling potential. In spring, maximal ODBA expenditure at intermediate rainfall and temperature values suggested that badgers traded foraging success against thermoregulatory losses, where lower-condition badgers maintained higher spring ODBA irrespective of temperature while badgers in better body condition reduced ODBA at colder temperatures. Conversely, in summer, lower-condition badgers modulated ODBA according to temperature, likely in response to super-abundant food supply. Between 35% (spring, summer) and 57% (autumn) of residual total daily ODBA variance related to inter-individual differences unexplained by seasonal predictors, suggesting within-season tactical activity typologies. We propose that this heterogeneity among individual energy-expenditure profiles may contribute to population resilience under rapid environmental change.

The range of food resources consumed by opportunistic carnivores is shaped by habitat-specific availability and productivity. However, baseline data on the diet of the Japanese weasel (Mustela itatsi) in managed wetland habitats remain scarce. Firstly, we conducted a diet study examining Japanese weasel scats from the Watarase-yusuichi wetland (WYW) (September 2024–August 2025). Based on 103 fecal samples, we calculated seasonal frequency of occurrence (FO) for 16 food categories and estimated their relative volume (RV) using the point-frame method. Surprisingly, plant material and fruit seeds were eaten frequently across seasons, and fruit seeds constituted a major component of scat volume, particularly in summer. Secondly, we compared baseline WYW data with published datasets from two contrasting aquatic habitats (a suburban river area and a rice paddy landscape) using harmonized categories and multivariate analyses. Diet composition differed markedly among study sites, and the PERMANOVA analysis indicated a significant effect of sampling site (R² = 0.643, p = 0.001) with a weaker seasonal effect (R² = 0.208, p = 0.038), with no significant pairwise differences between seasons (all p ≥ 0.300). Although cross-site comparisons should be interpreted cautiously because datasets were collected in different decades (1998, 2018, and 2024–2025), these findings support habitat-associated trophic plasticity in the Japanese weasel, with dietary shifts across habitats and seasons apparently reflecting variation in available food resources. In managed floodplain wetlands such as WYW, maintaining a mosaic of reed beds, ponds, and channels may help sustain dietary flexibility and population persistence in this species.

Assessments of animal vulnerability to climate change often emphasise climatic exposure, yet the magnitude of environmental change alone cannot determine whether populations persist. Animals have evolved behavioural, physiological, phenological, and spatial responses that can sustain survival and reproduction under variable conditions, although their effectiveness depends on energetic demands, resource availability, ecological interactions, and other anthropogenic pressures. In this review, we develop an animal-centred mechanistic framework linking climatic conditions to individual responses, demographic outcomes, and wider ecological consequences. We examine how climatic variability and extremes interact with evolved characteristics, including body size, energy storage, and reproductive strategies, and how differences among individuals can either buffer populations or alter their composition through selective effects. Crucially, responses that maintain demographic performance under prevailing conditions may incur costs or erode the capacity to cope with subsequent change, while apparent population stability can conceal declining reproductive potential or altered ecological relationships. We therefore propose that climatic resilience depends not simply on whether animals can compensate for current conditions, but on whether they retain the biological and ecological capacity to respond to future challenges. This perspective provides a mechanistic basis for distinguishing vulnerability from exposure and identifying opportunities and limits for conservation intervention.