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Aim: Long‐term population studies provide invaluable insights into natural variability, particularly in ecology and conservation. We reconstruct the 31‐year dynamics of the European hamster population in a vast area within Central Europe. We identify key meteorological factors influencing population dynamics and project the potential impact of climate change on their conservation. Location: Poland. Methods: As an indicator of hamster population changes, we utilized data on the prey of the Lesser Spotted Eagle (Clanga pomarina) collected over 31 years (1993–2023) in the geographical region where the European hamster coexists. The reliability of ornithological data was validated. Results: Meteorological factors play a critical role in driving hamster population changes. We found a strong correlation between population growth and warm weather patterns in October and November, as well as favourable conditions in March of the following year. These weather patterns allow hamsters to store larger food supplies and enter hibernation in better physiological condition, resulting in improved habitat and nutritional conditions upon emergence from hibernation in spring. Main Conclusions: Our findings underscore the importance of considering meteorological factors in conservation risk assessments, especially when planning and evaluating hamster reintroduction programmes. The significant influence of meteorological conditions raises concerns about the future prospects of this species in the context of ongoing climate change. Disturbances during critical hamster periods, including unseasonal and prolonged temperature drops in spring following relatively warm winters, pose substantial risks to conservation efforts. [ABSTRACT FROM AUTHOR]

Animals in urban areas often encounter novel and potentially stressful conditions. It is important to understand how wildlife cope with anthropogenic disturbance. To investigate this specific adaptation we live-trapped squirrels in two study sites in Warsaw: a forest reserve and an urban park and we estimated stress responses at three levels: long-term and medium-term stress (the level of stress hormones, i.e. cortisol and cortisone concentrations, in hair and feces) and acute reaction to human-induced stress (measured during handling with the aid of the three indices: breath rate, struggle rate, and vocalization). According to GLMM models no difference in the stress hormones level was found between the two populations. The only differences in cortisol concentrations clearly depended on the season, i.e. being higher in autumn and winter comparying to other seasons. There was no influence of sex, or reproductive status on stress hormones. Forest squirrels had significantly higher breath rates, suggesting they were more stressed by handling. There was no difference in the struggle rate between study areas, this index was mostly affected by season (i.e. being highest in winter). First-trapped squirrels vocalized less than during the subsequent trappings. Assumingly, during the first, and more stressful trapping, squirrels used 'freezing' and/or little vocalization, while during next captures they used alarm calls to warn conspecifics. Overall, we showed that the two squirrel populations differed only in terms of their breath rate. This suggests that they did not differ in medium-term and long-term stress in general, but they can differ in acute response to handling. This also suggests that both populations were similarly affected by environmental factors. The lack of clear effects may also be due to population heterogeneity. Thus, in order to assess the effects of anthropogenic stressors a broader range of indicators and diverse analytical methods, including behavioral analyses, should be employed. [ABSTRACT FROM AUTHOR]