Why do queen bumblebees emerge from hibernation during weekends?

Climate-driven shifts in bumblebee emergence and flowering time can disrupt plant reproduction and affect pollinator health. To study such mismatches, accurate phenological data is crucial but challenging to collect, especially for pollinator hibernation emergence. Citizen science is increasingly being used to expand the spatial and temporal scope of data collection in research. Nevertheless, these data can be biased due to different reasons. We found that 33.14% of records in Europe and 32.47% in North America were gathered on weekends - exceeding what would be expected by random chance and showing opposite patterns to bumblebee museum specimen records. Bias also affected queen emergence date and varied by species, suggesting that species-specific traits may mediate the bias extent. We also present a case study showing how adjusting for day-of-the-week effects can change the statistical significance of temporal trends in bumblebee emergence dates. We thus recommend including the day of the week in statistical models to account for temporal biases. Our findings highlight the importance of correcting temporal biases in citizen science data to ensure accurate evaluations of ecological responses to climate change.