Thermal responses of overwintering honey bee colonies to fondant feeding during mild winters and early springs

In the context of climate change, warmer winters and early-spring fluctuations alter overwintering conditions for honey bee colonies ( Apis mellifera ), increasing feed consumption, disrupting the winter cluster and advancing spring development. These changes increase the risk of winter mortality and can compromise spring crop pollination. Beekeepers use winter fondant feeding as an emergency measure, yet changes in hive microclimate in response to such interventions, documented with in-hive and ambient sensor data, remain largely undescribed.We report reproducible thermal responses to fondant feeding detected by a non-invasive Internet of Things (IoT) hive monitoring system across two winters: a mild winter/early spring in Ukraine (2018–2019) and an anomalously warm winter in Canada (2020). Fondant feedings were timed to winter warm spells and were followed by a sharp rise in in-hive temperature and a gradual decline over several days, accompanied by reduced in-hive relative humidity. We quantified responses as integrated areas of the temperature difference between in-hive and ambient temperature before and after feeding over 5- to 10-day windows. Response amplitude and decay duration were consistent across feeding events and depended on colony strength, suggesting that this integrated temperature difference may serve as a simple, non-invasive indicator of winter colony status, useful for emergency supplementation and preparation for early-spring pollination. To our knowledge, this phenomenon is documented here for the first time using IoT-based hive sensors as a rare but increasingly relevant pattern during warm winters, highlighting the potential of sensor-based monitoring to reduce winter bee mortality.