# Winter Carbon Dioxide Measurement in Honeybee Hives
###### Abstract  
Sensor technologies have sufficiently advanced to provide low-cost devices that can quantify carbon dioxide levels in honeybee hives with high temporal resolution and in a small enough package for hive deployment. Recent publications have shown that summer carbon dioxide levels vary throughout the day and night over ranges that typically exceed 5000 ppm. Such dramatic changes in a measurable parameter associated with bee physiology are likely to convey information about the colony health. In this work, we present data from four UK-based hives collected through the winter of 2022/2023, with a focus on seeing if carbon dioxide can indicate when colonies are at risk of failure. These hives have been fitted with two Sensirion SCD41 photacoustic non-dispersive infrared (NDIR) carbon dioxide sensors, one in the queen excluder, at the top of the brood box, and one in the crown board, at the top of the hive. Hive scales have been used to monitor the hive mass, and internal and external temperature sensors have been included. Embedded accelerometers in the central frame of the brood box have been used to measure vibrations. Data showed that the high daily variation in carbon dioxide continued throughout the coldest days of winter, and the vibrational data suggested that daily fanning may be responsible for restoring lower carbon dioxide levels. The process of fanning will draw in colder air to the hive at a time when the bees should be using their energy to maintain the colony temperature. Monitoring carbon dioxide may provide feedback, prompting human intervention when the colony is close to collapse, and a better understanding may contribute to discussions on future hive design. honeybee; carbon dioxide; NDIR; SCD41; accelerometer; vibration; hive scale; fanning; precision beekeeping; precision apiculture; smart hive +
Footnote †: journal: Medical  
the colony population. Daytime changes in the measured mass can provide an estimate of the number of foraging bees in the colony. In the winter, the mass will decrease with the consumption of stored food resources and the colony size decrease. The internal hive temperature is also a clear indicator of colony health, as the bees will maintain a temperature of around 34 \({}^{\circ}\)C in brood-rearing areas of the hive. A weakening of the colony is shown when they are unable to keep this temperature stable. Widespread use of hive scales and temperature monitoring has grown, to the extent that there are now many suppliers of commercial hive monitoring products [25; 26; 27; 28; 29]. Many of these products send data directly to cloud-based data storage and provide web-based methods to track the colony health and issue warnings; for example, if the mass changes dramatically due to theft or a brood box is blown over in the wind. Beyond mass and temperature, measurements of different gasses have also been reported as part of the drive to what has been termed precision apiculture and smart hives. Humidity--water vapor in its gaseous state--is known to play a vital role in the development of the brood [30]. The measurement of humidity is readily available in low-cost, small capacitive sensors that provide an appropriate accuracy both in digital and analogue formats. Digital devices often incorporate a temperature measurement in the same package, as well as undertaking the analogue to digital conversion on the sensor chip. Easily deployable, these sensors can be purchased on breakout boards starting for as little as EUR 5, with the raw chips costing significantly less. Many of the devices incorporate i2c interfaces, each with different addresses, allowing some spatial variation over a hive to be monitored with relatively simple and inexpensive hardware. Investigations into the effect of humidity have been extensively reported, including from hives in the field made with small, embedded sensors [31; 32; 33; 34].