# Winter Carbon Dioxide Measurement in Honeybee Hives
## 3 Results  
Figure 2 shows the CO\({}_{2}\), in ppm (black), and temperature (blue) for colony HPP5 for the queen excluder (right) and crown board (left) starting on Tuesday 6 December 2022 at 11:48. This had the profile of a strong colony, with the temperature near the brood-rearing range at the queen excluder by day 100. There were few negative temperatures recorded in the hive even though external temperatures did fall below zero, and this was observed in other colonies during the same time and in close proximity. As previously reported [42], ambient air values of CO\({}_{2}\) (typically around 400 ppm to 450 ppm) were observed in the crown board during many of the first forty days, but not in the queen excluder. There were many days where the CO\({}_{2}\) exceeded 10,000 ppm in the brood box and on some days in the crown board, which is above the two supers, and thus more than 30 cm above the queen excluder sensor. Figure 3a shows the first week of the CO\({}_{2}\) data (black) shown in Figure 2 for the queen excluder. The hive mass on the same graph is the purple line. There was an interesting daily drop in mass that coincided with the fall in CO\({}_{2}\), which then rose again but not quite to the same level, as would be expected as provisions are expended by the colony in December/January. Typically, this change was between 50 g to 100 g, approximately corresponding to the mass of typically 500 to 1000 bees. While the change in mass for colony HPP5 could have been due to bees leaving the colony, the outside temperature was mainly below 10 \({}^{\circ}\)C, when the bees would not usually fly. Figure 2: The CO\({}_{2}\) (black) and temperature (blue) data for colony HPP5 for (**a**) the crown board and (**b**) the queen excluder starting on Tuesday 6 December 2022 at 11:48. To investigate if this fall and rise was connected to the CO\({}_{2}\), the mass changes were inspected for a colony that died at the start of the winter, colony HPP8. The mass changes for this hive are shown in the right-hand panel of Figure 3, and this exhibits the same sort of daily change but without the overall drop. It is, therefore, likely that the level of change was associated with changes in the wooden structure as the temperature fell at night and rose during the day, affecting the wood and its moisture content. Figure 4 shows that the crown board temperature tracked the external temperature, including going negative, but with a slightly higher value. The brood box maintained a much higher temperature, but even the queen excluder fell below 10 \({}^{\circ}\)C, below which bees are thought to cluster. Figure 5 shows the vibrational amplitude from colony HPP5, a strong colony, and colony HPP6, which was a weaker colony, as seen from the lower CO\({}_{2}\) levels in the hives and previous inspection data. For colony HPP5, the vibration amplitude did not clearly track the CO\({}_{2}\) levels, but for colony HPP6, this was more the case, suggesting that the  
Figure 4: The temperature in the brood box (blue), the crown board (red), and the external temperature (orange) for colony HPP5 starting on Tuesday 6 December 2022 at 11:48. Figure 3: (**a**) The CO\({}_{2}\) (black) and hive mass (purple) data for colony HPP5 for the queen excluder starting on Tuesday 6 December 2022 at 11:48. (**b**) The mass for colony HPP8 after the colony had died, showing the remaining daily mass variation in an empty hive. vibrational measurements picked up the increased activity, probably fanning, perhaps required to reduce the CO2 in the hive. This difference could be because the cluster was closer to the accelerometer in colony HPP6 than colony HPP5. Figure 6 shows the vibrational spectrogram for colony HPP6 using the same data as seen from days 0 to 7 in the left-hand panel of Figure 5. A spectrogram is a visual representation of the spectrum of frequencies of a signal as it varies with time, which has the frequency on the vertical axis and time on the horizontal axis.