Experienced beekeepers can tell the state of a colony by listening to the bees – if they are agitated, angry, hungry, or calm. Bees generate sound through their body movements, wing movements, and high-frequency thoracic muscle contractions. The bee's body acts as a sounding board, amplifying these vibrations into a hum, and by doing this they broadcast information about their activities, mood and behaviors. Tapping into these audio signals offers incredible insights to the health and status of a colony.
The BeeHero In Hive Sensor takes periodic recordings of a hive, which are then analyzed to detect audio ‘signals’ that might indicate changing behaviour or status. The 2 key features of the sound we are interested in are the sound frequency (measured in Hertz), and volume. The frequency of sound waves is heard by humans as pitch; a higher frequency creates a higher pitch. Honey bees produce many frequencies of sound – from less than 50Hz to more than 1000 Hz. We analyze the amount of noise (or energy) produced at different frequencies, and how this changes over time. In our research apiaries we track the audio profile of hives of different strengths, and also how this changes in response to different events such as queenless, swarming, and hive treatments etc. Thus over time we can associate unique audio ‘signatures’ with different events or changes in colony status.
A good way to visually represent the sound of a hive is to use an audio ‘heat map’, called a spectrogram (See figure 1 below). Colour is used to represent the amount of noise generated by the colony at various frequencies over time - ranging from deep blue for very quiet/low energy, to dark red for very loud/high energy. Figure 1 shows the spectrograms of 2 different colonies during almond pollination 2023. Colony A was a weak, failing colony, whereas Colony B was a strong healthy colony.
You can see clear differences in both the amount of noise produced between the two colonies (Colony B is significantly louder) and the frequency range over which the noise is generated (measured in Hz on the vertical axis). Colony B generates a strong signal in 2 distinct frequency bands, whereas Colony A produces only sporadic noise at lower frequencies. These are 2 contrasting hives, but useful to exemplify how we can interpret the sounds of the bees.
Audio monitoring of honey bees is an evolving science, but our knowledge is improving all the time, as is the range of colony insights that we can generate by listening to the bees. This article is intended to outline the basic principles of audio monitoring, we’ll include a more detailed review of specific audio signatures and behaviors in future newsletters.