12.2. Tracking unmarked bees
Although foraging activity can be inferred from overall colony weight gains or losses measured with precision balances (Meikle et al., 2008), hive entrance activity is a more reliable parameter. The advantages of this method are:
- Registration of most departing or arriving bees.
- Straightforward measuring of daily
The major disadvantages, however, are
- Not all of the bees entering the hive have foraged (some bees do not even take off).
- Accumulation of large datasets during a relatively
brief observation period.
A straightforward approach for automatic registration uses photoelectric relays which are connected to a single or to multiple tunnels. Bees are forced to pass through the tunnels, where they are detected while leaving or entering the hive. Various constructions have been developed during the last five decades. A commercial counter is produced by Lowland Electronics bvba (Belgium). This device is attached to the hive entrance and uses 32 parallel tunnels such that it can cope with bee trafficking in full colonies. The registration of bees is direction-specific, because two relays are positioned in sequence within each tunnel. Thus, the system can differentiate between bees leaving the colony and those entering the colony. It allows estimating the number of bees outside the colony at each given moment, so that bee losses can be calculated at the end of the day. The device has been used in a number of studies (Struye et al., 1994; Struye, 2001). It was generally found to be reliable if it was attended to carefully, particularly by frequent checking and cleaning of the tunnels. This method allows for correlating hive entrance activity with different external parameters such as precipitation, temperature, sunshine etc. In addition, it can detect substantial bee losses. However, the system is unable to track individuals or groups of individuals. Therefore, in experimental studies, the basic statistical unit is a single colony. This requires a sufficient number of colony replicates.