Trip durations and distributions
In total, 5576 drone trips and 16850 foraging trips were recorded with 177 drones and 281 foragers in June and July 2022. The drones made an average of 3.04 trips per day and the average trip duration was 16.8 ± 10.4 min. The foragers made an average of 8.2 trips per day and the average trip duration was 32.8 ± 35.9 min. The trip duration of the drone flights showed a bimodal distribution, dividing the drone flights into short trips and long trips (Fig. 1). The peak of the short trips was at 2.5 min, and the peak of the long trips was at 19.02 min, indicating that the most frequently observed short trip duration was approximately 2.5 minutes and the most frequently observed mating trip duration was approximately 19 minutes. The intersection point was at 7.6 min, a value that correlated well with previously reported lower limit of mating flight durations (Koeniger and Koeniger 2007; Woodgate et al. 2021), and trips of duration of 7.6 minutes and longer were defined as mating flights from here on. Forager flights showed a right-skewed distribution with a long tail to the right that tapered off to zero at around 150 min and the peak was at 9.6 min, indicating that the distribution of longer foraging trips tapered off more slowly than the distribution of shorter trips, most foraging trips were shorter than 150 minutes, and the most frequently observed foraging trip duration was approximately 9.6 minutes.
Comparing the distribution of each of the first several trips of the day led to revelation of an interesting drone flight behavior (Fig. 2). Because the average trip number per day was 3.04 for the drones and 8.2 for the foragers, the comparison was conducted with the first four trips of the drones and the first nine trips of the foragers. The majority of the first flights the drones made were the short trips, but the distribution significantly shifted towards the long trips in the second flights, and by the third flights of the day, the majority of the flights were long trips. In contrast, forager trips showed no such shift in distribution. The height of the peak significantly lowered from trip one to trip nine, which was expected, as there were fewer trips in trip nine, but the distribution pattern remained similar from trip one through trip nine.
Daily Trip Numbers
Both the drones and the foragers made trips every day, as the local weather is known to be mild during the mating season (Fig. 3). However, the flight activities of the drones varied from day to day, as demonstrated by the ANOVA analysis comparing the daily average trip numbers from d1 to d20 in June. Of the 190 comparisons comparing the daily average total trip numbers, 93 were statistically signficant. Of the 190 comparisons comparing the daily average mating trip numbers, 114 were statistically different. No statistically significant differences were observed for the foragers. The number of detected bees decreased over time as tags were lost or removed by other bees, or bees were lost due to aging, predation, drifting or other factors. Notably, there was a complete lack of mating trips on d7, d11 and d17. Referencing the weather conditions on those days showed that a lack of mating trips correlated with a sharp drop in temperature and an increase in clouds (Table 1). Since drone mating flights begin shortly after noon and continue for several hours, the weather data from noon to 6pm were used.
Table 1
Daily (12-6pm average) climate data
|
Temperature (°F)
|
Humidity
(%)
|
Wind
(mph)
|
Clouds
|
D1
|
73.4
|
46.8
|
3.1
|
sunny
|
D2
|
72.0
|
50.1
|
3.6
|
partly cloudy
|
D3
|
74.8
|
54.8
|
3.8
|
partly cloudy
|
D4
|
80.5
|
36.7
|
2.7
|
partly cloudy
|
D5
|
89.1
|
37.5
|
3.4
|
sunny
|
D6
|
85.2
|
42.1
|
3.6
|
sunny
|
D7
|
73.7
|
66.0
|
3.4
|
mostly cloudy to partly cloudy
|
D8
|
72.8
|
37.9
|
3.0
|
sunny
|
D9
|
81.1
|
31.8
|
2.9
|
sunny
|
D10
|
76.8
|
42.8
|
3.8
|
sunny
|
D11
|
69.2
|
46.8
|
4.1
|
partly cloudy
|
D12
|
67.6
|
41.4
|
2.9
|
partly cloudy
|
D13
|
68.7
|
39.9
|
3.6
|
partly cloudy to sunny
|
D14
|
78.3
|
33.2
|
2.8
|
sunny
|
D15
|
81.8
|
36.3
|
3.1
|
sunny
|
D16
|
95.1
|
16.3
|
2.0
|
sunny
|
D17
|
83.6
|
35.7
|
2.7
|
partly cloudy
|
D18
|
81.7
|
42.8
|
2.9
|
sunny
|
D19
|
79.7
|
47.5
|
2.9
|
sunny
|
D20
|
76.2
|
50.4
|
3.1
|
sunny
|