## 3 Results and Discussion
### Study Goal
#### 3.2.2 Bombus  
Bumble bees' different acoustics behaviour in the colony and in the field could contain information that aids our understanding and ability to monitor these important pollinators. While some researchers investigated the acoustics in the field for flight [46; 80; 88; 90] and buzz-pollination analysis [81], others used in-colony acoustics for foraging activity [84; 85], defence [108] (reaction to mammalian breath and CO2-enriched air), dominance [97] (fundamental frequencies between 300-400 Hz), and thermoregulation [109] (broadband acoustic signal with fundamental frequencies between 180-200 Hz) monitoring [97]. The relationship between \"buzz-pollination\" and \"floral sonication\" has been investigated in measures of duration, frequency, and amplitude in [91]. The results showed that airborne recordings of sonication vibrations in _B. impatiens_ characterize duration and frequency faithfully while acoustic amplitude (relative peak amplitude and sound pressure level) are not correlated with vibrational amplitude. Detecting different species of bees is another research area that has increased interest recently. This information is useful in both agricultural production and ecological research, as it helps to understand and protect the biodiversity of these important pollinators and their habitat and also evaluate the pollination services. Authors in [80], for example, designed a system to distinguish the flight sounds of three pollinating bee species in Japan (i.e., _Apis mellifera_, _Bombus ardens_, _Tetalonia nipponensis_) and one hornet species (i.e., Japanese yellow hornet, _Vespa simillima xanthoptera_, a predator of honeybees in Japan. Results showed clear differences in the spectra of these sounds, in MFCCs and in fundamental frequency; classification was performed by a support vector machine (SVM) classifier. Using acoustic properties such as peak amplitude, peak frequency, and duration to identify different species of bumblebees during \"buzz-pollination\" or \"floral sonication\" (bees vibrating flowers) has been the aim of some studies [81; 83; 99]. The results showed that body shape or wing size can be correlated with fundamental frequency [81], and also duration of the buzzes was shown to differ with body size (larger bees producing shorter buzzes) in six different species of bumblebees (_B. hortorum_, _B. lapidarius_, _B. psucorum_, _B. pratorum_, _B. terrestris_, _and_ B. lucorum_) [99]. Moreover, using amplitude, frequency, and duration of flight and \"floral sonication\" sounds of 15 pollinating bee species (see Table 4) on _Solanum lycopersicum_ flowers showed that the sonication sounds are more relevant to bee species recognition as the machine learning algorithms reached an accuracy of 73.4% on sonication and 64% flight sounds, respectively [83]. In fact, detection of foraging activity has also been explored to provide insight into pollination service [85; 86]. The work in [86], for example, used microphones installed in front of the colony entrance of three different species of bumblebees (_B. psucorum_, _B. humilis_ and _B. hymorum_) to detect arrival and departure of the bees. The daily histogram of departure on each day showed that there are different foraging habits in different species. _B. psucorum_ were mostly active around noon and in the afternoon, while less active in the morning. On the other hand, _B. hymorum_ were more active after 3 p.m. Another interesting observation was that light rain in the afternoon made _B. humilis_ workers stay inside, but it did not affect _B. hymorum_. Moreover, inspired by computational auditory scene analysis (CASA), the work in [46] used focal templates to recognize audio segments which contained buzzes. To discriminate between arrivals and departures, an algorithm based on the maximum absolute difference between two consecutive peaks of the smoothed signal envelope were used. Classification of arrival and departures reached sensitivity and precision levels of 95%. In [85], in turn, the foraging activity of the _B. sylvicola_ and _B.