title: Stereoscopic motion analysis in densely packed clusters: 3D analysis of the shimmering behaviour in Giant honey bees.
abstract: BACKGROUND
  The detailed interpretation of mass phenomena such as human escape panic or swarm behaviour in birds, fish and insects requires detailed analysis of the 3D movements of individual participants. Here, we describe the adaptation of a 3D stereoscopic imaging method to measure the positional coordinates of individual agents in densely packed clusters. The method was applied to study behavioural aspects of shimmering in Giant honeybees, a collective defence behaviour that deters predatory wasps by visual cues, whereby individual bees flip their abdomen upwards in a split second, producing Mexican wave-like patterns.
  
  
  RESULTS
  Stereoscopic imaging provided non-invasive, automated, simultaneous, in-situ 3D measurements of hundreds of bees on the nest surface regarding their thoracic position and orientation of the body length axis. Segmentation was the basis for the stereo matching, which defined correspondences of individual bees in pairs of stereo images. Stereo-matched "agent bees" were re-identified in subsequent frames by the tracking procedure and triangulated into real-world coordinates. These algorithms were required to calculate the three spatial motion components (dx: horizontal, dy: vertical and dz: towards and from the comb) of individual bees over time.
  
  
  CONCLUSIONS
  The method enables the assessment of the 3D positions of individual Giant honeybees, which is not possible with single-view cameras. The method can be applied to distinguish at the individual bee level active movements of the thoraces produced by abdominal flipping from passive motions generated by the moving bee curtain. The data provide evidence that the z-deflections of thoraces are potential cues for colony-intrinsic communication. The method helps to understand the phenomenon of collective decision-making through mechanoceptive synchronization and to associate shimmering with the principles of wave propagation. With further, minor modifications, the method could be used to study aspects of other mass phenomena that involve active and passive movements of individual agents in densely packed clusters.
authors.affiliation: Institute of Zoology, University Graz, Graz, Austria. gerald.kastberger@uni-graz.at.
authors.forename: Gerald
authors.initials: G
authors.lastname: Kastberger
authors.forename: Michael
authors.initials: M
authors.lastname: Maurer
authors.forename: Frank
authors.initials: F
authors.lastname: Weihmann
authors.forename: Matthias
authors.initials: M
authors.lastname: Ruether
authors.forename: Thomas
authors.initials: T
authors.lastname: Hoetzl
authors.forename: Ilse
authors.initials: I
authors.lastname: Kranner
authors.forename: Horst
authors.initials: H
authors.lastname: Bischof