"Corvid Tracking Studio" : A custom-built motion capture system to track head movements of corvids

Abstract

Recent technological advances made it possible to record postural changes of moving animals in behavior/cognition research. Although several technologies are available for this purpose, one underexplored possibility is the use of an infrared motion-capture system, which excels at tracking subtle and rapid 3D movements of animals. We explored this possibility by developing a system optimized to track saccadic head movements of large-billed crows (Corvus macrorhynchos). We custom-built a motion-capture room, "Corvid Tracking Studio", in which birds can freely interact with conspecifics/objects while infrared cameras track the reflective markers attached to the birds' heads. We also developed a head-calibration method that reconstructs the 3D positions of each bird's eyes and beak tip with respect to those of the head markers. We then tested accuracies of the head-orientation coordinate system reconstructed from the eye-beak coordinates of a bird and confirmed that estimated errors were all within a degree (in Euler angles). We thus show that a motion capture system has a good potential to examine subtle and rapid movements of moving animals with several customizations.