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.
The ability to recognize and evaluate others is considered to be an important ability in selecting cooperative partners. There have been some studies on this ability in both humans and nonhuman animals, however, little empirical research has been conducted to examine how horses perceive humans. Here, we investigated whether horses can evaluate the problem-solving ability of humans in an unsolvable task. We showed horses a pair of two experimenters, one who can open the lid of a container (problem solver) and the other who cannot open the lid of the container (problem nonsolver), trying to open the lid of the container either with or without food in it. Gaze duration toward each experimenter was recorded and used as a proxy measurement of the attention of the horses. Horses watched the problem solver longer than the problem nonsolver in the food condition. They also watched the problem solver for longer in the food condition compared to the no food condition. These results suggest that horses can recognize the problem-solving ability of humans.
There has been much research into the ability of large-billed crows (Corvus macrorynchos) to recognize pictures, but little is known about what cues in a picture they use for recognition. We trained four adult crows to select pictures of specific species of bird, and we examined the effects of picture modification on their selections. Two of them were trained to select pictures of sparrow from other species of birds in a two-alternative forced choice test; the other two were trained to select pictures of pigeon. After selecting the 'correct' bird, they were tasked to select novel and modified pictures. We found that the crows' discrimination was greatly affected by the color of the image, but that they could not select the correct image only from its colors; they also used features such as shapes and patterns to select the correct image. In addition, we found that the cues used to recognize the pictures may have differed between individuals.