Effects of eye cap occlusion on visual distance and fixating duration of pecking in pigeons

Avian pecking behavior in birds, analogous to reach-to-grasp in primates, is accompanied by unstable vision due to the co-location of the eyes and bills on the head. Fixation in birds, a brief pause during pecking, enables them to stabilize their visual input to plan their further movements. Several bird species have two high-acuity retinal regions, the area dorsalis and the fovea centralis, which receive input from frontal and lateral visual fields, respectively. However, the contributions of these regions to natural pecking during fixation, especially temporal dynamics and head posture involved in accommodation, remain poorly understood. We assessed the effects of visual-field-specific occlusion on the fixation behavior of pigeons, provided with three types of eye caps: frontal occlusion, lateral occlusion, and a no-occlusion control. Using video tracking methods, we analyzed the visual distance toward the target, fixation duration, head depression angle, and the covariation between visual distance and duration. Frontal occlusion markedly prolonged fixation duration and increased the head depression angle, whereas visual distance remained unaffected across conditions. Furthermore, the covariation between visual distance and fixation duration under control condition was abolished under frontal occlusion. These results suggest that the role of frontal vision involves the area dorsalis in temporal and postural compensation for accommodation during fixation of pecking.