Vision and Foraging in Structurally Complex Habitats: Common Moorhens (Gallinula chloropus) See the Way Ahead.

This study quantifies the visual field configuration of common moorhens (Gallinula chloropus) to examine how sensory systems balance the competing demands of foraging and predator detection in structurally complex habitats. Using the ophthalmoscopic reflex method, we show that moorhens possess a vertically elongated but relatively narrow binocular field (maximum width ~34°, vertical extent 125°), coupled with extensive monocular coverage producing a near-panoramic cyclopean field (~300°). This configuration aligns with patterns observed in visually guided foragers and is consistent with a role in precise bill control during close-range feeding, while maintaining wide lateral and posterior coverage for predator detection. Visual access to the substrate is posture-dependent, requiring head pitching during foraging, indicating dynamic modulation of sensory input. Comparisons with blue cranes (Grus paradisea) highlight ecological, rather than phylogenetic, drivers of visual field variation. These findings provide novel baseline data for Rallidae and reinforce the role of sensory trade-offs in shaping avian ecological performance.