View from below: experimental manipulation of water surfaces to evaluate visual integrity of heron-like models through Snell's window.

This article investigates how varying water surface conditions affect the visual integrity of above-surface predator models as seen from below through Snell's window, a 97° optical cone created by light refraction at the water–air interface. Using experimental manipulations of flat surfaces, smooth waves, and different levels of current-induced turbulence, the study found that increased surface disturbance causes progressive fragmentation and distortion of predator profiles, with smooth waves producing horizontal banding and currents causing extensive fragmentation. These visual effects resemble natural frontal plumage patterns in some wading birds (Ardeidae) and shorebirds (Charadriiformes), suggesting that such plumage may have evolved as an adaptation to foraging through the water–air interface by reducing detectability to subsurface prey. The findings highlight a complex interaction between water surface conditions, predator-prey visual dynamics, and potential evolutionary influences on avian plumage patterns in shoreline habitats.