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

Abstract

Abstract The water–air interface is a globally widespread habitat for interactions between prey and predators. We experimentally manipulated water surface conditions (flat, smooth waves, three levels of current-induced turbulence) and digitally quantified the visual integrity of above-surface models from a subsurface perspective. Progressive fragmentation was present in each of the models (upright heron, crouched heron, vertical block, horizontal block) with increased departure from flat surface conditions. Smooth directional waves produced multiple horizontal bands (shadows) that moved across the models while surface currents distorted the profile, including progressive disintegration of the models appearance into multiple fragments of different sizes. This fragmentation is caused by scattered surface irregularities interacting with waves and is accentuated at the broken periphery of the optical window, reducing recognition of the models. Unexpectedly, we found that bands and fragments emerging from different surface conditions resemble common frontal plumage patterns on some Ardeidae and shorebirds (Charadriiformes). While these natural plumages are widely recognized to reflect a diversity of adaptations, including camouflage in terrestrial habitats, we suggest that their resemblance to water surface-induced fragmentation might also reflect foraging adaptations of predators though the water–air interface.