Viewing geometry and pattern type shape the detectability of snakes

Abstract

Protective coloration can reduce predation risk by altering how prey are detected, recognised, or attacked. High-contrast markings may function as warning signals, camouflage, or both. In snakes, dorsal colour patterns are highly variable but the function remains debated, particularly because their appearance to an observer may change with viewing distance and angle. This study tested whether the function and efficacy of common snake pattern types (blotches, spots, diamonds, zig-zags and bands) is observer-view dependent, mediated by viewing distance and angle. Artificial snake models marked with these different pattern types that are broadly common across snake taxa, were placed in woodland habitat with a mixed shrub and grass understorey in Cornwall, UK, with photographs taken for evaluating levels of predicted camouflage and contrast against the background. Next, human volunteers searched for models, and we recorded detection distances and angles. Field results showed no significant difference in overall detection rates between pattern types; however, zigzag-patterned models were more likely to be detected at significantly shorter distances than blotch-patterned models, with a marginal trend towards shorter distances than diamond-patterned models, indicating effective longer-range camouflage. Detection risk did not alter gradually as volunteers approached but increased abruptly, correlating with image analyses showing that levels of predicted disruptive camouflage decreased with reduced distance. When detection was analysed using viewing angle, an advantage of zigzag patterns was robust to geometric scale, and observer height may further shape detection through viewing geometry. These findings suggest that snake dorsal patterns could potentially serve dual roles in reducing detection from afar, while being more conspicuous at close range. In addition, the results highlight the need to consider three-dimensional viewing geometry, including distance and visual angle, when evaluating the ecological function of animal coloration.