Distance-dependent defensive coloration

spatial frequencies (as projected onto the retina) and these will dominate perceptual grouping mechanisms. With increasing distance, the highest frequencies are lost, and the components of the visual scene to which the viewer is most sensitive change systematically [10]. The multi-scale processing of images has been exploited to create hybrid pictures that vary with distance in, for example, perceived identity [7] (Figure 1A). In nature, manipulation of pattern elements potentially allows for control over which features are visible from which distance. We tested whether a distance-dependent pattern displaying (low spatial frequency) camouflage when viewed from a distance and (high spatial frequency) aversive stripes when close can confer survival benefits over either alone. In experiments 1, 3 and 4, we presented paper moth-like targets pinned to tree bark, and baited with dead mealworms, to free-living avian predators (Supplemental information). In experiment 1, we used targets designed to have aversive coloration (yellow-and-black stripes, a typical aposematic color, although it does not actually matter if the aversion is via another mechanism, such as neophobia), background matching camouflage and a distance-dependent dual-function pattern exhibiting camouflage from a distance but revealing aversive stripes when close (Figure 1B). This dual-function pattern was created using a Fourier transform to combine the high frequency yellow-and-black stripes with the spatial frequencies of background matching camouflage lower than those in the aversive pattern. Additional treatments controlled for the removal of high frequency information from the camouflaged pattern, the addition of stripes per se, and the role of low frequency patterning with a plain average color reference. We found a significant effect of treatment (W=38.81, d.f.=5, p<0.001) and block (W=114.63, d.f.=12, p<0.001). There was significantly higher survival of the distance-dependent dual-function pattern when compared to background matching camouflage (a-e: z=-4.606, d.f.=1, p<0.001) and the aposematic pattern alone (d-e: z=-2.82, d.f.=1, p=0.005) (Figure 1C). Crucially, there was no effect of removing the high frequency information from background matching Camouflage and warning coloration are usually viewed as alternative defensive strategies at opposite ends of the conspicuousness continuum. However, camouflage is compromised by factors such as habitat heterogeneity and motion [1], and aposematism bears the cost of ineffectiveness against ignorant, hasty or nutritionally stressed predators [2]. To reduce these costs, it has been suggested that camouflage and warning coloration can be combined by the use of patterns that are detectable at different distances [3]. This hypothesis finds support in experiments on humans searching for …