Data from: Optimizing countershading camouflage

Because the sun and sky are above us, natural illumination is directional and the cues from shading reveal shape and depth. However, many animals are darker on their backs and, over 100 years ago, it was proposed that this phenomenon was camouflage: countering the cues to shape that directional illumination creates. However, does this camouflage work in practice? We predicted the optimal countershading for different lighting conditions and tested this possibility with correspondingly patterned model “caterpillars” predated by birds in the wild. Predation rates varied with coloration and lighting in exactly the manner predicted. Such subtlety in the effects of countershading vindicates conclusions from prior evidence demonstrating stronger countershading in animals in more brightly lit habitats.由于太阳与天穹高悬于我们上方，自然光照具有方向性，阴影所传递的视觉线索可揭示物体的形状与深度。然而，诸多动物的背部体色更深；早在一百余年前，便有学者提出此种反荫蔽（countershading）现象属于伪装策略——通过抵消定向光照所产生的形状感知线索，以此实现伪装效果。然而，这种伪装策略在实际环境中是否奏效？为此，我们针对不同光照条件预测了最优反荫蔽体色方案，并借助野外被鸟类捕食的对应花纹模型“毛虫”开展了验证实验。捕食率随体色与光照条件的变化规律与我们的预测完全一致。反荫蔽效应所具备的此种精妙性，佐证了此前研究证据所得出的结论：栖息于光照更充足生境中的动物，其反荫蔽体色往往更为显著。