Data from: Camouflaging moving objects: crypsis and masquerade

Motion is generally assumed to ‘break’ camouflage. However, although camouflage cannot conceal a group of moving animals, it may impair a predator’s ability to single one out for attack, even if that discrimination is not based on a color difference. Here we use a computer-based task in which humans had to detect the odd one out among moving objects, with ‘oddity’ based on shape. All objects were either patterned or plain, and either matched the background or not. We show that there are advantages of matching both group-mates and the background. However, when patterned objects are on a plain background (i.e. no background matching), the advantage of being among similarly patterned distractors is only realized when the group size is larger (ten compared to five). In a second experiment we present a paradigm for testing how coloration interferes with target-distractor discrimination, based on an adaptive staircase procedure for establishing the threshold. We show that when the predator only has a short time for decision-making, displaying a similar pattern to the distractors and the background affords protection even when the difference in shape between target and distractors is large. We conclude that, even though motion breaks camouflage, being camouflaged could help group-living animals reduce the risk of being singled out for attack by predators.

学界普遍认为运动可‘打破’伪装（camouflage）。然而，尽管伪装无法隐藏一整群移动的动物，但它仍可能削弱捕食者单独挑出个体进行攻击的能力——即便这种甄别并非基于色彩差异。本研究采用基于计算机的实验范式，要求人类受试者在移动物体中甄别出形状特异的个体。所有物体均分为有纹理与无纹理两类，同时又可分为与背景匹配或不匹配两类。研究结果表明，同时与同类群成员及背景保持外观匹配具有生存优势。但当有纹理的物体置于无纹理背景（即不与背景匹配）时，身处同类纹理干扰物中的优势仅在群体规模较大（10个个体相较于5个个体）时才会显现。在第二项实验中，我们基于用于确定阈值的自适应阶梯法，提出了一种测试色彩如何干扰目标-干扰物甄别能力的实验范式。研究发现，当捕食者仅拥有较短决策时间时，即便目标与干扰物的形状差异显著，只要个体外观与干扰物及背景保持一致，即可获得防护效果。综上，尽管运动可打破伪装，但具备伪装能力仍可帮助群居动物降低被捕食者单独挑出攻击的风险。