Physics & Astronomy Department, Haverford College, Haverford, Pennsylvania, United States of America.
Migratory Bird Center, Smithsonian Conservation Biology Institute, National Zoological Park, Washington DC, United States of America.
PLoS One. 2019 Apr 24;14(4):e0210924. doi: 10.1371/journal.pone.0210924. eCollection 2019.
Colorful feathers have long been assumed to be conspicuous to predators, and hence likely to incur costs due to enhanced predation risk. However, many mammals that prey on birds have dichromatic visual systems with only two types of color-sensitive visual receptors, rather than the three and four photoreceptors characteristic of humans and most birds, respectively. Here, we use a combination of multispectral imaging, reflectance spectroscopy, color vision modelling and visual texture analysis to compare the visual signals available to conspecifics and to mammalian predators from multicolored feathers from the Indian peacock (Pavo cristatus), as well as red and yellow parrot feathers. We also model the effects of distance-dependent blurring due to visual acuity. When viewed by birds against green vegetation, most of the feathers studied are estimated to have color and brightness contrasts similar to values previously found for ripe fruit. On the other hand, for dichromat mammalian predators, visual contrasts for these feathers were only weakly detectable and often below detection thresholds for typical viewing distances. We also show that for dichromat mammal vision models, the peacock's train has below-detection threshold color and brightness contrasts and visual textures that match various foliage backgrounds. These findings are consistent with many feathers of similar hue to those studied here being inconspicuous, and in some cases potentially cryptic, in the eyes of common mammalian predators of adult birds. Given that birds perform many conspicuous motions and behaviors, this study suggests that mammalian predators are more likely to use other sensory modalities (e.g., motion detection, hearing, and olfaction), rather than color vision, to detect avian prey. This suggests new directions for future behavioral studies and emphasizes the importance of understanding the influence of the sensory ecology of predators in the evolution of animal coloration.
彩色羽毛长期以来被认为对捕食者具有明显的警示作用，因此很可能由于增加了被捕食的风险而带来代价。然而，许多以鸟类为食的哺乳动物具有双色视觉系统，只有两种类型的色觉感光受体，而不是人类和大多数鸟类分别具有的三种和四种光感受器。在这里，我们使用多光谱成像、反射光谱学、颜色视觉建模和视觉纹理分析相结合的方法，比较了来自印度孔雀（Pavo cristatus）以及红色和黄色鹦鹉羽毛的多色羽毛的同类和哺乳动物捕食者可以看到的视觉信号。我们还模拟了由于视觉敏锐度导致的距离相关模糊的影响。当鸟类在绿色植被中观察这些羽毛时，研究中大多数羽毛的颜色和亮度对比度估计与之前为成熟水果发现的值相似。另一方面，对于二色视的哺乳动物捕食者来说，这些羽毛的视觉对比度只有微弱的可检测性，而且通常低于典型观察距离的检测阈值。我们还表明，对于二色视哺乳动物视觉模型，孔雀的尾屏具有低于检测阈值的颜色和亮度对比度以及与各种树叶背景相匹配的视觉纹理。这些发现与许多与本文研究的羽毛具有相似色调的羽毛在常见的成年鸟类的哺乳动物捕食者眼中不显眼的情况一致，在某些情况下甚至可能是隐蔽的。鉴于鸟类表现出许多显眼的动作和行为，本研究表明，哺乳动物捕食者更有可能使用其他感觉模态（例如运动检测、听觉和嗅觉），而不是颜色视觉，来检测鸟类猎物。这为未来的行为研究提供了新的方向，并强调了了解捕食者的感觉生态学对动物颜色进化的影响的重要性。
