Data from: Escape distance in ground-nesting birds differs with individual level of camouflage

Camouflage is one of the most widespread antipredator strategies in the animal kingdom, yet no animal can match its background perfectly in a complex environment. Therefore, selection should favor individuals that use information on how effective their camouflage is in their immediate habitat when responding to an approaching threat. In a field study of African ground-nesting birds (plovers, coursers, and nightjars), we tested the hypothesis that individuals adaptively modulate their escape behavior in relation to their degree of background matching. We used digital imaging and models of predator vision to quantify differences in color, luminance, and pattern between eggs and their background, as well as the plumage of incubating adult nightjars. We found that plovers and coursers showed greater escape distances when their eggs were a poorer pattern match to the background. Nightjars sit on their eggs until a potential threat is nearby, and, correspondingly, they showed greater escape distances when the pattern and color match of the incubating adult's plumage-rather than its eggs-was a poorer match to the background. Finally, escape distances were shorter in the middle of the day, suggesting that escape behavior is mediated by both camouflage and thermoregulation.

伪装（camouflage）是动物界中分布最广泛的反捕食策略（antipredator strategy）之一，但在复杂环境中，没有任何动物能够完美匹配其所处背景。因此，自然选择应当更青睐那些在应对逼近的威胁时，能够利用自身伪装在当前生境中的有效性信息的个体。我们针对非洲陆筑巢鸟类（plovers, coursers, and nightjars）开展了野外实地研究，以此检验这一假说：个体可根据其与背景的匹配程度自适应调节逃逸行为。我们借助数字成像技术与捕食者视觉模型，量化了鸟卵与其所处背景之间，以及孵卵成年夜鹰的羽毛与背景之间在色彩、亮度与图案上的差异。研究结果显示，当鸻与走鸻的鸟卵与背景的图案匹配度较差时，其逃逸距离会更远。夜鹰会一直伏在鸟卵上直至潜在威胁临近，相应地，当孵卵成年夜鹰的羽毛（而非鸟卵）与背景的图案和色彩匹配度较差时，其逃逸距离会更远。最后，正午时分的逃逸距离更短，这表明逃逸行为同时受伪装与体温调节（thermoregulation）的共同调控。