ABSTRACT Gloger's rule is a classic ecogeographical principle that, in its simplest version, predicts animals should be darker in warmer and wetter climates. In a rarely tested more complex version, it also predicts animals should be more rufous in warmer and drier climates. The Variable Antshrike (Thamnophilus caerulescens) is a widely distributed South American passerine that presents an impressive amount of plumage color variation and occupies a wide variety of climatic conditions. Moreover, genetic and vocal evidence indicate ongoing hybridization in south-central Bolivia among 3 populations with very distinct plumages. We collected color data from 232 specimens from throughout this species' distribution to test the predictions of Gloger's rule. We found a negative correlation between brightness and precipitation, consistent with the simple version of Gloger's rule. In contrast, we found that birds were darker in cooler climates, contrary to the simple version of Gloger's rule, but consistent with recent findings in other taxa. We found support for both predictions of the complex Gloger's rule and suggest it might be driven by background matching. We conclude by concurring with a recent suggestion that the simple version of Gloger's rule should be reformulated exclusively in terms of humidity. LAY SUMMARY Almost 200 years ago, the German naturalist Constantin Gloger predicted that birds that live in warm and rainy areas tend to be darker than those that in live in cool and dry areas. He also predicted that birds tend to be browner when they live in dry areas. This pattern has come to be known as Gloger's rule. South America has the world's greatest bird diversity, but Gloger's rule has almost never been studied in South American birds. This is an important question to address because it can help us learn about how species evolve respond to their environments. It becomes even more important in our era of human-induced climatic changes. We studied Gloger's rule in the aptly named Variable Antshrike. This small South American bird species varies geographically in color from almost all black to almost all white. We used a technique called reflectance spectrophotometry, which allows us to precisely quantify the colors of feathers. We measured over 200 specimens kept in natural history collections. The majority of those specimens were collected by one of us (Brumfield) in Bolivia in the early 2000s. This is the largest sample size ever used to study Gloger's rule in a tropical bird. As predicted by Gloger, we found that the Variable Antshrike tends to be darker in rainier areas, and it tends to be browner in drier and warmer areas. But contrary to Gloger's ideas, we found that it tends to be darker in cooler, not warmer, areas. We suggest that this might be because being dark in cooler places helps birds maintain warm body temperatures. We also suggest that being brown in dry areas helps the birds camouflage amidst sparse vegetation.

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在可变蚁鵟（Thamnophilus caerulescens，Thamnophilidae）中测试Gloger规则的简单和复杂版本

摘要 Gloger 法则是一个经典的生态地理学原理，在其最简单的版本中，它预测动物在温暖和潮湿的气候中应该颜色更深。在一个很少测试的更复杂的版本中，它还预测动物在温暖和干燥的气候中应该更红润。变异蚁鸫（Thamnophilus caerulescens）是一种广泛分布的南美雀鸟，呈现出令人印象深刻的羽毛颜色变化，并适应各种气候条件。此外，遗传和声音证据表明，玻利维亚中南部 3 个羽毛非常不同的种群正在进行杂交。我们从整个物种分布的 232 个标本中收集了颜色数据，以测试 Gloger 规则的预测。我们发现亮度和降水量呈负相关，与格洛格规则的简单版本一致。相比之下，我们发现鸟类在较冷的气候中颜色更深，这与 Gloger 规则的简单版本相反，但与最近在其他分类群中的发现一致。我们发现了对复杂 Gloger 规则的两种预测的支持，并认为它可能是由背景匹配驱动的。最后，我们同意最近的一个建议，即 Gloger 规则的简单版本应该完全根据湿度重新制定。概述 大约 200 年前，德国博物学家康斯坦丁·格洛格 (Constantin Gloger) 预测，生活在温暖多雨地区的鸟类往往比生活在凉爽干燥地区的鸟类颜色更深。他还预测，当鸟类生活在干燥地区时，它们往往会变得更棕色。这种模式后来被称为 Gloger 规则。南美洲拥有世界上最大的鸟类多样性，但几乎从未在南美洲鸟类中研究过 Gloger 的规则。这是一个需要解决的重要问题，因为它可以帮助我们了解物种进化如何对其环境做出反应。在我们这个人为引起气候变化的时代，它变得更加重要。我们在恰如其分的 Variable Antshrike 中研究了 Gloger 的规则。这种南美小型鸟类的颜色在地理上各不相同，从几乎全黑到几乎全白。我们使用了一种称为反射分光光度法的技术，它使我们能够精确量化羽毛的颜色。我们测量了保存在自然历史收藏中的 200 多个标本。这些标本中的大部分是在 2000 年代初由我们中的一个人（布鲁姆菲尔德）在玻利维亚收集的。这是有史以来用于研究热带鸟类格洛杰法则的最大样本量。正如 Gloger 预测的那样，我们发现可变蚁鸫在雨量较多的地区往往颜色较深，而在较干燥和较温暖的地区，它往往颜色较深。但与 Gloger 的想法相反，我们发现在较冷而非较暖的地区，它往往更暗。我们认为这可能是因为在较冷的地方保持黑暗有助于鸟类保持温暖的体温。我们还建议在干燥地区呈棕色有助于鸟类在稀疏植被中伪装。我们认为这可能是因为在较冷的地方保持黑暗有助于鸟类保持温暖的体温。我们还建议在干燥地区呈棕色有助于鸟类在稀疏植被中伪装。我们认为这可能是因为在较冷的地方保持黑暗有助于鸟类保持温暖的体温。我们还建议在干燥地区呈棕色有助于鸟类在稀疏植被中伪装。