Biology textbooks describe the small changes in the beaks of the Galápagos finches as exemplars of how birds evolve in response to environmental changes. However, recent studies of the abundant fossil birds at Rancho La Brea find no evidence of evolutionary responses to the dramatic climate changes of the glacial–interglacial cycle over the past 35 000 years: none of the large birds exhibit any change in body size or limb proportions, even during the last glacial maximum approximately 18 000–20 000 years ago, when the southern California chaparral was replaced by snowy coniferous forests. However, these are all large birds with large ranges and broad habitat preferences, capable of living in many different environments. Perhaps the smaller birds at La Brea, which have smaller home ranges and narrower habitats, might respond to climate more like Galápagos finches. The only 3 common small birds at La Brea are the western meadowlark, the yellow‐billed magpie and the raven. In this study, we demonstrate that these birds also show complete stasis over the last glacial–interglacial cycle, with no statistically significant changes between dated pits. Recent research suggests that the small‐scale changes over short timescales seen in the Galápagos finches are merely fluctuations around a stable morphology, and rarely lead to long‐term accumulation of changes or speciation. Instead, the prevalence of stasis supports the view that long‐term directional changes in morphology are quite rare. While directional changes in morphology occur frequently over short (<1 ka) timescales, in the long term such changes only rarely remain stable for long enough to appear in the fossil record.

中文翻译：

---

小型鸟类如何响应气候变化而进化？来自La Brea焦油坑的长期记录的数据。

生物学教科书将加拉帕戈斯雀的喙的微小变化描述为鸟类如何响应环境变化而进化的典范。但是，最近对兰乔拉布雷亚（Rancho La Brea）丰富的化石鸟类的研究发现，没有证据表明在过去35000年中，冰川-冰川间周期发生了剧烈的气候变化，而没有进化反应：所有大型鸟类都没有身体或肢体的任何变化甚至在大约18 000-20 000年前的最后一次冰川最大时期，南加州丛林被白雪的针叶林所取代。然而，这些都是大型鸟类，具有广泛的范围和广泛的栖息地偏好，能够生活在许多不同的环境中。也许拉布雷亚（La Brea）的小鸟，它们的家禽范围较小，栖息地较窄，可能对气候的反应更像加拉帕戈斯雀。拉布雷亚（La Brea）仅有的3只普通小鸟是西部的草地雀，黄嘴喜and和乌鸦。在这项研究中，我们证明了这些鸟类在最后一个冰期至冰间期循环中也显示出完全的停滞状态，在过时的凹坑之间没有统计学上的显着变化。最近的研究表明，在加拉帕戈斯雀科中观察到的短时间内的小规模变化仅仅是围绕稳定形态的波动，很少导致变化或物种的长期积累。取而代之的是，瘀血的流行支持了这样一种观点，即形态学的长期方向变化非常罕见。虽然形态的方向变化经常在短（<1 ka）的时间范围内发生，