North American grassland birds colonized emerging habitat created by expanding agriculture in a pattern of eastward expansions from the mid-1800s to mid-1900s. These birds have been declining, since at least the mid-1900s, largely as result of anthropogenic landscape change. Only one bird that now breeds predominantly in southeastern pine savannas is thought to have experienced a concurrent range expansion into this region: Peucaea aestivalis (Bachman’s Sparrow). However, our understanding of the P. aestivalis expansion, and subsequent retraction to the southeastern United States, is largely based on a contemporaneous review of only a subset of historical records from beyond its modern, northern limit. We suggest an alternative explanation for these historical records is that P. aestivalis historically occurred more broadly than was recognized in contemporaneous literature. To evaluate these hypotheses, we reviewed field observations from literature, natural history collections, and eBird to show how P. aestivalis presence throughout eastern North America has shifted since the mid-1800s. To confirm that these findings were not the result of detection bias, we repeated our analysis on a common sparrow species (Spizella pusilla) with a largely overlapping breeding range, but no history of expansion and retraction. We confirm that P. aestivalis expanded its range, but add that prior to that expansion, its historical distribution was broader than commonly acknowledged today. As a result, we identify the northwestern historical limit of P. aestivalis, the Ouachita and Ozark highlands, as a potential source region for an eastward expansion that is consistent with those of other North American grassland birds of the era. We discuss the potential evolutionary and conservation implications of this range expansion on P. aestivalis given our more nuanced understanding of it. Anthropogenic landscape change initially provided additional habitat for P. aestivalis but has ultimately resulted in a reduction of the P. aestivalis distribution.

中文翻译：

---

自然历史和社区科学记录证实了自 1850 年以来巴赫曼麻雀 (Peucaea aestivalis) 分布的快速地理变化

北美草原鸟类在 1800 年代中期至 1900 年代中期以向东扩张的模式扩展农业而形成的新兴栖息地定居。至少自 1900 年代中期以来，这些鸟类一直在减少，这主要是由于人为景观变化的结果。现在只有一种主要在东南松树稀树草原繁殖的鸟类被认为同时经历了向该地区扩张的范围：Peucaea aestivalis（巴赫曼麻雀）。然而，我们对 P. aestivalis 扩张的理解，以及随后撤回到美国东南部的理解，主要是基于对其现代北部界限之外的历史记录的一个子集的同期回顾。我们建议对这些历史记录的另一种解释是 P. aestivalis 历史上发生的范围比同时代文献中所承认的要广泛。为了评估这些假设，我们回顾了来自文献、自然历史收藏和 eBird 的实地观察，以展示自 1800 年代中期以来，北美东部的 P. aestivalis 如何发生变化。为了证实这些发现不是检测偏差的结果，我们重复了我们对一种常见的麻雀物种（Spizella pusilla）的分析，该物种的繁殖范围有很大重叠，但没有扩张和收缩的历史。我们确认 P. aestivalis 扩大了它的范围，但补充说，在扩大之前，它的历史分布比今天普遍承认的要广泛。因此，我们确定了 P. aestivalis、Ouachita 和 Ozark 高地的西北历史界限，作为与那个时代其他北美草原鸟类一致的向东扩张的潜在来源地区。鉴于我们对它的更细致的理解，我们讨论了这种范围扩展对 P. aestivalis 的潜在进化和保护意义。人为景观变化最初为 P. aestivalis 提供了额外的栖息地，但最终导致 P. aestivalis 分布的减少。