Billions of birds annually migrate between breeding and nonbreeding grounds in North America. During fall 2020, there was a series of alarming mass-mortality events of migratory birds across the western United States, with estimates of 100,000 to 1 million birds having perished. One potential culprit behind these die-offs is wildfires, though there has been little research documenting the indirect effects of wildfires on actively migrating birds. We undertook a multi-year assessment of potential impacts that wildfires may have had on fall bird migration over the past decade, with a particular focus on fall 2020, using systematic bird banding data from southeastern Utah. We used a correlative approach to evaluate the relationship between estimates of acres burned by wildfires in western North America on several variables representing bird abundance and body condition. Notably, in our best fit models of birds banded at our research site during fall 2020, we found both a positive relationship for the number of bird captures and a negative relationship for body mass index with more daily burned acres. We provide an examination of incorporating lag effects of wildfires on different metrics of bird migration to account for potential impacts of fires on birds before migration and banding. Additionally, we assess the usefulness of different proxies of body condition in highly stressed land birds and introduce a scale for scoring emaciation of birds in the hand while banding. Our insights into avian migration ecology are one of the few studies that explore the role wildfires may have had in affecting migratory bird movements and health.

中文翻译：

---

野火活动加剧期间北美西部的秋季鸟类迁徙

每年有数十亿只鸟类在北美的繁殖地和非繁殖地之间迁徙。2020 年秋季，美国西部发生了一系列令人震惊的候鸟大规模死亡事件，估计有 10 万至 100 万只候鸟死亡。这些死亡背后的一个潜在罪魁祸首是野火，尽管很少有研究记录野火对活跃的迁徙鸟类的间接影响。我们使用来自犹他州东南部的系统鸟类标记数据，对过去十年野火可能对秋季鸟类迁徙产生的潜在影响进行了多年评估，特别关注 2020 年秋季。我们使用相关方法来评估北美西部被野火烧毁的英亩数与代表鸟类数量和身体状况的几个变量之间的关系。值得注意的是，在我们 2020 年秋季期间在我们研究地点捆扎的鸟类的最佳拟合模型中，我们发现鸟类捕获数量呈正相关，体重指数与每日燃烧面积增加呈负相关。我们提供了一项关于野火对鸟类迁徙不同指标的综合滞后效应的检查，以解释火灾对迁徙和分界前鸟类的潜在影响。此外，我们评估了不同身体状况代理指标在高度紧张的陆地鸟类中的实用性，并引入了一个评分量表，用于在绑带时对鸟类的手部消瘦进行评分。