Effective conservation planning for species of concern requires long-term monitoring data that can accurately estimate population trends. Supplemental or alternative methods for estimating population trends are necessary for species that are poorly sampled by traditional breeding bird survey methods. Counts of migrating birds are commonly used to assess raptor population trends and could be useful for additional taxa that migrate diurnally and are difficult to monitor during the breeding season. In North America, the Common Nighthawk (Chordeiles minor) is challenging to detect during comprehensive dawn surveys like the North American Breeding Bird Survey and is considered a species of conservation concern because of steep population declines across its range. We conducted standardized evening counts of migrating Common Nighthawks at a fixed survey location along western Lake Superior each autumn from 2008 to 2022. To document peak migration activity, counts spanned ~3 hours each evening from mid-August to early September for a mean of 19.4 ± 2.4 days. These count data were then used to assess the effects of weather on daily counts and high-count days and to calculate population trends over this 15-year period. We used generalized linear mixed effects models to determine the relationship between daily counts and high-count days (i.e., ≥1000 migrating nighthawks) and weather variables. Additionally, using our 15-year dataset, we calculated a geometric mean passage rate that accounted for annual differences in weather to estimate count trends. Annual counts averaged ~18,000 (min = 2514, max = 32,837) individuals and high-count days occurred 56 times throughout the course of the study. Model results indicated lighter, westerly winds and warmer temperatures were associated with higher daily counts and greater probability of a large migratory flight. Results from the trend analyses suggest stable or non-significantly increasing trends for Common Nighthawks during this monitoring period; however, the trend models explained a relatively low percentage of the variation in the counts. Results from a power analysis suggest that continued monitoring efforts and adjustments with weather covariates will be necessary to effectively use visible migration count data to estimate Common Nighthawk trends. Establishing annual monitoring programs that use standardized visual counts to document Common Nighthawk migration at key sites across North America may provide supplemental information useful for population trend estimates of this species. Therefore, we advocate for the use of visible migration counts to monitor Common Nighthawks in North America and emphasize the value of long-term monitoring efforts.

The post Incorporating weather in counts and trends of migrating Common Nighthawks first appeared on Avian Conservation and Ecology.

对受关注物种的有效保护规划需要能够准确估计种群趋势的长期监测数据。对于传统种鸟调查方法采样效果较差的物种，有必要采用补充或替代方法来估计种群趋势。迁徙鸟类的计数通常用于评估猛禽种群趋势，并且对于每日迁徙且在繁殖季节难以监测的其他类群可能有用。在北美，普通夜鹰（Chordeilesminor）在像北美繁殖鸟类调查这样的全面黎明调查中很难被发现，并且由于其分布范围内的种群数量急剧下降而被认为是一个受保护的物种。从 2008 年到 2022 年，我们每年秋天都会在苏必利尔湖西部的一个固定调查地点对夜间迁徙的夜鹰进行标准化计数。为了记录迁徙活动高峰期，从 8 月中旬到 9 月初，每个晚上的计数时间约为 3 小时，平均值为 19.4 ± 2.4 天。然后使用这些计数数据来评估天气对每日计数和高计数天数的影响，并计算这 15 年期间的人口趋势。我们使用广义线性混合效应模型来确定每日计数和高计数天数（即，≥1000 只迁徙的夜鹰）与天气变量之间的关系。此外，利用我们 15 年的数据集，我们计算了几何平均通过率，该比率考虑了每年的天气差异，以估计计数趋势。年度计数平均约为 18,000 人（最小值 = 2514，最大值 = 32,837），在整个研究过程中，高计数日出现 56 次。模型结果表明，较轻的西风和较温暖的气温与较高的日计数和较大的大规模迁徙飞行的可能性有关。趋势分析结果表明，在此监测期间，普通夜鹰的趋势稳定或非显着增加；然而，趋势模型解释的计数变化的百分比相对较低。功率分析的结果表明，为了有效地使用可见的迁徙计数数据来估计常见夜鹰趋势，需要继续监测工作并根据天气协变量进行调整。建立年度监测计划，使用标准化目视计数来记录北美关键地点的普通夜鹰迁徙，可能会为该物种的种群趋势估计提供有用的补充信息。因此，我们主张使用可见的迁徙计数来监测北美的普通夜鹰，并强调长期监测工作的价值。

将天气纳入迁徙的普通夜鹰的数量和趋势的帖子首次出现在鸟类保护和生态学上。