Much of the biology of Black Swifts (Cypseloides niger) is poorly known due to the species’ mostly aerial existence and cryptic nesting habitat. Important aspects of the biology of the northern subspecies of Black Swift (C. n. borealis) have been described in the past two decades, but the difficulty in locating and accessing Black Swift breeding sites constrains a range-wide understanding of the species’ biology and abundance, and ultimately, the cause(s) of its population decline. The most widely used method to determine Black Swift breeding site occupancy is to monitor suitable nesting habitat during the last hours of daylight (evening surveys) to detect the presence of adults attending nests (i.e., flying to or from a cliff face). Potentially, dawn surveys could result in more detections if adults reliably leave their nests or roost sites at first light, after overnight attendance. Because the effectiveness of occupancy surveys has not been quantified, we compared detection rates between evening surveys and surveys in the first hours of daylight (dawn surveys) at nine known breeding sites in southern British Columbia in 2018. Next, we measured how detections varied over the dawn period at eight active breeding sites surveyed between 2018–2020 and seven breeding sites surveyed in August 2020 in southern British Columbia and western Alberta. At low light levels, 5.38 times the number of birds/minute were detected, on average, during dawn surveys, compared with evening surveys, with dawn to evening detection ratios as high as 8.93 at some sites. During dawn surveys, detections peaked 8 to 9 min before sunrise and declined rapidly as light levels increased after sunrise. We suggest using dawn surveys to determine breeding site occupancy and prioritize areas for nest searches, monitoring, and habitat protection to ultimately aid in conserving Black Swifts.

The post Optimizing survey timing for detecting a declining aerial insectivore, the Black Swift (Cypseloides niger borealis ) first appeared on Avian Conservation and Ecology.

由于黑雨燕（ Cypseloides niger ）主要在空中生存且筑巢栖息地神秘，因此人们对黑雨燕的大部分生物学知之甚少。黑雨燕 ( C. n. borealis)北方亚种生物学的重要方面）在过去的二十年中已经被描述过，但是定位和进入黑雨燕繁殖地的困难限制了对该物种的生物学和丰度的广泛了解，并最终限制了其种群数量下降的原因。确定黑雨燕繁殖地占用情况最广泛使用的方法是在白天的最后几个小时内监测合适的筑巢栖息地（夜间调查），以检测是否有成年雨燕进入巢穴（即飞向或飞离悬崖面）。如果成虫在过夜后能够在黎明时分离开巢穴或栖息地，那么黎明调查可能会导致更多的检测。由于入住率调查的有效性尚未量化，我们比较了 2018 年不列颠哥伦比亚省南部 9 个已知繁殖地的夜间调查和黎明调查（黎明调查）之间的检测率。接下来，我们测量了 2018 年期间调查的 8 个活跃繁殖地在黎明期间的检测变化。 –2020 年，并于 2020 年 8 月对不列颠哥伦比亚省南部和艾伯塔省西部的七个繁殖地进行了调查。在弱光条件下，黎明调查平均每分钟检测到的鸟类数量是夜间调查的 5.38 倍，某些地点黎明与傍晚的检测比率高达 8.93。在黎明调查期间，检测结果在日出前 8 至 9 分钟达到峰值，并随着日出后光照水平的增加而迅速下降。我们建议使用黎明调查来确定繁殖地点的占用情况，并优先考虑巢穴搜索、监测、

优化调查时间以检测日益减少的空中食虫动物黑雨燕 (Cypseloides niger borealis) 的帖子首次出现在《鸟类保护与生态学》上。