Abstract

Millions of wetland basins, embedded in croplands and grasslands, are biodiversity hotspots in North America’s Prairie Pothole Region, but prairie wetlands continue to be degraded and drained, primarily for agricultural activities. Aerial insectivorous swallows are known to forage over water, but it is unclear whether swallows exhibit greater selection for wetlands relative to other habitats in croplands and grasslands. Central-place foraging theory suggests that habitat selectivity should increase with traveling distance from a central place, such that foragers compensate for traveling costs by selecting more profitable foraging habitat. Using global positioning system (GPS) tags, we evaluated habitat selection by female Tree Swallows (Tachycineta bicolor) at 4 sites containing wetlands and where terrestrial land cover was dominated by grasslands (grass, herbaceous cover) and/or cultivated cropland. We also used sweep-net transects to assess the abundance and biomass of flying insects in different habitats available to swallows (wetland pond margins, grassy field margins, and representative uplands). As expected for a central-place forager, GPS-tagged swallows selected more for wetland ponds (disproportionate to availability), and appeared to increasingly select for wetlands with increasing distance from their nests. On cropland-dominated sites, insect abundance and biomass tended to be higher in pond margins or grassy field margins compared to cropped uplands, while abundance and biomass were more uniform among sampled habitats at sites dominated by grass and herbaceous cover. Swallow habitat selection was not clearly explained by the distribution of sampled insects among habitats; however, traditional terrestrial sampling methods may not adequately reflect prey distribution and availability to aerially foraging swallows. Overall, our results underscore the importance of protecting and enhancing prairie wetlands and other non-crop habitats in agricultural landscapes, given their disproportionate use and capacity to support breeding swallow and insect populations.

中文翻译：

---

中心地觅食理论预测农业景观湿地的树燕选择

摘要

埋在农田和草原中的数以百万计的湿地盆地是北美草原坑洼地区的生物多样性热点，但是草原湿地仍在退化和排水，主要用于农业活动。众所周知，空中食虫性燕子可以在水上觅食，但是相对于农田和草原上的其他栖息地，燕子是否对湿地表现出更大的选择尚不清楚。中心地觅食理论表明，栖息地的选择性应随着距中心地的旅行距离的增加而增加，以便觅食者通过选择利润更高的觅食栖息地来补偿旅行成本。使用全球定位系统（GPS）标签，我们通过雌性树燕子（Tachycineta bicolor）位于包含湿地的4个地点，而陆地覆盖以草地（草，草覆盖）和/或耕地为主。我们还使用sweep网样带来评估可吞咽的不同生境（湿地池塘边缘，草田边缘和代表性高地）中飞行昆虫的丰度和生物量。正如中心采食机所期望的那样，带GPS标签的燕子为湿地池塘选择了更多的东西（与可用性不成比例），并且似乎越来越选择与巢穴距离越来越远的湿地。在农田占主导地位的地区，池塘边缘或草场边缘的昆虫丰度和生物量往往高于耕地高地，而在以草和草覆盖为主的地点的采样生境中，昆虫的丰度和生物量则更为均匀。燕子栖息地的选择并没有通过抽样昆虫在栖息地之间的分布清楚地解释。但是，传统的陆地采样方法可能无法充分反映猎物的分布和空中觅食燕子的可用性。总体而言，我们的研究结果强调了保护和增强农业景观中的草原湿地和其他非作物生境的重要性，因为它们的使用和支持燕子和昆虫种群繁殖的能力不成比例。