{"title":"Tree Swallow selection for wetlands in agricultural landscapes predicted by central-place foraging theory","authors":"Andrew S. Elgin, R. Clark, C. Morrissey","doi":"10.1093/condor/duaa039","DOIUrl":null,"url":null,"abstract":"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. LAY SUMMARY Miniature GPS tags were used to track breeding female Tree Swallows at agricultural sites. Across agroecosystems, Tree Swallows selected more for wetland ponds than available in the landscape. Swallows increasingly selected for wetland ponds with increasing distance from nests, consistent with central-place foraging theory. Insect abundance and biomass tended to be greater in pond margins and non-crop vegetation (field margins or grasslands) than in croplands, but insect distribution patterns did not fully explain swallow habitat selection.","PeriodicalId":50624,"journal":{"name":"Condor","volume":" ","pages":"1 - 12"},"PeriodicalIF":2.6000,"publicationDate":"2020-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1093/condor/duaa039","citationCount":"11","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Condor","FirstCategoryId":"99","ListUrlMain":"https://doi.org/10.1093/condor/duaa039","RegionNum":2,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"ORNITHOLOGY","Score":null,"Total":0}
引用次数: 11
Abstract
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. LAY SUMMARY Miniature GPS tags were used to track breeding female Tree Swallows at agricultural sites. Across agroecosystems, Tree Swallows selected more for wetland ponds than available in the landscape. Swallows increasingly selected for wetland ponds with increasing distance from nests, consistent with central-place foraging theory. Insect abundance and biomass tended to be greater in pond margins and non-crop vegetation (field margins or grasslands) than in croplands, but insect distribution patterns did not fully explain swallow habitat selection.
期刊介绍:
The Condor is the official publication of the Cooper Ornithological Society, a non-profit organization of over 2,000 professional and amateur ornithologists and one of the largest ornithological societies in the world. A quarterly international journal that publishes original research from all fields of avian biology, The Condor has been a highly respected forum in ornithology for more than 100 years. The journal is one of the top ranked ornithology publications. Types of paper published include feature articles (longer manuscripts) Short Communications (generally shorter papers or papers that deal with one primary finding), Commentaries (brief papers that comment on articles published previously in The Condor), and Book Reviews.