![]() ![]() Migrants can concentrate along shorelines for a variety of reasons. Migrants within both the central and eastern flyways move through the Great Lakes region, and there is evidence that Great Lakes shorelines support a relatively high concentration of migrating birds and bats. Our ability to identify and protect a network of stopover habitats along these features is an important component of conserving migratory species. Within general flyways, migrant activity is concentrated along physiographic features such as rivers, ridgelines, or shorelines that are thought to be used for navigation or refuge. These movements are thought to occur in broad waves across the landscape, but not all habitats traversed are equally important. For example, NEXRAD radar and citizen science data suggest three broad flyways that are shaped by synoptic weather patterns and funnel migrants through regions of the continental United States. Technological advances and improved modeling techniques are beginning to close this information gap by identifying continent-level movement patterns as well as areas where migrants concentrate. Nonetheless, much remains unknown about how migrating birds and bats connect distant habitats. Identifying migration routes, habitats used, and causes of stress or mortality during this phase is as important as understanding the requirements of quality breeding and wintering grounds. Many species of birds and bats experience strong selective pressure during migration and the need for conservation during this vulnerable life cycle phase is clear. We suggest using a high degree of caution when assessing potential impacts from development in these sensitive environments, and encourage protection of these high-use areas. The high use of coasts by migrants highlights the importance of conserving shoreline stopover habitat, which often competes with anthropogenic uses. These findings help confirm and quantify the phenomenon of nocturnal migrant reorientation at dawn, and also stress the functional importance of coastal regions for aerial migrants. ![]() This shift in direction, which was most intense at the shoreline, may contribute to the higher concentrations of migrants observed at shorelines in this study and others. An analysis of flight directions found that migrants flew to the north and northwest during dusk and night, with many heading out over the lake, but shifted direction towards the east at dawn, as those flying over water reoriented towards land. We found shoreline activity to be 27% greater than inland activity over all time periods, and 132% greater during the hour surrounding dawn. ResultsÄuring the spring of 2014 we used two avian radar units to compare migration patterns at shoreline (1.5 km from the shore) and inland (20 km from the shore) sites along the eastern shoreline of Lake Michigan in the north-central US. Mobile avian radar can provide a unique view of how birds and bats move across landscapes by tracking thousands of individual migrants moving through a sample volume that extends multiple kilometers in radius. Shorelines are known areas of migrant concentration due to the ecological barrier effect, but details on the magnitude of this concentration and the flight behaviors causing it are largely unknown and difficult to quantify. ![]() Millions of flying migrants encounter the Great Lakes and other large water bodies on long-distance flights each spring and fall, but quantitative data regarding how they traverse these obstacles are limited. ![]()
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