The effect of Hurricane Sandy on landbird migration in the northeastern United States
Date
2016
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Publisher
University of Delaware
Abstract
The annual migration of birds between wintering and breeding grounds requires birds to traverse novel landscapes while minimizing mortality and energetic costs in route. In autumn, birds in the eastern United States migrate at a time when large scale hurricane systems typically make landfall along the coastal United States. These storms are capable of killing birds as well as modifying food resources and habitats for birds via extreme winds and storm surge. Hurricane Sandy was a large Category 1 hurricane that made landfall at Brigantine, New Jersey on October 29, 2012. Sandy brought high winds (>90mph), torrential rains, and storm surge up to 12m to the area. Sandy made landfall late in the migration season when landbird migrants like the American Robin (Turdus migratorius) and Yellow-rumped Warbler ( Setophaga coronate) were actively migrating through the storm-affected region. I used six radars across the coastal northeastern US from Boston, MA to Norfolk, VA to analyze how Sandy might have affected birds migrating around the time of the storm. Additionally, I investigated what birds aloft were being observed by weather radars around sunset by performing surveys of birds at sites where birds were concentrated around Delaware and New Jersey during late October and November of 2015. Bird counts consisted primarily of communally roosting species like American Robins, Common Grackles ( Quiscalus quiscula), and European Starlings (Sturnus vulgarus ). American Robins were the most common birds seen migrating south around sunset that matched radar observations of birds moving south. I used this information to test how habitat use of birds before and after Sandy changed, by analyzing radar reflectivity measured at sunset at the six radars for baseline years (2008–2011) compared to the Sandy year (2012). Densities of birds leaving stopover areas increased in developed areas and decreased in agricultural and wetland areas across the study area after the passage of Sandy. The largest decreases in bird density were within 150km of Sandy’s path, and changes to bird density were unrelated to distance to the coast and changes in vegetation (measured by Normalized Difference Vegetation Index). I tested whether these changes in bird density were due to a shift in migration intensity due to the storm. I analyzed traffic rates at all six radars for the baseline years and the Sandy year. Migration Traffic Rates were three times higher in regions around New York City and New Jersey the night Sandy entered the region (October 27). After the passage of the storm all radars observed significantly higher traffic rates compared to previous years. Two weeks after the storm, the majority of radars observed traffic rates similar to previous years. Current climate models predict an increase in hurricane severity in the future due to climate change. This research shows that birds are relatively plastic in their response to hurricanes, likely due to their high mobility, which may help to mitigate negative effects from future storms.