Projected impacts of sea level rise on stopover habitat availability for Nearctic-Neotropical migrants
Many barrier islands along the Gulf of Mexico may provide critical stopover habitats for Nearctic-Neotropical migrant songbirds because these islands are the first possible landfall for individuals following a trans-Gulf migration pathway. The effects of climate change, particularly sea level rise (SLR), may negatively impact habitat availability for migrants on barrier islands. Our research objective was to determine whether high quality habitat will be available for migrants during stopover on St. George Island, Florida following SLR. We performed a supervised classification on WorldView-2 satellite imagery to create habitat maps of the island. Then we collected transect data during spring migration to observe habitat use by migrants on the island (2013, N = 272; 2014, N = 439). We also measured canopy and understory heights using the clinometer method, and elevation using Real-Time Kinematic (RTK) GPS. Finally, we used the Sea Level Affecting Marshes Model (SLAMM 6.0) to simulate potential impacts of SLR (0.28 m, 0.82 m, and 2 m) on habitat availability.
By comparing the habitat map to data collected during transects, we found that migrants were more common in palustrine forested areas with high understory height and low elevation. A substantial percentage of palustrine forest (44%) will be lost by 2100 assuming 0.82 m SLR. According to our model, these forested areas will be converted to marshes and then erode to tidal flats. Thus less forested habitat will be available for migrants to rest and replenish energy during stopover. Population declines are already present for some migrant species, and mortality rates are higher during migration than stationary periods of breeding and wintering. Degradation of barrier island stopover habitat may further increase cost of migration. It is essential to protect stopover areas, especially near ecological barriers such as the Gulf of Mexico. Future management actions are necessary to protect barrier island ecosystems to sustain long-term viability of migrants.