Retreat, detour or advance? Understanding the movements of birds confronting the Gulf of Mexico
During migration, birds must locate stopover habitats that provide sufficient resources to rest and refuel while en route to the breeding or non-breeding area. Long-distance migrants invariably encounter inhospitable geographic features, the edges of which are often characterized by habitat limited in food and safety. In response, they often depart in directions inconsistent with reaching their destination, presumably searching for better habitat. We used automated radio telemetry to track 442 individuals of five species to investigate the behavior of migratory birds as they departed edge habitat along the northern Gulf of Mexico coast during autumn from 2008 to 2014. Most migrants (75%) retreated inland or detoured around rather than advanced across the Gulf, but this depended on bird species and fat-based energy stores. Most individuals in lean condition or of smaller bodied species tended to retreat or detour, rather than advance, when departing from the coast. Twenty-one percent of all birds that departed the coast in 2013–2014 were redetected over 45 km inland, providing a unique opportunity to compare stopover duration, departure times and travel speeds between migrants that retreat away from the coast and those that continue to advance toward their destination. Individuals that retreated the coast and were redetected inland spent ~1 day on the coast before retreating inland, where they spent 11 days before resuming migration. Further when those same individuals retreated from the coast, they departed around evening civil twilight, whereas those that advanced from inland habitats departed after evening civil twilight. Travel speeds were slower for individuals retreating inland compared to those advancing towards the coast from inland habitats. The differences between retreating and advancing individuals suggest how an individual's drive to feed or fly influences behavior. Our study illustrates how the sum of individual decisions can shape habitat use, landscape-scale movements and migration strategies.