The limits of modifying migration speed to adjust to climate change

Predicting the range of variation over which organisms can adjust to environmental change is a major challenge in ecology(1,2). This is exemplified in migratory birds which experience changes in different habitats throughout the annual cycle(3). Earlier studies showed European population trends declining strongest in migrant species with least adjustment in spring arrival time(4,5). Thus, the increasing mismatches with other trophic levels in seasonal breeding areas(6,7) probably contribute to their large-scale decline. Here we quantify the potential range of adjusting spring arrival dates through modifying migration speeds by reviewing 49 tracking studies. Among individual variation in migration speed was mainly determined by the relatively short stop-over duration. Assuming this population response reflects individual phenotypic plasticity, we calculated the potential for phenotypic plasticity to speed-up migration by reducing stop-over duration. Even a 50% reduction-would lead to a mere two-day advance in arrival, considering adjustments on the final 2,000 km of the spring journey. Hence, in contrast to previous studies(8-10), flexibility in the major determinant of migration duration seems insufficient to adjust to ongoing climate change, and is unlikely to explain some of the observed arrival advancements in long-distance migrants.