Movement ecology reveals high temporal, but low geographic, plasticity in wood stork migration
Movement is the primary behavioral adaptation to dynamic environments. Large-scale movements, and migration in particular, allow species to alter their distribution and range in response to seasonal environmental variation (e.g. photoperiod, temperature, rainfall). To understand the capacity of species to adapt to global change, it is thus essential to accurately determine migration routes and assess individual variation in migration performance (timing and location). We studied movement of wood storks (Mycteria americana), a threatened species in the Southeastern U.S., using GPS telemetry over 7 years. Wood storks are facultative migrants, with migration routes sometimes exceeding 1,000 km, ranging from Mississippi and North Carolina in the summer to South Florida in winter. We first trained a classification algorithm on a few individuals (representing 5 % of the whole data set) with typical movement trajectories throughout the year, to be able to predict movement modes (foraging, commuting, traveling and migrating) for the whole data set. We then used line density methods to identify migratory corridors. Finally, we investigated temporal and geographic variation of individual migration routes with respect to environmental conditions using linear regressions.
Movement modes were classified correctly ≥ 90 % of the time, and migration accounted for less than 1 % of a total of nearly 500,000 wood stork locations. Of 56 adults monitored over at least one complete migration season, 33 (58 %) migrated at least once. Two main migration corridors were identified, along the eastern coastline of Florida during spring (northward migration) and western coastline during fall (southward migration). Although individual one-way migration typically lasts between 5 to 15 days, we highlighted a large temporal variation in the population, both within and between years; spring migration generally occurred during a four month period (February 25–June 20), and fall migration during a two month period (September 20–November 20). Individual adults, however, tended to be relatively consistent over the years, both in space (using the same route) and time (migrating at the same period), regardless of climatic conditions. In conclusion, we identified a minor portion of the data with high ecological importance, which are migratory movements. Wood storks migration revealed high temporal plasticity that may give room for adaptation, though constrained by low geographic variation.