Variation in migratory behavior is the result of different individual strategies andfluctuations in individual performances. A first step toward understanding thesedifferences in migratory behavior among individuals is, therefore, to assess the relativecontributions of inter- and intra-individual differences to this variation. We did thisusing light-level geolocators deployed on the breeding grounds to follow continentalblack-tailed godwits (Limosa limosa limosa) throughout their south- and northwardmigrations over multiple years. Based on repeated tracks from 36 individuals, we foundtwo general patterns in godwit migratory behavior: First, migratory timing in black-tailedgodwits varies mostly because individual godwits migrate at different times of the year.Second, individuals also exhibit considerable variation in timing within their respectivemigratory windows. Although the absolute amount of inter-individual variation in timingdecreased over the course of northward migration, individual godwits still arrived at theirbreeding grounds across a span of more than 5 weeks. These differences in migratorytiming among individuals are larger than those currently observed in other migratory birdspecies and suggest that the selective forces that limit the variation in migratory timingin other species are relaxed or absent in godwits. Furthermore, we could not attributethese individual differences to the sex or wintering location of an individual. We suggestthat different developmental trajectories enabled by developmental plasticity likely resultin these generally consistent, life-long annual routines. To investigate this possibility andto gain an understanding of the different selection pressures that could be acting duringmigration and throughout a godwit’s life, future studies should track juvenile godwits andother migratory birds from birth to adulthood while also manipulating their spatiotemporalenvironment during development.
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