The development and flexibility of timing to environmental variability in a migratory songbird

As spring phenology advances with climate change it may create a mismatch between the timing of critical resources and breeding, leading to population declines in some migratory species. To investigate whether long-distance migrants can adjust to their changing environment, I studied the flexibility within two parts of the annual cycle in the eastern subspecies of purple martin (Progne subis subis). First, I examined whether the period between the spring arrival date to the first egg-lay date, termed the ‘arrival-breeding interval’, was flexible to local environmental conditions or constrained by carry-over effects from migration. Direct tracking technologies paired with nest checks at breeding colonies across eastern North America were used to accomplish this first objective. Second, the period from hatch to fall departure was used to explore the influence of ontogenetic effects on the development of migration timing in juvenile birds. The second objective required an experimental manipulation of hatch date at wild purple martin colonies in southern Manitoba to delay the daylength, or photoperiod, experienced by the juveniles while in the nest. I found the arrival-breeding interval to be flexible to local environmental conditions at breeding sites, where shorter intervals were associated with higher temperatures while precipitation had a variable influence depending upon the geographic region. I found no evidence of carry-over effects on the duration of the interval and the interval did not influence fledging success. For my second objective, I found some support for the role of the ontogenetic effect on the development of migration timing in juveniles. Juveniles with experimentally delayed hatch dates did not advance their timing and migrated at a later date than controls. To conclude, my results demonstrate flexibility in timing to environmental conditions, where purple martins lay eggs earlier in warmer springs and that early-hatching juveniles may develop early migration schedules that may enable them to keep up with their changing environment. Future studies are needed to understand if longer arrival-breeding intervals are associated with more flexibility than shorter intervals and if the ontogenetic effects on timing in the nest set migratory timing around the annual cycle.

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