Theory 028/Life & Evolution /Phenology
Migration Is Timed by Photoperiod
Warming is expected to advance migration. Species that read the calendar may not move at all.
Migration timing is set by the integration of photoperiod rather than by temperature, so warming advances arrival only where photoperiod cues are weak, and strongly photoperiodic species should show little advance.
01The evidence
Migration timing varies among species in how strongly it tracks temperature, with some species showing no advance despite warming.
02The tension
Phenology models use temperature as the cue because it correlates with timing in many species. The correlation fails for photoperiodic species and the failure is treated as a species-specific parameter.
03The mechanism
Photoperiod is a stable cue that integrates day length over weeks. Species that use it are buffered against short-term temperature variation and therefore do not advance when spring warms.
That makes the cue the predictor, and predicts that advance should be largest in species with weak photoperiodic control.
04What this is not
Temperature models predict advance everywhere. This predicts advance only where the cue is thermal.
05Predictions
- P1Advance should scale inversely with photoperiodic control.
- P2Strongly photoperiodic species should not advance.
- P3Cue manipulation should shift timing only in thermal species.
06Refutation
Uniform advance across cue types at fixed warming would restore the temperature model.
07What it changes
It would improve forecasts of phenological mismatch.