Theory 13/Navigation
Departure Is Fuel Against Wind
The claim
Migratory departure timing is set by the ratio of fuel load to wind assistance, so birds depart with less fuel when the wind is favourable and wait when it is not.
01Mechanism
Flight range depends on fuel and wind; the ratio determines whether the crossing is possible, and the departure rule tracks it.
02Predictions
- P1Departure should track the ratio.
- P2Fuel load alone should mispredict.
03Refutation
Departure tracking date would remove the wind term.
04Why it resists the grid
A decision made at one place depends on conditions hundreds of kilometres away, which the bird has no direct access to.