As B.L.E. mentioned, as the servos strain under the pull/push of the airflow, they draw more current.

Hook up a watt meter, and move the sticks around. You'll get an average "peak" draw on the ground..

Now do the same thing again but "resist" the movement of the surfaces as you do this.

You will be quite surprised at how much current those little servos can draw under load.

On a 40-90oz/in servo it is not uncommon to see max draws of over 1800mA.

Typically the servo draws less than this amount in acutual flight, but the 250mA levels stated are a "best case" situation.

Multiply the higher draws by the number of surfaces being affected at once, plus the effect of any binding.