Went out on Friday. Not ideal conditions, murky all day, very cold and no or only light breeze. Had two rotaries on the go, one with a speed controller and the other not. I set the speed to about 70%. Some birds were decoying in OK. However towards the end of the day the battery on the rotary without the speed controller was failing and the result was that the arms were hardly turning. Low and behold birds decoyed into to this rotary far more readily, ignoring the other that was still turning at a pace.
Was this a coincidence?