This is an inaccurate way to judge (but hey is there an accurate way) Lets say a pigeon fly’s 48mph in a no wind situation, if there’s a helping wind say of 10mph I add that to the 48mph giving a speed of 58mph but if the wind is on their nose at again say 10mph I half the wind speed and deduct that (5mph) from the 48mph giving a speed of 43mph.