Birds fly by forcing air downwards with their wings. On the upstroke, the feathers pivot to let the air pass through them, but on the downstroke they close – similar to a venetian blind – and push against the air. When it rains, the same principles apply. Strong winds and turbulent air during a storm can make it trickier to fly, but their feathers are quite waterproof and there is nothing inherent in the rain itself that prevents them flying. Birds even have ‘windscreen wipers’ in the form of a semi-transparent third eyelid that blinks sideways (known as a nictitating membrane) to keep their vision clear.
Answered by Luis Villazon