During a rainstorm, you're more likely to see birds perched and hunkered down than flying around. Most birds are mostly waterproof. Their feathers, combined with oil from preen glands, keep them pretty watertight.
Is it good to go birding in the rain?
Ask any experienced birder, and they'll tell you, not only can you go birding in the rain, you should go birding in the rain! Birdwatching in the rain can result in unique sightings as the weather changes the behavior of birds. Birds sit still in trees during rain, making them easier to spot.
Are birds affected by rain?
Land Birds
I'm sure you've observed that light rain does not affect most birds. Their feathers shed rain and trap air against their bodies to help keep them warm. But heavy rains prompt them to seek shelter in bushes and trees. They remain motionless and conserve energy much as they do at night.