Regardless of what kind of animal you are, stormy weather can be a real pain. It usually means there is little to be done other than finding a cozy space to hunker down to wait out the wet weather.
Most animals have developed behavioral or biological adaptations to help them stay warm and dry during light rains but heavy rains are another matter altogether. Many birds, for example, have a uropygial gland, also known as a preen gland, that helps waterproof their feathers. The gland, located near the base of the tail, produces a water resistant oil that is spread during preening. In heavy rains, however, this waterproofing is not enough to protect most birds from inclement weather. Waterfowl are the exception. They have a more developed uropygial gland and delight in the opportunity to explore newly flooded areas without the fear of heavy predation.
Small birds have to wait out the rain. Cavity nesters cozy up in their sheltered homes while songbirds perch motionless amongst the foliage. These birds are in conservation mode. They will stay put and use most of their energy for warmth while they wait for the worst of the storm to pass. If the rain persists, eventually the birds will have to venture out into the rain to search for food.
Larger birds, such as hawks, owls, and other raptors return to the hunt much sooner than their smaller relatives, relying on their large mass to keep them warm after their feathers get soaked through.
PRO TIP: One of the best times to go birding is after a big rainstorm. As soon as the weather clears, there is an explosion of foraging activity as the birds try and make up for lost time and restore their energy stores with a good meal.