Raining animals is a rare meteorological phenomenon, although there have been occurrences reported from many countries throughout history. It is believed that this phenomenon occurs at least occasionally when strong winds that are traveling over water pick up live debris (fish, frogs, etc.) and carry them up to several miles depositing them over land. Though this is one theory, it has never been witnessed or significantly tested.
Animals that are most likely to drop from the sky during a rainfall are fish and frogs. Birds are the most likely candidate after these two. The animals sometimes survive the fall, which is suggested that they are dropped shortly after being picked up. Several witnesses of raining frogs describe the animals as being startled, but otherwise healthy. In other instances, the animals are frozen to death and sometimes totally encased in ice. There are other reports where the actual rain is not from intact animals, but shredded body parts. The most common weather events for the production of raining animals are storms with strong winds, such as tornadoes, and hurricanes. However, there have been many unconfirmed cases in which rainfalls of animals have occurred in fair weather without the presence of wind or water.
A more recent scientific explanation of this phenomenon has been developed involving waterspouts. It is known that waterspouts, much like tornadoes, are capable of capturing debris and animals and lifting them into the air up to high altitudes and carrying them over long distances. In turn, the winds are capable of dispersing the objects over a relatively wide range. Tornadoes have been known to suck up an entire pond, letting the animals and water fall some distance away.
In the case of raining birds, storms may overcome a flock in flight, especially during a migration. There is one confirmed report of bats in flight being overtaken by a thunderstorm. It is more than possible for birds to rain over an area, especially when a storm produces a strong downdraft and as birds are overtaken, they are forced to the ground. It is harder to believe reports of terrestrial animals falling from the sky, although unconfirmed reports continue to flourish. Sometimes possible rain of animal events can be explained easily. For example, in Singapore in 1861, French naturalist Francis de Laporte de Castelnau explained that a rain of walking catfish that was believed to be rained down from the sky after people noticed them on the land, was in fact due to the actual migration pattern of the walking catfish. The fish is capable of dragging itself across land from one puddle to another and will often due so after a rain.