Tennis balls play an important role in the garden during the colder months of the year. Animals, especially birds and aquatic insects, depend on water.
A frozen water source can be extremely detrimental to animal life. Tennis balls prevent the formation of a layer of ice, allowing animals to access water. The practice is recommended by organizations such as the Royal Society for the Prevention of Cruelty to Animals (RSPCA) In the UK, tennis balls are less expensive than other devices available for sale, such as frost bells.