”Kelvar” refers to all earthly living creatures of Arda that have the ability to move around on their own, such as Birds and all other animals. The term is the Tolkien Mythology equivalent to “Fauna”.
Like all living things in Arda they were all created by Eru Ilúvatar in the earliest times of the world. They were placed under the care of Yavanna by Manwë at the behest of Eru in the earliest days of the world. The Great Eagles of Manwë are considered to be the highest of all the Kelvar and were inhabited by spirits since around the time of the Awakening of the Elves. This accounted for their sapience.