What is study of birds called as ?

Ornithology

The answer is Ornithology.

Ornithology is the scientific study of birds. It encompasses all aspects of bird biology, including their evolution, anatomy, physiology, behavior, ecology, and conservation. Ornithology is a branch of zoology, the scientific study of animals.

Anthropology is the study of human beings and their cultures. Avionology is the study of aircraft. Entomology is the study of insects.