Lord Sharabha is an avatar of Lord Shiva, who incarnated in the most powerful form than a lion to pacify Lord Narasimha Swamy. Lord Sharabha appeared like a huge bird with wings and strong beak. Sharabha Jayanthi falls in Vaisakha mass. Sharabha JAyanthi is an auspicious occasion for shaivaites.
Legend of Sharabha Avatar of Lord Shiva:
After demolishing Demon Hiranyakashapa, Lord Narasimha was very ferocious, roaring with anger, and it was impossible to stop him for all Gods and even for Prahlad, for whom Lord Narayana incarnated as Lord Narasimha and destroyed Hiranyakashapa.
To make Lord Narasimha calm and peaceful or to pacify him, all Gods went to Lord Shiva. Lord Shiva manifested as Veerabhadra (one of the incarnations of Lord Shiva) and went to Lord Narasimha and asked him to be calm as he was an incarnated for Lok Kalyan (Universal peace). But Lord Narasimha refused Lord Veerabhadras words and told him to go away from the place.
Angered with Lord Narasimhas reply, Lord Veerabhadra spread his body up to the sky and spread all over the Universe. He made his lower half of the body as Sharabha (bird) and remained his upper half as it is.
Lord Sharabha (one of the incarnations of Lord Shiva), lifted Lord Narasimha with his tail and was about to hit him on to the space. Lord Narasimha realized his mistake and prayed to Lord Sharabha to forgive him. Sharabheswara knew that Lord Narasimha realized his mistake and will remain calm and forgiven Narasimha. Excited Narasimha removed his skin (Lions skin) and presented it to Lord Shiva. Thus, Lord Shiva was appeared in two avatars (Veerabhadra avatar and Sharabha avatar) to pacify Lord Narasimha.