1. The question asks to identify which of the given options is not a bird.
2. Option (A) Golden Mahseer (Tor putitora) is a species of large freshwater fish found in the Himalayan region and other rivers in the Indian subcontinent. It is not a bird.
3. Option (B) Indian Nightjar (Caprimulgus asiaticus) is a species of nocturnal bird found widely in South Asia.
4. Option (C) Spoonbill refers to several species of large, long-legged wading birds in the family Threskiornithidae, characterized by their distinctive spoon-shaped bill.
5. Option (D) White Ibis (Eudocimus albus) is a species of wading bird belonging to the Ibis family, found in coastal regions of the Americas.
6. Therefore, the Golden Mahseer is the only option that is not a bird.