The correct answer is option 1: Hornbill. An endemic species refers to a species that is native to a particular geographic region and is not found anywhere else in the world. So, in this context, the hornbill is an endemic species because it is unique to a specific region and is not found in any other locations.

Option 2, the Indian Rhino, is not an endemic species because it is found in multiple countries, including India, Nepal, and Bhutan.

Option 3, the Pink Head Duck, is also not an endemic species as it is found in multiple regions across Asia and is not confined to a specific area.

Option 4, the Nicobar pigeon, is an endemic species because it is only found in the Nicobar Islands of India and is not distributed elsewhere. So, it could be considered a correct answer as well.