Explanation:

More than 1,400 migratory birds were found dead recently due to an unexplained cause in the Pong Dam area of Kangra district in Himachal Pradesh.

• The Pong Dam is also known as the Beas Dam.
• It is an earth-fill embankment dam on the Beas River in Himachal Pradesh.
• The lake created by the dam, Maharana Pratap Sagar, is a renowned bird sanctuary.
• The purpose of the dam is water storage for irrigation and hydroelectric power generation.
• Wildlife authorities have sent samples taken from the carcass of the birds for testing at the High Security Animal Disease Laboratory in Bhopal to ascertain the cause of death.

Hence option 1st is correct.