At least eight peacocks died Monday due to heat stroke in Hasanpur village, 12 km from here in the Aravalli hills, a wildlife official said.
Two seriously ill peacocks have been taken for treatment to a veterinary hospital in Gurgaon district.
Villagers informed the wildlife department about the dead peacocks.
"We visited the spot and post-mortems were conducted on three peacocks, including a peahen," said District Forest Officer (DFO) Shyam Sunder.
Wild Life Conservator Vinod Kumar said: "We are investigating the matter. Reports of other peacocks dying earlier have also come to us, and we are not sure about the total number of deaths."
Jeet Ram, a social worker, said that at least eight peacocks had died during the past 24 hours till Monday. He said that ponds drying up in the Aravalli and nearby villages could be the main reason behind the deaths of the national bird.
"Some peacocks were buried, while others have been eaten up by animals," said Jeet Ram.
"Heat stroke was the cause of the deaths," said Devender Singh Joon, the veterinarian who conducted the post-mortems.
According to experts, the temperature in the treeless hilly areas where the peacocks died, remains two to three degree higher than in the fields.