Mrigaswapnodbhava Parva is the fortieth upa parva included in the third maha parva, named as Vana parva or Aranyaka parva in the epic Mahabharata. The original epic was composed by Vyasa in Sanskrit. Vyshampayana had narrated to Janamejaya the historical events, happened in the forests on his queries.
How the presence of Pandavas occasionally affected the forest animals adversely?
Ghatotkacha had visited Bhima frequently since Bhima was his father. Since he was a demon, he liked to eat forest animals. Also, the brother in law of Nakula, Drishtaketu, occasionally visited Pandava brothers. Krishna had killed Ekalavya and later the eldest son of Ekalavya had been crowned for Indraprastha. He was also in good terms with Padavas and occasionally visited them in exile.
These visitors of Pandavas occasionally adversely affected forest animals due to their hunting habits. But Pandava brothers preferred only vegetarian food and were satisfied by the daily balance food of Akshayapatra. First, Draupadi was serving the poor Brahmins using the food received from the Akshayapatra and then the Pandava brothers were eating the balance food. Yudhishtira, Arjuna, Sahadeva and Draupadi were eating only vegetarian food.