Which version of Mahabharata you read? In BORi Critical edition, they cursed each other. And bird wasn't god

He then saw his father, who asked him about his welfare and he replied, “I have been sent by the snakes to steal the supreme soma. I shall bring it today, to free my mother from her slavery. My mother instructed me to eat the nishadas. But even after eating them in their thousands, my hunger is not yet satisfied. O illustrious one! O lord! Show me some other food that I can eat, so that I am strong enough to steal the amrita.”

Kashyapa said, In ancient times, there was a maharshi named Vibhavasu. He became angry very easily. He had a younger brother named Supratika, who was a great ascetic. That great sage was unwilling to maintain their wealth jointly with his brother and Supratika always spoke of dividing it. After some time, Vibhavasu told his brother Supratika, ‘It is from delusion that many wish to divide common property. Once it has been divided, they are deluded from love of wealth. Ignorant from selfishness, enmity is created, though there is a disguise of friendship. Others, knowing them estranged in property matters, increase the enmity on other matters and divided relatives meet their downfall. Absolute ruin soon comes to those who are separated. That is the reason why learned ones never approve partition among brothers. When divided, they do not have any respect for the sacred texts or preceptors. O Supratika! You are beyond my control. Disregarding my advice and out of love for riches, you wish for a partition. I curse you that you will become an elephant.’ Thus cursed, Supratika told Vibhavasu, ‘You will become a tortoise that lives in the water.’ Cursed by each other and their minds deluded by desire, they became an elephant and a tortoise, animals of low birth. Boastful of their strengths and sizes, as earlier, they have continued in their vice of enmity towards each other, living in this huge lake. Look at one of them, the large and handsome elephant, come towards this lake now. Hearing his trumpeting, the giant tortoise that lives under water rises out of the lake, agitating its waters. On seeing him, the valorous elephant curls his trunk and rushes into the water, violently moving his tusks, trunk, tail and feet. The water that is full of fishes is agitated. The valorous tortoise also raises its head and comes up to fight. The elephant is six yojanas(A yojana is between 13 and 15 kilometres) in height and double that in length. The tortoise is three yojanas in height and ten yojanas in circumference. These two are maddened at the prospect of fighting each other and wish to kill each other. Eat them up and swiftly accomplish the task you wish to perform.” Hearing his father’s words, the bird swooped down from the sky and swiftly grasped the elephant and the tortoise, one in each claw. Full story here