It dawned on him how dangerous of a situation he currently is in.
He has only two choices left to make, both of which could result in his death.
His first choice is to find a way to kill off the bird, jump off its back and into the lava with hopes that his fire resistance skill will save him.
His second choice, is to try and control the bird into crashing on one of the volcanic mountains below with the hopes that he won't get burnt alive.
This two choices are extremely dangerous and rely heavily on how far his fire resistance skill can go.
He chose to risk it by picking the first option.
There is a chance that if he succeeds in killing the bird, he might level up making his body more sustainable to the heat, and if it doesn't go as he predicts, then death be it.
He sat on the neck of the hawk and wrapped his legs around it.
He activates his thorn manipulation skill and sprouts out thorn from his whole leg that was wrapped around the hawk's neck.