Jamieson, Fausset and Brown on Job 39:14-15

14-15. Yet (unlike the stork) she "leaveth," &c. Hence called by the Arabs "the impious bird." However, the fact is, she lays her eggs with great care and hatches them, as other birds do; but in hot countries the eggs do not need so constant incubation; she therefore often leaves them and sometimes forgets the place on her return. Moreover, the outer eggs, intended for food, she feeds to her young; these eggs, lying separate in the sand, exposed to the sun, gave rise to the idea of her altogether leaving them. God describes her as she seems to man; implying, though she may seem foolishly to neglect her young, yet really she is guided by a sure instinct from God, as much as animals of instincts widely different.