The Hawk and the Nightingale.
Reading edition
A Nightingale, sitting aloft upon an oak, was seen by a Hawk, who made a swoop down, and seized him. The Nightingale earnestly besought the Hawk to let him go, saying that he was not big enough to satisfy the hunger of a Hawk, who ought to pursue the larger birds. The Hawk said: "I should indeed have lost my senses if I should let go food ready to my hand, for the sake of pursuing birds which are not yet even within sight."
A bird in the hand is worth two in the bush.