[Explanation] The meaning of this idiom is that once the birds are all shot, the bow used to shoot them is put away. It is a metaphor for ministers or officials who have rendered great service being discarded or harmed after their tasks are accomplished.
[Source] This idiom originates from "The Records of the Grand Historian: The House of Yue" (Shiji: Yue Jia): "When the flying birds are gone, the good bow is stored; when the cunning hare is dead, the hunting dog is boiled."
During the late Spring and Autumn period, Wu and Yue were rivals. Yue was defeated by Wu and forced to surrender and seek peace.
King Goujian of Yue endured hardship and humiliation, appointing ministers Wen Zhong and Fan Li to reorganize the state. For ten years they built up their population and resources, and for another ten years they educated and trained the people, transforming the nation from weakness to strength. Finally, they defeated Wu and avenged their national humiliation. King Fuchai of Wu, defeated in battle, fled and repeatedly sought peace with Yue seven times, but Wen Zhong and Fan Li insisted on refusing. With no other choice, Fuchai tied a letter to an arrow and shot it into Fan Li's camp. The letter read: "When all the hares are caught, the hunting dog that caught them is no longer useful and is killed and cooked for meat; when the enemy state is destroyed, the strategists who devised plans to defeat the enemy are no longer useful and are discarded or eliminated. Why won't you two ministers allow Wu to survive, so as to leave yourselves some room?" Wen Zhong and Fan Li still refused to make peace, so Fuchai had no choice but to draw his sword and commit suicide.
After King Goujian of Yue destroyed Wu, during a celebratory banquet for his ministers in the Wu palace, he noticed that Fan Li was missing. The next day, they found Fan Li's outer robe by the shore of Taihu Lake, and everyone assumed Fan Li had committed suicide by drowning. However, not long after, someone delivered a letter to Wen Zhong, which read: "When the flying birds are all shot, the bow is stored away; when the hares are all caught, the hunting dogs are killed and cooked; when the enemy state is destroyed, the strategists are discarded or harmed. The King of Yue is someone with whom one can share hardship, but not prosperity. Minister, if you still do not leave him now, you will soon face the danger of losing your life." Only then did Wen Zhong realize that Fan Li was not dead, but had gone into seclusion. Although he did not entirely believe the words of the letter, from then on he frequently claimed illness and stopped attending court, which over time aroused Goujian's suspicion. One day, Goujian visited Wen Zhong personally, and upon leaving, left behind a sword. When Wen Zhong saw the characters "Shu Lou" inscribed on the scabbard, he recognized it as the very sword that King Fuchai of Wu had once used to force the loyal minister Wu Zixu to commit suicide. He understood Goujian's intention, regretting deeply that he had not heeded Fan Li's warning, and had no choice but to draw the sword and take his own life.