Answer: A. They are pests.
Step-by-step explanation:
The speaker in this excerpt is telling the other person to shoot as many bluejays as they like. This means that the speaker attaches little value to the bluejays which can only mean that they are pests because people don't care much about killing pests.
We cannot infer that the bluejays are more plentiful than the mockingbirds from the excerpt because they could be the same number but it is simply wrong to kill mockingbirds.