I have some boomerangs of the returning type. They could be used to knock down flying birds when you throw them into a flock. They require more practice than an elastic slingshot as they fly in a curve and depend on the wind. Using them for prey on the ground is virtually impossible. It would be easier to collect sticks or rocks when you find them.
Injuring waterfowl on the water often means that you wonīt get them as they can outswim and outdive you. Once they learn that the rock means danger they can even dodge it. It would be better to find a place where they come close to the shore and get them there. You may even try a baited fishing line.
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If it isnīt broken, it doesnīt have enough features yet.