What about some netting around the base of the magnnolia then at least it couldn't drop down on them without getting tangled.The attack site was under the magnolia tree which was their refuge from the Red Tailed Hawks which were their previous top predator. They do still go under the magnolia tree and even stopped to groom there today.
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The Cooper's Hawk is so much more dangerous than the Red Tailed Hawk even though it is smaller.