Assertion: magpie | /r/CapableOf | lose a few tail feathers
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text: Entirely speculative (this IS the talk page...), but possibly simply to predation - i.e. if a fox or cat grabs a magpie's tail, the magpie may just lose a few tail feathers and escape, if there's lots of lightweight tail, the predator is more likely to get a mouthful/pawful of tail rather than anything important.