Would a kookaburra win a fight against a magpie?

Maybe: kookaburras are slightly more solidly built than magpies, and they stay in family groups, so that if a magpie attacked a kookaburra, there would most likely be more kookaburras that ame in to drive off the magpie. However, magpies are strong birds, very intelligent, sometimes aggressive, and adept fighters, so in one-to-one combat, the magpie would probably stand a better chance.