And kereru and blackbirds spread the fruits all round the native bush!.
We inherited rowan trees here with their lovely red autumn fruits. Then checking through a DOC weed species register about 5 years ago, I realised that these were being sown by blackbirds all through the mountain beech forest. We have now chopped out all the rowan but it is amazing how the rowan seedlings still keep appearing.
Blackberry is perhaps the worst invasive weed spread by birds down here in the south and I had a Hawaiian ecologist here who described blackberry as the worst weed in Hawaii.