Complex sentence: Both birds build the nest on a main fork or a limb high in a tree, 12-20m high made of dead twigs and lined with grass or other vegetation and sheep's wool.
Split into simpler sentences: Both birds build the nest on a main fork or a limb high in a tree, 12-20 metres above the ground. IThe nest is made of twigs and lined with grass or other vegetation and sheep's wool.