Complex sentence: Female wombats give birth to a single young in the spring, after a gestation period, which like all marsupials can vary, in the case of the wombat: 20--21 days.
Split into simpler sentences: Female wombats give birth to a single young in the spring. After a gestation period, which like all marsupials can vary, in the case of the wombat: 20--21 days.