There are five species of macropod (kangaroos, wallabies, bettongs and potoroos) in Tasmania:
The term macropod is derived from the Greek, which means 'large footed'. Members of this group -- the kangaroos and wallabies -- are characterised by their large hind legs and usually move around by hopping. Over 50 species of macropod occur in Australia, and its biogeographic relative, New Guinea.
All macropods have a remarkable reproductive cycle. Being marsupials, they give birth after a very short gestation period to young which have developed little past the embryo stage. The young continue to grow within a pouch. But in the case of many macropods, reproduction is characterised by the ability to arrest the development of embryos and, in some arid-dwelling species, even forgo the oestrus cycle.
All (except the musky rat kangaroo of far northern Queensland) give birth to a single young which is reared in a pouch.
In many species, including all five Tasmanian species, the female will mate again very soon after giving birth. In the case of the bettong, mating can occur literally hours after birth. If a young is already established in the pouch, the new embryo stops developing when it is little more than a ball of cells (the blastocyst stage).This process is known as embyonic diapause, or delayed inplantation. The suckling of the young already in the pouch initiates a hormonal response which triggers the arrested development of the embryo. The new embryo does not start to develop until either the young already present in the pouch is almost ready to leave the pouch or dies.
All macropods have a forward-opening pouch with four teats. When the new young is born it makes its way into the pouch and attaches itself to a different teat, usually the one diagonally opposite the one previously suckled. Again, soon after the birth the mother will mate. As this cycle continues, it is possible for a female to be suckling a pouch young, a larger young outside the pouch, and be carrying an undeveloped embryo.
This cycle is aided by a remarkable ability to produce two quite different types of milk at once. Through one nipple will come milk suited to the growing pouch young and through another will come milk specifically for the larger young outside the pouch! Each will contain differing compositions of lipids, carbohydrates and proteins.