Ira's article on the Kangaroo

Among the several fields of knowledge Ira mastered entirely on his own was zoology. Here's something he wrote about the kangaroo for the Roger Williams Park Zoo newsletter:


MACROPODS, THE BIG KANGAROOS
(or how to organize birth into an assembly line)
Our Eastern Grey Kangaroos are considered the biggest of the kangaroos hence the Genus and species name Macropus gigantea. They are also, therefore, among the largest of the living Marsupials. At birth they are at most barely over a half inch and weigh less than an ounce; they look like embryos with undeveloped eyes, hind limbs, and tail. Using its strong forelimbs, the newly-born infant will climb up the mother's fur and into her forward-opening pouch. There it clamps its mouth onto one of four teats, remaining attached for as long as 300 days of development. The pouch provides a warm, humid environment for the juvenile, which cannot yet regulate its own temperature and can lose moisture rapidly through its hairless skin.
Once the juvenile has detached from the teat, the mother will allow it out for short walkabouts, retrieving it when she moves. She will prevent it from returning to the pouch just before the birth of her next young, but it will continue to follow her about as a dependent young-at-foot, and can put its head in the maternal pouch to suck the teat. The quality of milk provided changes as the joey matures, and a mother suckling a juvenile in the pouch at the same time as a young-at-foot will produce different qualities of milk from the two teats - a feat achieved by having the mammary glands under separate hormonal control.
All macropods produce only one young at birth and, with some exceptions, can conceive and give birth at any time of the year. Gestation for the Eastern Grey is about 36 days. Giving birth to such small babies is relatively effortless; the female sits with tail forward between her legs and licks the fur between her cloaca and pouch, producing a path that will keep the climbing neonate moist until it enters the pouch. A few days after giving birth the female will enter estrus once more. If they are mated and conceive, the new embryo's development halts at an unimplanted blastocyst stage. This stage lasts until about a month before the current pouch young is sufficiently developed to quit the pouch. Then the blastocyst implants in the uterus and resumes development. A day or two before birth is due, the mother will exclude the previous young from the pouch, a rebuff that is difficult for it to accept as it has been taught to come when called and climb back into the pouch. The mother then cleans and prepares the pouch for the next juvenile. Thus the female can simultaneously support a suckling young-atfoot, a suckling pouch young, and a dormant or developing embryo.

-Ira Wellins, Life Docent

Here's the link to the article as it appears on the web:
http://www.briegull.com/SOSongs/macropods.htm