Reproduction in the two species of grey kangaroo, Macropus giganteus Shaw and M. fuliginosus (Desmarest) I. Sexual maturity and oestrus

Eastern grey kangaroos, M. giganteus, and the western grey kangaroos M. f. fuliginosus, M.J melanops and M. f, ocydromus were bred in enclosures over a period of 10 y. Testis biopsies indicated sexual maturity in males, as follows: in both species, changes in the tubules from age 15 months; some spermatozoa seen by 20 months; active spermatogenesis with sperm free in the lumen by 31 (some western greys) or 48 months (eastern greys). In females, onset of sexual maturation, indicated by eversion of the teats, was from 14 and 18 months in western and eastern greys respectively; initial mating at c. 16.4 and 19 months with births not less than 1 month later. Crosses occurred only between western males and eastern females. Male hybrids were sterile; females were fertile, invariably mated with western males but also twice with eastern males. Smears taken from the anterior urogenital sinus showed that in both species and in their hybrids oestrus was accompanied by a marked increase in long narrow epithelial cells ('long cells'). The cycle was 34.85+-4.42 days in western females, 38.06h+-3.51 days in hybrids and 45.58+-19.82 days in eastern females. Variation in cycle length between and within females in each species was not significant, although variation between fuliginosus and melanops was significant at the 5% level. Oestrus occurred in all months of the year but least often in winter when some females entered anoestrus. Variance ratios for cycle length in relation to month of year were not significant for eastern or hybrid females but were, at the 5 % level, for western females. On loss or removal of pouch young the mean delay in return to oestrus was 10.92f 4.78 days in eastern and 8.2515.84 days in western females, significantly different at the 5% level. Females which retain their young may return to oestrus by 150 days after the birth and may mate at any or all of up to nine oestruses before conceiving again. Differences between eastern and western females were not significant, but those between western subspecies were, particularly between fuliginosus and melanops at the 0.1 % level. Embryonic diapause was observed seven times, all in eastern females, and followed matings not less than 160 days after the birth of a current pouch young.