Reproduction in the Grey Kangaroo, Macropus canguru, in captivity

Abstract

Observations were made on the grey kangaroo, housed in yards, initially at Adelaide, S.A., and later at Canberra, A.C.T., to provide basic information on reproduction and growth. This information was required for the interpretation of data obtained from concurrent field studies. Grey kangaroos are capable of breeding throughout the year but with increased frequency between the months of September and March, referred to as the "breeding season". Typical mating behaviour is described. Mating, which usually lasted about 50 min, was first used to indicate oestrus and ovulation, but it was later found possible to detect when ovulation had occurred from a characteristic vaginal smear which is described. During the "breeding season" the length of the oestrous cycle of the grey kangaroo in captivity varied from 32 to 55 days; a greater variation in length than in any other marsupial in which cyclic reproductive phenomena have been adequately described, Grey kangaroos from South Australia had gestation periods of 29-31 days; those from south-eastern New South Wales, 33-35 days; and those from mid-northern New South Wales, 38 days. The characteristic gestation period from each geographical strain of kangaroo was altered by from 9 % to 15 % if the females were mated with males of other strains. It is suggested that the genetic constitution of the embryo influences the period of intra-uterine development. Fertile post-partum mating with subsequent lactation-controlled delayed implantation of the type exhibited by other macropodids was not found in the grey kangaroo, and thus a new young was not produced after premature removal of the earlier young from the pouch, but if the removal took place during the "breeding season" then the female usually returned to oestrus within 13 days. Wild females, which had recently had fertile matings and with pouch young aged about 235 days, were collected at Mt. Hope, N.S.W., plus two others in a small sample at another site with pouch young aged 44 and 151 days, but it is not yet known whether the embryos complete development. If these are viable, their development must be slowed down during part of the following days, to ensure complete vacation of the pouch by the earlier occupant. Mating occurred in three domestic females with pouch young aged 82, 247, and 271 days, but further young were not produced from these matings. Because of the slow rate of development of the pouch young-a pouch life of 312 days compared with 240 days for the red kangaroo-and due to the restricted "breeding season", each sexually mature female grey kangaroo can produce and rear only one young each year. After leaving the pouch, each young may be suckled by its mother for at least another 6 months. * Division of Wildlife Research, CSIRO, Canberra. t Department of Zoology, University of Adelaide; present address: Mrs. J. Marsh, 2 Nicolle Ave., Hawthorndene, S.A.