Reproduction in natural populations of the red kangaroo, Megaleia rufa (Desmarest), in central Australia.

Abstract

Reproduction in the red kangaroo, Megaleia rufa (Desmarest), in the arid environment of central Australia is highly opportunistic, and depends on the weather through its control of the food supply for its success. This conclusion is based on the study of 460 males and 1610 females between the years 1958 and 1962. Males and females matured sexually at an average age of about 2.5 and 3 yr, respectively. Drought significantly retarded sexual maturity in females by 6.24± 1.26 months. All females bred when green herbage was abundant after good rains. However, when food was scarce during drought, many females entered anoestrus, the proportion doing so being a probit function of the severity of the drought (measured in units of "drought index" explained in the text). Half of them became anoestrous after 3-5 months of drought in summer. Drought on the more scantily grassed of the two areas studied (they were 15-20 miles apart) was 1.57 times more effective in inducing anoestrus than on the other. All pouch-young survived if good conditions held for about 8 months, but many died during drought, the proportion doing so being a probit function of the increase in severity of drought after they were born. Half of them perished after 1.5-2.5 months of drought in summer. Only 28.7% of all joeys born survived life in the pouch because of the prolonged dry weather. Pouch-young were significantly lighter, and joeys-at-heel were 13.5 ± 1.9 days older during drought than at other times. The birth of twin joeys was associated with an abundance of food. During severe drought, many females showed signs of having produced in quick succession one or more joeys which did not live long. Many of these females were anoestrous and suckling a small joey. Since most if not all females which became anoestrous did so during late pregnancy without aborting and subsequently suckled their pouch-young, it is suggested that the adaptive significance of delayed implantation is to ensure that females which have lost a joey and which are about to become anoestrous produce one more joey each. These joeys will be born well into any drought and therefore will have to live for a shorter time than older joeys to survive the drought. The advantage to the species can be gauged from the fact that 50 out of 145 females with young surviving the drought were anoestrous. The ages of their joeys averaged 60.1 ± 7.6 days.