Age at sexual maturity. Appear to be no substantiated observations, but Vaughan-Kirby (1920) and Lang (1920) estimated 4-5 years. Age at first parturition. From above may be 5 ? to 6 ? years. Reported 6-7 years in Umfolozi GR (Owen Smith 1971).
Records of longevity in captivity (Reynolds 1962): there are numerous instances of captive animals exceeding 20 years of age, and the following three exceeding 30 years: Male 34 yrs 14 days in Johannesburg Male 34 years in Chicago Female 36 years in Chicago and still living In addition, Goddard (1970) found an old female, estimated 30 ? 4 yrs of age and from a wild population at Olduvai, to be pregnant. In his consideration of thevital statistics of Tsavo population Goddard assumed a maximum ecological longevity of about 40 years.
Population sex ratios: n=409 males 213 females 188 n=226 males 116 females 110 Concludes sex ration 1:1 (Vincent 1969)
Gestation period 548-578 days (Kenneth & Ritchie 1953) 614 days (Anon. 1968) 584 days (Wilson 1969) 476 days (Vincent 1969) 482 days (Vincent 1969)
Gestation periods. 469 days (Dittrich 1967) 446, 478 days (Goddard 1967) 457 days (Gowda 1967) 438, 419, 438 days (Greed 1967. 4 observations of slightly greater than 17 months, another of 15 months (Hallstrom 1967) 463, 454, 457 days (Hays 1967) 465, 462 days (Yamamoto 1967) Mean length of gestation period about 454 days.
Female 21 years (Huntley 1967). female 36 years old still bearing calves (Player & Feely 1960).
Calving interval: 2 ? years, 2 1/4 years, 2 ? - 3 years in Kruger NP. 4.33 years at Loskop Dam. However, Owen-Smith has observed in Umfolozi GR oestrus at 6-7 months post-partum, indicating that calving interval may be as little as 21-22 months.
Observations of time intervals between successive births of same female: 40+ months, 32+ months (Greed 1967) 2 observations of 30 months (Hays 1967) 23 ? months (Yamamoto 1967) 2 observations of 24 months, 35 ? months (Goddard 1967) 25, 28, 29 months (Goddard 1967) Roth & Child (1968) deduce from data from zoos (15 ? -16 months gestation and a 12-day period before the first oestrous post partem) a theoretical potential birth rate of 72-75 calves per 100 secxually mature females per year, i.e. 1 calf per adult every 16-16 ? months. These workers observed in the lake Kariba basin what they estimate a birth rate of about 50 calves to every 100 adult females, i.e. 1 calf every 2 years for each adult female. Goddard syas that a normal healthy female could be expected to produce a calf every 27 months. This may be accepted as a realistic potential.
No good evidence to indicate any seasonal peaks of reproductibe activity (Ansell 1960). However, Joubert (1969) and Von Richter (unpubl.) recorded the following birth dates in the Kaokoveld: Dec 1967, Jan 1967, March 1966 (2), March 1967, March 1968, April 1967, May 1966, May 1967, June 1967, August 1967. In view of the black rhino's long gestation period, Joubert's suggestion of photoperiod being implicated in apparent seasonal breeding is not entirely acceptable, but the alternative flushing of trees and shrubs (on which the rhino feed) in the rainy season may stimulate oestrous and result in a peak of conceptions.
Data indicate a wide spread of births. However, Owen-Smith (1971) reports the onset of oestrous apparently stimulated by a flush of green grass, so that there is a mating peak in spring and subsequent calving peak in autumn nearly 1 ? year later.
