White rhinos were extirpated in Zimbabwe in the late 1800s
Reintroductions 1962-1967 & 1975-1986. White rhinos were reintroduced in the 1960s when animals were translocated from Umfolozi Game Reserve in South Africa. Matobo National Park (MNP) is located in southwestern Zimbabwe, and encompasses over 425 km? of the Matobo Hills, characterised by rugged, granitic domes and kopjes. In 1962, four white rhinos were released into a fenced area of approximately 105 km? within MNP known as the Whovi Game Park (WGP). During 1966-67, eight individuals were added to this group bringing the founding number to 12 (seven females and five males). 1987 - An additional three females and one male were added to the population from Swaziland in 1987. The population increased rapidly within the fenced area, and 20 individuals were translocated out of the reserve between 1975 and 1986 because of increased levels of aggression and fight-related injuries. A second population of white rhinos was established within MNP in 1978-79 when six of the rhinos removed from the fenced WGP were released in a region known as the Hazelside Area (HA).
Population growth after reintroduction. The population of white rhinos in the fenced WGP has undergone two periods of growth during which translocations did not occur: 1967-1974 (early period) and 1987-1994 (late period). Rates of annual increase calculated for the early and late periods were 10.4 and 6.6 %, respectively. The ecological density in the WGP increased by >200% during this time, from 0.23 rhino/ km? in 1967 to 0.83 rhino/ km? in 1994. We examined data on recruitment rate of the WGP population as a function of population density. A simple linear regression revealed that recruitment rate of calves (calves that survived >2 years) decreased significantly (P = 0.007) with the density of adult and subadult rhinos (>2 years of age). Because rhinos are non-seasonal breeders and reproduce at intervals of 2-4 years, annual recruitment rates vary markedly, however, the decreasing trend in recruitment with population density is clear. Discussion Numerous factors probably interact to affect reproduction in female mammals. Several studies have identified a threshold body mass for reproduction among young female ungulates, and the relationship between reproduction and body mass may be influenced by population density. Other studies have distinguished between total body mass and body fat, demonstrating that fat reserves independent of body size can positively influence reproduction in females Although the index of body condition we used for the white rhinos is crude, it revealed seasonal declines in body condition related to both population density and reproductive status of females. This suggests that competition among individuals occurred in the high-density population and affected body condition during the dry season when forage availability is lower. Population growth - Rapid rates of increase have been reported in large herbivore populations following introduction into unoccupied habitats. The rate of growth of the white rhino population in the WGP following introduction (10.4% per annum) is among the highest rates documented for free-ranging populations of either species of African rhino. A maximum rate of 9.6 % per annum was calculated for white rhinos in Umfolozi Game Reserve, South Africa, and 10.5% was estimated to be a theoretical maximum for the species (Owen-Smith, 1988). A maximum rate of increase was estimated to be 6.0% in Ndumu Game Reserve, a small South African reserve. However, a growth rate of 9.7% was reported for a small, low-density population of northern white rhinos in Garamba National Park, Zaire. The white rhino population in the WGP appears to have achieved a near-maximal rate of growth following introduction into this unoccupied habitat. Recruitment rate in a closed system is a population-level index of reproduction. The decrease in the recruitmcnt of calves with population size in the WGP indicates that reproduction declined as the population density increased. Densities varied markedly between the early and late periods, and differences in recruitment during these two periods probably contributed to the observed differences in population growth rates.
Population growth after reintroduction. The population of white rhinos in the fenced WGP has undergone two periods of growth during which translocations did not occur: 1967-1974 (early period) and 1987-1994 (late period). Rates of annual increase calculated for the early and late periods were 10.4 and 6.6 %, respectively. The ecological density in the WGP increased by >200% during this time, from 0.23 rhino/ km? in 1967 to 0.83 rhino/ km? in 1994.
Females breed faster in low-density populations than in high density - Conservation Implication for rhino managers Due to extreme levels of poaching, few African rhinos now persist outside of heavily guarded reserves. Most rhino sanctuaries encompass relatively small areas because of the difficulty and expense of providing adequate anti-poaching protection in large, remote regions. Because rhino populations within these sanctuaries are likely to increase in the absence of poaching until density-dependent factors stabilise population growth, managers may eventually trade off reproduction for safety in following this conservation strategy. One way around this dilemma is to maintain populations in reserves below ecological carrying capacities. Indeed, management plans for rhinos in South Africa and Namibia have incorporated these ideas based on theoretical relationships between population growth and density. The long-term data from Matobo Park provide empirical results to quantify such relationships, and demonstrate that density-dependent responses can have profound effects, even within a period of 30 years. Maintenance of rhino populations in reserves at low densities, however, presents managers with another challenge. Because large-bodied species require large areas, total population sizes of rhinos within smaller reserves are likely to be low, and few will reach numbers recommended for long-term population viability. This situation already exists for black rhinos, for which >80 % of the remaining individuals survive in populations of fewer than 100 animals. Under these circumstances, managers may need to consider exchanging individuals among reserves in a metapopulation management approach. However, translocation of rhinos is both costly and logistically challenging. Non-biological factors also will bear on management decisions. Conservationists concerned about populations threatened by poaching may be constrained by limited resources for law enforcement, and may choose to maintain surviving individuals in higher-density populations within safe areas. From a numerical viewpoint, trading off numbers lost to poachers with the decrease in numbers of young recruited, this conservative strategy may be more prudent until resources can be secured to establish additional sanctuaries. However, if management goals are to increase numbers of rhinos and to restock safe areas within their former ranges, then population densities within rhino sanctuaries should be monitored and managed below the level where body condition affects reproduction.
Zimbabwe. Body condition was assessed following a method outlined for white rhinos by Keep (1971), which scores condition visually based on reduction of fat deposits and muscle mass around the neck, scapula, spine and sacrum. We photographed each rhino in the late wet season (7 April to 8 May) and again towards the end of the dry season (30 September to 2 November). Multiple photographs were taken of each rhino and scored on a scale from one to four at increments of 0.5. An average score was assigned to each individual in each season. We contrasted body condition of lactating and nonlactating females. All females with calves 2.5 years of age whom they were not observed to nurse, were classified as 'non-lactating'. Body condition and reproductive status Body condition varied only slightly among individuals during the wet season, but 90% lost condition during the dry season. Loss of body condition by females was related to reproductive status. Although condition of lactating females (n = 9) and non-lactating adult females (n = 7) differed little during the wet season, lactating females were in significantly poorer condition during the late dry season. Differences in body condition also were related to population density. Rhinos >2 years of age in the high-density population (n = 32) were in significantly poorer body condition than those in the low-density population (n = 7) at the end of the dry season. This difference was apparent despite the fact that lactating females, which tend to exhibit the poorest body condition, comprised a greater proportion of the low-density population.
Zimbabwe. Body condition was assessed following a method outlined for white rhinos by Keep (1971), which scores condition visually based on reduction of fat deposits and muscle mass around the neck, scapula, spine and sacrum. We photographed each rhino in the late wet season (7 April to 8 May) and again towards the end of the dry season (30 September to 2 November). Multiple photographs were taken of each rhino and scored on a scale from one to four at increments of 0.5. An average score was assigned to each individual in each season. We contrasted body condition of lactating and nonlactating females. All females with calves 2.5 years of age whom they were not observed to nurse, were classified as 'non-lactating'. Body condition and reproductive status Body condition varied only slightly among individuals during the wet season, but 90% lost condition during the dry season. Loss of body condition by females was related to reproductive status. Although condition of lactating females (n = 9) and non-lactating adult females (n = 7) differed little during the wet season, lactating females were in significantly poorer condition during the late dry season. Differences in body condition also were related to population density. Rhinos >2 years of age in the high-density population (n = 32) were in significantly poorer body condition than those in the low-density population (n = 7) at the end of the dry season. This difference was apparent despite the fact that lactating females, which tend to exhibit the poorest body condition, comprised a greater proportion of the low-density population.
Intervals between births have ranged from 2 to 6 years for white rhinos in MNP. Mean intervals for females in the WGP were 2.9 ? 0.1 years (n = 6 females, 21 intervals) during the early period and 3.3 ? 0.2 years (n = 8 females, 19 intervals) during the late period. Only one female in the low-density population has given birth to more than three calves, with a mean of 2.25 years for 5 birth intervals. This value is lower than the mean intervals for all adult females (n = 8) during the same time period in the high-density population. The binomial probability of this result occurring by chance is 0.018, suggesting that the females in the low-density group experienced significantly shorter birth intervals than females in the high-density group. Although intervals between calves appear to increase at higher population densities, data from more individuals are required to provide a robust test of this relationship. Discussion Birth intervals in rhinos and other non-seasonal breeders vary considerably, and may be relatively plastic with respect to population density. African elephant females in high-density populations exhibit longer intervals between births than those in lower-density areas. In black rhinos, a contrast between Hluhluwe (high density) and Umfolozi (lower density) reserves revealed that the mean calving intervals were 2.7 and 2.3 years, respectively. A mean birth interval of 2.6 years was documented for white rhinos in Umfolozi Reserve, with a range of 1.8 to 3.5 years. Although the sample sizes are small, data from MNP suggest that rate of calving was inversely related to population density.
Zimbabwe. Female reproductive parameters varied with population density. Age at first reproduction for female white rhinos in MNP varied from 6.5 to 11.5 years of age. Using data for all females, age at first reproduction increased significantly with total population density in the year of conception. A contrast of age at first calving between the low-density (HA) group and the high-density WGP rhinos revealed that age at first birth was significantly lower for HA females (n = 4) than for those in the WGP (n = 9). Mean age at first birth was 7.4 ? 0.4 years in the low-density group and 10.1 ? 0.7 years in the high-density population. This contrast includes only females born during the period of 1982-1994, the time period for which data are available for both groups. Discussion Females that reproduce early should gain a genetic advantage over those that delay reproduction. However, early growth and maturation may affect future fecundity or survivorship. The age at which mammalian females reach puberty and begin reproducing can vary markedly with population density. Age at first calving also appears to be sensitive to population density in African rhinos. In black rhinos, age at first birth was 6,5 years in a low-density population in Umfolozi Reserve, South Africa, and 12 years in a high-density population in the neighbouring Hluhluwe Reserve. In MPN, first births occurred at older ages in white rhinos as density increased, and females in the low-density population calved at significantly younger ages than did those in the high-density group.
