FOOD PREFERENCES OF BLACK RHINOCEROS IN THE TSAVO NATIONAL PARK

Food preferences of the black rhinoceros population in Tsavo National Park, Kenya were studied from 1967 to 1969. Feeding rhinoceros were watched for a period of 1 h, and the plants which they selected and rejected were identified, either as they were feeding or when they had moved on. A technique was used which provided an indication of the relative importance of certain plants in the diet during the wet and dry seasons. A total of 70 h was spent actually watching feeding rhinoceros in six habitat types representative of the changing ecosystem; 3,600 feeding stations were examined. Black rhinoceros were observed eating 102 species from 32 botanical families. In all habitat types the rhinoceros is very selective for herbs and shrubs, and shows a marked preference for legumes. Available grasses are very rarely eaten. Results of food preference studies in other areas of East Africa are compared with the present study. It is suggested that the abundance and distribution of certain kinds of leguminose flora may be the key to an optimum black rhinoceros habitat.     

HOME RANGE, BEHAVIOUR, AND RECRUITMENT RATES OF TWO BLACK RHINOCEROS POPULATIONS

During the period 1964 – 1966 biological studies were conducted of two black rhinoeeros Diceros bicornis L. populations in northern Tanzania. One population occupies the caldera of Ngorongoro and the other the area in the vicinity of Olduvai Gorge. Detailed records were made of each rhinoeeros observatson and 182 individuais were seen in the two study areas during the three-year period.
The black rhinoeeros is a very sedentary species, and the size of the home range is governed by several factors which are described in the^text. The home range of an immature rhinoeeros is larger than that of an adult individual. The adult rhinoeeros, especially the male, is essentially a solitary animal, but immatures frequently join up with a companion.
Activity patterns are described and illustrated, and are similar in the two study areas. Behaviour of the species follows welldefined patterns, and territorial behaviour is uncommon. Vocal communication in the species is described. The significance of dung piles, used regularly by the species, is considered and the results of experiments iflsing faecal samples are described. Relations with two carnivores are discussed.
The recruztment rates of the two populations are almost identical, i.e. 7.0% at Ngorongoro and 7.2% at Olduvai. Various reproductive characteris-tics affecting recruitment rates, such as age at maturity, gestation period and interval between successive calves are described using records obtained from zoological gardens and from field observations.
The results of the studies indIcate that the rhinoeeros population of the Ngorongoro Conservation Area is considerably higher than was formerly believed. The future of the species in the area appears favourable, providing its habitats are not destroyed through encroaching cultivation.     

THE VALIDITY OF CENSUSING BLACK RHINOCEROS POPULATIONS FROM THE AIR

The efficacy of censusing black rhinoceros ( Diceros bicornis Linnaeus) populations from the air was tested. Repeated aerial counts were made of the black rhinoceros population centered on Qlduvai Gorge, Tanzania, where the number of rhinoceros on the ground is known accurately. Even under the most ideal conditions only 50% of the population was detected by observers in an aircraft, and factors accounting for this are considered. It is concluded that the light aircraft is of limited value in providing estimates of black rhinoceros populations, and estimates based purely on aerial counts are subject to considerable variation.     

THE CAPTURE AND TRANSLOCATION OF THE BLACK RHINOCEROS

Black rhinoceroses were hunted on foot, from a vehicle, or from a helicopter throughout their range of habitats. Animals weighing 370–1,260 kg could be handled an average of 13 min after darting with a mixture of etorphine (1.9 μg/kg) and acepromazine (19 μg/kg). Cases of respiratory depression at this dosage were reversed soon after immobilisation by the intravenous injection of cyprenorphine (1.0 μg/kg). The captured animal was transported to camp, lashed on its side to a sledge, for periods of up to 515 min without mishap. A rhinoceros that was unloaded 180 min after darting rose to its feet and tried to push its way through the corner of the pen until antidote was administered at 215 min. This action was not observed in animals that received a total dose of 3.4 μg/kg of cyprenorphine before being unloaded 90–413 min after darting. The addition of hyoscine (at doses as low as 18 μg/kg) to etorphine and acepromazine improved the tractability of rhinoceroses that were only partially immobilised. However, sometimes at this dosage and always at doses above 35 μg/kg, hyoscine prolonged the ‘pushing’ phase for 175–410 min after darting despite the administration of cyprenorphine (4.0 μg/kg). There were no mortalities due to drug action in the series of 59 healthy rhinoceroses that were dart-immobilised, but there were two deaths due to mishandling and one caused by subsequent mismanagement.     

AERIAL CENSUS OF BLACK RHINOCEROS USING STRATIFIED RANDOM SAMPLING

During 1967–1968 a census was conducted of the black rhinoceros (Diceros bicornis L.) population in part of the Tsavo ecological unit. The region concerned covers an area of approximately 23,300 km² (9,000 square miles). Large parts of the region were systematically covered in a light aircraft and all rhinoceros observed were recorded on a 1:250,000 map. Because of the visibility bias inherent in such censuses correction factors were placed on the raw aerial data and crude estimates obtained. These crude estimates were then checked by intensive work on the ground in several sectors, and adjustments made where necessary. Using these crude estimates approximately two-thirds of the area under consideration were stratified into five density strata: very high, high, medium, low, and very low. Within this area 250 randomly located 2.59 km² (1 square mile) plots were intensively searched from the aircraft and all rhinoceros observed on these plots recorded. In the very high, high, and medium density strata these intensive searches resulted, at the 95% level of significance, in a population estimate of 4,200±25% of the mean or an estimate of between 3,150 and 5,255 rhinoceros within these strata. In the low stratum the statistical analysis resulted in a population estimate of 306±83% of the mean or an estimate of between 47 and 565 rhinoceros at the 90% level of significance. In the very low stratum the population estimate, at the 50% level of significance, was 266 ± 50% of the mean or an estimate of between 133 and 400 rhinoceros. A comparison of the crude estimates and the refined statistical estimates illustrates close agreement. The remaining third of the area was covered systematically and correction factors were placed on the raw aerial data. Crude estimates suggest a population of 2,800–3,000 occupying this part of the area. Assuming that this crude estimate, together with the statistical estimates for the low and very low strata, are rough approximations of the actual populations, it is statistically probable that the true population of black rhinoceros in this region lies between 6,130 and 9,220.     

AGE CRITERIA AND VITAL STATISTICS OF A BLACK RHINOCEROS POPULATION

Tsavo National Park, in Kenya, probably contains the largest population of black rhinoceros (Diceros bicornis (L.)) left in existence. Large-scale damage of the vegetation initiated by elephants and aggravated by fire has changed considerable areas of the park. The ecology of the black rhinoceros in this changing environment has been studied; the present status and population structure is considered here, including the development of detailed ageing criteria for the species, an analysis of natural mortality and survivorship, and a record of the structure of the living populations within the major habitat types. Crania and mandibles were collected from 506 rhinoceros found dead in all areas of the park. This material was divided into 20 relative age classes based on dental characteristics. Crude chronological ages, based on an estimate of the maximum expectation of life and the examination of seven known-age dental records of captive animals, were assigned to each age class. These crude ages were then refined by examination of 16 dental records of known-age wild rhinoceros, and a chronological age scale established. A survivorship curve of the population was thus constructed. Annual mortality during the first and second year of life is about 16%, and the indicated mean annual mortality from 5–25 y is 9.8%. A theoretical model of the population structure is shown, and analysis of the annual mortality and recruitment at birth suggests that the population was stable during the 1960's. Assuming the data represent a stable population the mean expectation of life at birth is 8.4 y. Thirteen major habitat types are described. The characteristics of the rhinoceros population within each habitat type were established both from ground studies and aerial observations. Nearly 700 rhinoceros were identified and catalogued on the ground, in sample areas selected for intensive study. Population structures, cow: calf ratios, and recruitment appear to be average in most habitat types. The analysis of recruitment at birth and mortality during the first year of life, both from computations from the survivorship curve and from the structure of the living populations, support the validity of the ageing criteria, and further suggest that the population was stable during the 1960's. Finally, the relationship between the elephant and the rhinoceros in the changing environment is discussed with reference to recent findings in elephant ecology. In conclusion it is recommended that population reduction of the Tsavo elephants should be initiated.     

HEDONIC R-INDEX MEASUREMENT OF TEMPERATURE PREFERENCES FOR DRINKING BLACK COFFEE

R-index measures were obtained from judges who ranked black coffees for preferred drinking temperature. Preferred temperatures were above thermal pain and thermal damage thresholds. The least preferred temperature was below the oral thermal pain threshold. Similar results were obtained with a ranking for temperatures that judges felt were most likely to be served in a coffee shop. Observations of customers in coffee shops indicated that they began sipping coffee at similar high temperatures.     

BLACK RHINOCEROS IMMOBILIZATION UTILIZING A NEW TRANQUILLIZING AGENT

Eleven black rhinoceroses were successfully immobilized, ten of them in the Arusha Chini area of Tanzania and one, a penned animal, near Nairobi. Of the total number, two were immobilized with Etorphine hydrochloride (M. 99) and acetylpromazine; six with a combination of Etorphine, acetylpromazine and a new tranquillizer, Azaperone; and three with Etorphine and Azaperone. In addition, one attempt at immobilization with a relatively new analgesic, Fentanyl, was not satisfactory at the dosage used, the animal being immobilized later with Etorphine and included in the eleven rhino described. Injection was accomplished on the ten Tanzania animals with Cap-Chur equipment from a helicopter, and on the penned animal with a hand syringe. Specimens and data were collected from the immobilized rhino. They were then loaded into crates, given an antidote (nalorphine hydrobromide) intramuscularly, and then trucked to points of release or to holding pens. Immobilization data, weights, sexes, relative ages, rectal temperatures, respiratory rates and pulse rates are tabulated.     

EVIDENCE FROM THYMIDINE-3H-LABELED MERISTEMS OF VICIA FABA OF TWO CELL POPULATIONS

Treatments with tritiated thymidine (TdR-³H) have revealed the existence of two populations of mitotically active cells in meristems of lateral roots of Vicia faba. A rapidly dividing population, with a cycle time of 14 hr, constitutes about half the cells in the meristem. A second population of cells, with a cycle time in excess of 30 hr, is also present. Estimates of the relative size of this slowly dividing population are more difficult to make, but we calculate that this population includes 27–43% of meristem cells. The remaining fraction of the meristem is made up of cells that divide rarely or not at all. Since, at all times, both populations contribute to the mitotic index, the curve of the percentage of labeled mitoses that can be determined after a pulse label with TdR-³H differs from the curve expected of an ideal population in an important way: the peak value of the curve of the percentage of labeled mitoses is always less than 100%, usually between 75 and 80%. This heterogeneity within a meristem must be borne in mind in terms of the response of meristems to disruptive treatments, the mechanisms controlling mitotic cycle duration, and the spatial organization of a heterogeneous population in an organ that shows polarized growth.