Africa was once known for abundant populations of the now Critically Endangered Black rhino (Diceros bicornis). However, large-scale poaching in many parts of this continent during 1970- 1980 led to a 95% decline in the rhino numbers. Like in other countries that host remnant populations of the Black rhino, Tanzania’s Black rhinos are now largely restricted to protected areas such as the Ngorongoro Conservation Area (NCA). This study sought to map the spatial distribution of the Black rhino population in the Ngorongoro Crater (NC), assess the temporal trends in selected population attributes (size, growth rate, sex ratio and age-structure) over the past 15 years and evaluate food selection by the Black rhino. Black rhino population trends and spatial distribution were assessed using records obtained from NCA and ranger posts. Ecological surveys were conducted at Black rhino foraging sites to assess food availability and diet selection during wet and dry seasons. There was a steady growth in population of Black rhino from the initial 14 in 2000 to 44 in 2014. The highest growth rate (1.3 individuals /year) occurred in 2005, while the lowest growth rates (0 individuals) occurred in year 2006, 2011 and 2013. The sex ratios were skewed in favor of females (2:1) and approximately constant for the entire 15-year period. Spatial distribution patterns varied across seasons, with rhinos occupying the crater floor during the wet season and crater walls and rims during the dry season. In addition, the spatial distribution patterns were influenced by anthropogenic activities; rhinos avoided areas proximate to busy roads, lodges and livestock. Grasses and forbs occurred in nearly equal proportions at the Black rhino feeding sites, constituting 50.4% and 49.6%, respectively. During the wet season, rhinos mostly selected Commelina banagalensis, Amaranthus hybridus, Gutenbergia cordifolia, Justicia betonica and Lippia ukambensis while in dry season; Hibiscus aponeurus, Justicia betonica and A. xanthophloea. There were significant differences in forage items utilized in each season. A. hybridus (p=0.001) were more utilized in wet than dry season as well as C. bengalensis (p=0.008), E. arabicum (p=0.001), A. longiscupsis (p=0.019) and G. cordifolia (p=0.010). These results recommend that human activities such as livestock grazing, tourism infrastructure etc. should be minimized in crater to avoid disruption of rhino movement and habitat selection patterns. As well, it is vital to maintain the monitoring regime, and possibly improve the ratio of ranger to rhinos or area of patrol to enhance effective monitoring and management.

Background Information
Black rhinos (Diceros bicornis) were once abundant in many parts of Africa, especially in eastern and southern Africa (Dobson et al., 1992). However, since 1970s most of the Black rhino populations have effectively been eliminated from a large part of their historical range. It is estimated that the Black rhino numbers has reduced by 95% from 65,000 to 3,500 individuals in 1990 (Hearne and Swart, 1991). The massive declines in Black rhino numbers have been attributed to rampant poaching within its ranges. Currently, native Black rhino populations are only found in Tanzania, Kenya, South Africa and Botswana. Most of the extant Black rhino populations in these countries are found within government protected areas and well managed private wildlife conservancies (Blake et al., 2007). In Tanzania, the remnant Black rhino populations primarily occur in Ngorongoro Conservation Area, Selous Game Reserve, Serengeti National Park and Mkomazi National Park (Emslie et al. (2007).

Ngorongoro Conservation Area (NCA) is vital especially for Black rhino conservation because it is one of the only two ecosystems in Tanzania that host native Black rhino populations. The Black rhino population in the NCA is almost exclusively concentrated in the Ngorongoro Crater, which forms just 4 percent of the NCA area. The population of Black rhinos in NCA has dramatically declined since the mid-20thcentury, and especially since 1960s as a result of illegal poaching to supply the growing demand for rhino’s horn (Emslie et al. 2007; Blake et al., 2007) The NCA Black rhino population decline continued throughout 1980s and it is estimated that over 95% of the population that existed in 1960s (approximately 108 individuals) was eliminated (Bret, 2010).

Due to concerted efforts by the government and conservation agencies to curb poaching and enhance conservation, it is believed that the NCA Black rhino population is on the path to recovery although there have been no supporting scientific data. These conservation measures include stringent law enforcement and enhanced security measures within the NCA, including regular car patrols, regular monitoring of rhinos through radio transmitters and regular censuses. However, these measures have not been accompanied by requisite analyses of population dynamics, food availability and foraging ecology of the Black rhino in the NCA. The role of food availability and feeding ecology is critical in understanding how different habitat parameters can affect the spatial distribution, habitat use and population growth and numbers within a given site. Such analyses could vitally augment the existing conservation measures and contribute to enhanced conservation and management of this threatened species.

Statement of the problem
In order to curb poaching and enhance the recovery of the Black rhino population in the Ngorongoro Conservation Area, several conservation and security measures have been put in place, including 24-hour surveillance of the crater through car and foot patrols. In addition, population censuses are carried out regularly. However, little is known about Black rhino population trends in this ecosystem over the past years since the inception of these conservation efforts. Understanding the demographics of the species is important in assessing the resilience, long-term persistence or vulnerability of this population to vagaries of extinction or extirpation. In addition, relative availabilities of different food resources and selection of these resources by the Black rhino have not yet been documented. In order to enhance conservation of the Black rhino in the NCA, there is a need to carry out an assessment of the past rhino population trends, and current food resources availability and selection by this globally threatened rhino species. This study therefore sought to fill these knowledge gaps.

Study objectives
Broad objective
To fill biological knowledge for effective management and conservation for saving globally threaten species from extinction.

Specific objectives
i) To map the spatial distribution of the Black rhino population in the Ngorongoro Crater (NC),

ii) To assess selection of different forage species by Black rhino in the NC,

iii) To assess temporal trends in selected population attributes (size, growth rate, sex ratio and age-structure) in the NC during 2000-2014.

Research questions
i) How are the Black rhino individuals distributed within the Ngorongoro Crater?

ii) What plant species are preferred by the Black rhino?

iii) How has the Black rhino population changed over the past 15 years?

Justification of the study
By assessing the population dynamics, feeding ecology of the Black rhino and forage availability, this study provides information that could contribute towards enhanced conservation and management of this critically endangered rhino species and its habitat. Specifically, this information could be used by the Ngorongoro Conservation Area Authority (NCAA) to formulate policies, management strategies and interventions that enhance conservation of the Black rhino in the Ngorongoro Crater. In addition, the information generated could vitally inform strategies and policies aimed at bolstering conservation of Black rhino populations in Tanzania and beyond. Such information could be of value to government agencies, NGOs and the local communities and international community concerned with Black rhino conservation and management.

Scope of the study
This study was geographically limited to Ngorongoro Conservation Area (NCA) in Tanzania. NCA was purposely selected because it is one of the two places in Tanzania where the last populations of rhinos are found in their native habitats. Data was collected over a period of four months starting from mid-May to mid-June (wet season) and from mid-August to mid-September (dry season). The trends in population attributes were analyzed for a period of fifteen years from year 2000 to year 2014. The study focused only on the Black rhino sub-species Diceros bicornis michaeli, a sub-species categorized as Critically Endangered under IUCN, 2015 classification. Observations on foraging ecology were done early in the morning between 0630hrs to 09hrs and late in the afternoon between 1600hrs to 1800hrs when the rhino was expected to be actively feeding.

Limitations of the study
The study focused only on the relative frequencies of food availability and selection rather than the actual biomass. It was difficult to observe the rhino once they disappeared into the forest and thickets, making it difficult to document their activities in such places. In addition, observations could not be carried out at night, making it difficult to document their night-time feeding locations. Assessing the number of bites was also difficult when the plant is wholly consumed. It was not possible to detect plants that could have been wholly consumed or uprooted using the feeding site survey method employed in this study.

Assumptions of the study
The study assumed that the population under study was a closed population, with no immigration or emigration.

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