The black rhinoceros (Diceros bicornis), an iconic species of East and Southern Africa, faces numerous threats, including poaching and habitat reduction, leading to its classification as critically endangered. While often referred to as "black," their colors range from brown to grey. The name "black rhinoceros" arose from a misinterpretation, distinguishing it from the "white rhinoceros" (Ceratotherium simum) based on lip shape rather than color. The black rhino has a pointed or hooked lip, while the white rhino has a square lip. This article delves into the dietary habits of the black rhinoceros, exploring its preferences, adaptations, and ecological role.
Black Rhinoceros Subspecies and Distribution
Historically, the black rhino's range encompassed much of southern and eastern Africa. Several subspecies have been identified, some of which are now extinct. These include:
- Southern black rhinoceros (D. b. bicornis): Extinct.
- North-eastern black rhinoceros (D. b. brucii): Extinct.
- Western black rhinoceros (D. b. longipes): Extinct.
- Chobe black rhinoceros (D. b. chobiensis): Restricted to the Chobe Valley.
- Uganda black rhinoceros (D. b. ladoensis): Conservation status is unclear.
- Eastern black rhinoceros (D. b. michaeli): Primarily found in Kenya, Rwanda, and Tanzania.
- South-central black rhinoceros (D. b. minor): The most widely distributed subspecies.
- South-western black rhinoceros (D. b. occidentalis): Restricted to wildlife reserves in Namibia.
Today, black rhinos are primarily found in protected nature reserves within Angola, Botswana, Eswatini, Kenya, Lesotho, Malawi, Mozambique, Namibia, South Africa, Tanzania, Zambia, and Zimbabwe. In May 2017, eighteen eastern black rhinos were moved from South Africa to Akagera National Park in Rwanda. In October 2017, the governments of Chad and South Africa reached an agreement to transfer six black rhinos from South Africa to Zakouma National Park in Chad.
Physical Characteristics and Adaptations
The black rhino is smaller than the white rhino, with adults possessing two horns, the anterior being larger. The longest known black rhinoceros horn measured nearly 1.5 m (4.9 ft) in length. These horns are used for defense, intimidation, digging up roots, and breaking branches during feeding. Black rhinos have thick-layered skin, which protects them from thorns and sharp grasses. The species overall is classified as critically endangered (even though the south-western black rhinoceros is classified as near threatened) and is threatened by multiple factors including poaching and habitat reduction.
Their eyesight is comparatively good, about the level of a rabbit. Their ears have a relatively wide rotational range to detect sounds.
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Dietary Preferences and Feeding Behavior
Black rhinos are herbivorous browsers, consuming leafy plants, twigs, branches, shoots, thorny wood bushes, small trees, legumes, fruit, and grass. Their diet can include up to 220 species of plants. They exhibit a preference for a few key plant species and tend to select leafy species in the dry season, with woody plants being favored during other times of the year. The black rhino's pointed and prehensile upper lip is perfectly adapted for grasping leaves and twigs when feeding. This prehensile lip allows them to grasp branches, hold foliage, and pick fruits with ease. Their bite produces a neat, angular mark on woody vegetation, similar to pruning shears.
Black rhinos follow the same trails that elephants use to get from foraging areas to water holes. They also use smaller trails when they are browsing.
Habitat and Foraging Patterns
The optimal habitat for black rhinos consists of thick scrub and bushland, often with some woodland. They browse for food in the morning and evening. In the hottest part of the day, they are most inactive, resting, sleeping, and wallowing in mud. Wallowing helps cool down body temperature during the day and protects against parasites.
Black rhinos live in bushlands, riverine woodlands, and marshes. Habitat preferences are shown in two ways: the amount of sign found in the different habitats, and the habitat content of home ranges and core areas. Habitat types are also identified based on the composition of dominant plant types in each area.
Nutritional Aspects
Zoo studies quantified hay intake of black rhinos at 1.1 % or 1.6 % of body mass (14 and 21 kg for grass and alfalfa hay, respectively), whereas animals consuming natural browses ate up to 30 kg (2.5% of body mass). The rhino stomach, containing high concentrations of lactate and low levels of volatile fatty acids (VFA), is a primary digestion site of soluble dietary carbohydrates (CHO = sugars), and fats.
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The crude fat content of rhino browses (2 to 24%) is considerably higher than found in most captive, dry diets ca. 2-3%, and may, in fact be the single most important nutrient group for this species. Lipogenesis in rhinos, as in other non-ruminants, probably relies heavily on glucose as a main substrate preferentially through the pentose phosphate shunt. If energy is limiting from imbalanced carbohydrate sources, lipogenesis could be impacted in rhinos.
Macromineral and trace element ranges in native rhino browses fall into general ranges for horse requirements. Sodium (Na) may be limiting in native browses, but can be readily obtained in natural salt licks. Phosphorus (P) appears to be limiting in natural rhino browses.
Plasma vitamin A (retinol) levels in free-ranging black rhinos are 10-fold lower than those seen in most other mammalian species, averaging 0.04 ? 0.01 to 0.06 ? 0.03 ig/ ml. Plasma vitamin E levels in free-ranging rhinos have been shown to differ among locations, ranging from 0.23 ? 0.07 ig/ml in Kenya to 0.80 ? 0.05 in Namibia.
Ecological Role
Black rhinos play a vital role in their ecosystems. As large vegetarians, rhinos eat up to 30 kilograms of plant matter per day. This helps shape the African landscape by reducing competition and keeping different species of plants in balance. The black rhino, and rhinoceroses in general, have been widely described as a keystone species, meaning those which hold a disproportionately significant role within an ecosystem. The most discernible service provided by the black rhino is the way in which the species shapes and maintains its surrounding landscape. Considering each individual black rhino consuming approximately 50 kilograms of vegetation per day, these incredible creatures control the overgrowth of plants and create pathways through dense shrubland to facilitate the migration of numerous species. The ensuing 20kg of dung deposited across the black rhino’s territorial range not only facilitates soil fertilisation and seed dispersal, but also provides sustenance to a range of animals. Dung beetles lay their eggs within balls of rhino faeces, which are then consumed by small animals such as mongooses once the beetle larvae develop. Additionally, black rhinos maintain symbiotic relationships with animals such as oxpeckers and terrapins, who feed on the ticks and parasites that inhabit any open wounds that the rhino might have.
Threats and Conservation
Black rhinos have been listed as critically endangered by the IUCN since 1996. The most urgent threats that black rhinos face are illegal poaching for their horns, habitat loss due to human intrusion, and climate change.
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Parks and reserves have been made for protecting the rhinos with armed guards keeping watch, but even still many poachers get through and harm the rhinos for their horns.
Conservation efforts include:
- Translocation of black rhino populations to enclosed sanctuaries and conservation areas.
- Providing training for guards, equipment for monitoring and surveillance.
- Developing DNA databases to analyze the DNA of intercepted rhino horns and linking them to the poached animal.
- Involving local communities in conservation efforts through education campaigns and by offering alternative sources of income.
- Education and awareness-raising campaigns to dispel myths regarding any healing properties associated with rhino horn.
Communication and Social Behavior
Black rhinos use several forms of communication. Due to their solitary nature, scent marking is often used to identify themselves to other black rhinos. Urine spraying occurs on trees and bushes, around water holes, and feeding areas. Defecation sometimes occurs in the same spot used by different black rhinos, such as around feeding stations and watering tracks.
Adults are solitary, coming together only for mating. Courtship behaviors before mating include snorting and sparring with the horns among males. The gestation period for a black rhino is 15 months. The mother and calf stay together for 2-3 years until the next calf is born.