Updated: Oct 19
The Great one-horned Rhinoceros (Rhinoceros unicornis) was once spread all over the Indian subcontinent. It is the second-largest among the five extant species, of which the three are only two living female white rhinos making them functionally extinct. As a result of habitat destruction and hunting for its much-valued horn, there are as few as 2200 individuals left in the wild. These individuals are restricted to small forests of Assam, West Bengal, and southern Nepal. An adult male weighs up to 2100 kg and stands up to 186 cm at the shoulder, whereas adult females weigh about 1600 kg and are about 160 cm in height. They are characterized by the single nasal horn which is customarily between 15-45 cm long. One less known fact about rhinos is the presence of lower incisor tusks present in both males and females which can reach up to 15-45 cm in length. The molars and premolars are high crowned or hypsodont which aids them to grind the grass and cellulosic plants more effectively. The upper lip is prehensile which helps them to gather tall grass and shrubs. One fascinating fact about this prehensile lip is that it can be folded under and opposed against the lower lip for cropping short grasses. There are two folds of skin that encircle the whole body- one behind the forelegs and one in front of the hindlegs, that’s why the saying “thick-skinned like a rhino”. There are also deep skin folds around the neck which is most marked in males compared to females. A scent gland is also present on each foot.
A study conducted in the Chitwan National Park found that rhinos usually fancied tall grasses like of the Saccharum species. Other food included short grasses, sedges, submerged and floating aquatic plants, herbs, creepers, ferns, shrubs, and the leaves, twigs, and fruit of trees and saplings. However, the dieta shifts according to the season and spatial changes. Rhinos were also observed to consume planted crops of the agricultural lands during peak harvesting seasons which included maize and rice harvests. However, when herbs and grasses flourished in the fields during monsoon, it was preferred more than the harvested crops. The diet type develops with the season as well as with different vegetation types. A rhino might be expected to feed most productively in an area where its highly preferred food types are abundant. Thus, there is more correlation between utilization and preferability. It was observed in this study that tall grasses are most preferred during spring, short grasses during monsoon, and short grasses and shrubs during the winter.
Rhinos often lick and ate soil or rock materials. This is done to substitute for the minerals needed by the body which is not obtained in the needed quantity only from feeding on plants.
Courtesy: Save the Rhino
Rhinos are often seen wallowing in pools, rivers, lakes, etc. during the summer days. It was seldom observed during the winters. The most common type of group observed in one-horned rhino is the cow-calf pairs. Rhinos usually don’t move around in large groups but the highest observed were three individuals in one group in the Chitwan Valley. Temporary groups are seen while wallowing and feeding on large grounds. However, in these groups, the movement was independent of one another. Sometimes sub-adults can also be seen interacting, but interaction in adults is very minimum unless aggressive.
The largest and loudest repertoires of vocalization of the rhinos is in accord with it being solitary animal living in habitats of poor visibility.
Rhinos usually are heard communicating by 6 types of vocalizations-
• The snort is produced when a quick burst of air is released from the lips and the nostrils. It Is an initial contact call when meeting another rhino.
• The honk is a low-pitched guttural vocalization of echoing nature emitted as a single burst or in a succession of burst heard mostly during agnostic interaction. It is similar to the snort but is much more audible from a distance compared to a snort.
• Bleat is a single tone and loud vocalization typically uttered with head held low and mouth open. This usually signifies submission or flight.
• The roar is confined to a face to face interaction where the dominant rhino is seen using this vocalization while chasing away other rhinos.
• The other vocalizations are squeak-pant and moo-grunt.
The eyesight of the Indian rhinos is very poor. However, visual discriminatory between Black Rhinos and Indian Rhinos indicate that the latter has much better.
Rhinos usually show interest in the sites of urination and defecation of other rhinos by pausing and sniffing. Females squirted their urine behind only during estrous. However, adult males always urinated in a squirting fashion. They squirted the urine in the surrounding vegetation and hauled their hind toes in the earth and rubbing their head and horn in the surrounding low vegetation at the same time. Such displays are often seen in response to the sight and scent of other rhinos crossing a line feature, thereby marking its territory. Rhinos usually defecate on or near the dung of other rhinos. This is done to usually mark a route and is seen mostly near the edges of the forest, on the banks of the river or wallows, and paths or manmade roads and ditches.
If you want to read the end of this article, stay tuned for part two which is to be published next week (Sunday, 1pm)
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A. Laurie, "Behavioural ecology of the Greater one-horned rhinoceros (Rhinoceros unicornis)", Journal of Zoology, vol. 196, no. 3, pp. 307-341, 1981. Available: 10.1111/j.1469-7998.1982.tb03506.x [Accessed 3 October 2020].