**3. Population ecology of great one-horned rhinoceros in Dudhwa National Park after translocation**

When the remains of a newborn calf were found in tall grass after the reintroduction in August 1987, the sign of breeding was detected. The first successful calving occurred in 1989. Three more calves followed this in the same year. According to estimates, 58 rhino calves have been born and 35 rhinos (adults and calves) have died in the past 37 years.

**Figure 2.** *Rhino mother and calf feeding in the grassland of Dudhwa National Park.*

**Birth rate:** A total of 58 rhino calves were born between 1984 and 2021. The mean number of calves born per year is two calves per year. The population-specific crude birth rate is 0.17 per year for a number of adult females in the reproductive age class. The birth rate varied across the years with a higher birth rate at certain years followed by intermittent lower birth rates. This could be attributed to the number of females giving birth and the inter-calving interval duration (3–4 years) by adult females due to parental care.

**Mortality:** The mean mortality rate is 0.05/year for the rhino population in Dudhwa National Park. The mortality rate was higher during the initial period of the re-introduction of rhinos (0.4/year), and it was lower (0.2/year) in the subsequent years (**Figure 3**). The major causes of mortality were mal-–male aggression, predation by tigers, and natural causes. Similarly, the major causes of mortality (80%) in rhinos were reported to be self-fight, tiger predation, and poaching in Nepal [16]. Male aggression and fighting among males were more during the breeding time, associated with the territorial behavior of males [17]. Further, male mortalities are significantly higher than females [18]. Retaliatory killing of rhinos due to the human-rhino conflict in Nepal was also reported. An increase in the population and dispersal of rhinos outside the protected area could be the factors attributed to the human-rhino conflict in their distributional range.

**Population growth:** The rhino population growth data were modeled using the logistic growth model by non-linear least squares. The parameter values (*β1*) initial asymptote is 39.68, and the growth parameter value (*β<sup>2</sup>* is 0.12). The predicted curve is fitted with the actual population data (**Figure 4**), and the model was highly significant. The curve reached asymptote in the year 2010, and the population has been fluctuating near 35–40 individuals for the last 12 years. Further extension of the area or dispersal of individuals could enable the population size to increase.

*An Assessment of the Population Density of Greater One-Horned Rhinoceros in Uttar Pradesh… DOI: http://dx.doi.org/10.5772/intechopen.109824*

**Figure 3.**

*Birth rate/year/adult female and mortality rate of Indian rhinoceros across the years in Dudhwa National Park from 1984 to 2021.*

**Figure 4.** *Actual Indian rhinoceros population and predicted logistic model of population growth in Dudhwa National Park (1984–2021).*

#### **3.1 Age-specific survival rate**

The proportion of individual rhinos surviving at a particular age class was calculated based on the number of rhinos dying at the specific age class. The survivorship curve is similar to other mammal species with higher mortality at the very young age class followed by moderate mortality in the middle ages and higher mortality at the older age class. Male rhinoceros mortality tends to be higher in the younger age class and female mortality is higher in older individuals. The mortality rate for a very young individual is higher due to predation by tiger (1%). Earlier studies on rhinos reported gender-specific differences in mortality with higher mortality among male rhinos [19, 20]. Male mortality is higher in the dispersal age class. In most of the ungulate species, males die disproportionately due to enhanced growth rates, dispersal behavior, and intra-male aggression [21]. Injuries sustained during the male-male fight may cause mortality directly or indirectly [22]. Male Indian rhinoceros fight each other for territory or mates to establish dominance (**Figure 5**).

**Age-specific fecundity rate:** The average age at primiparity observed in Indian rhinoceros is five years. The gestation period is 15–16 months. It appears that the female rhinos remain fertile in old age; an adult female gave birth to her sixth calf at the age of 34 years. The fertility rate varied across ages, with a higher fertility rate at the age class between 8 and 20 years, with a mean fecundity rate of 0.24 and a maximum of 0.40. The fertility rate reduces as the female rhinos reach more than 25 years old. The Indian rhinoceros female produces 4–6 calves in their lifetime (**Figure 6**).

**Inter-birth interval:** The reported inter-calving interval is 3–4 years. The present observation on 10 adult females over 47 birth records indicated a minimum of 1.6–10 years of an inter-birth interval with an average of 4.3 years. Thus, in Indian rhinos, about 61% of births occurred during 3–5 years of interval. The inter-birth interval rate is higher than that of the African buffalo, which is reported to have 1–2 years [23]. Earlier studies in the study area on rhinos indicated that inter-birth interval was associated with the age of the mother [24]. It can be inferred from the earlier graph that the fecundity rate decreases with the age of the female rhinoceros (**Figure 7**).

**Figure 5.** *Age-specific survival rate of Indian rhinoceros in Dudhwa National Park (1984–2021; based on mortality record of male = 12; female = 15).*

*An Assessment of the Population Density of Greater One-Horned Rhinoceros in Uttar Pradesh… DOI: http://dx.doi.org/10.5772/intechopen.109824*

#### **Figure 6.**

*Age-specific fecundity rate of Indian rhinoceros in Dudhwa National Park (1984–2021; n = 10 adult females; over 47 birth records).*

**Figure 7.**

*Inter-birth interval duration of Indian rhinoceros in Dudhwa National Park (n = 10 adult females; over 47 birth records).*

### **4. Conclusions**

The Indian rhinoceros population has increased and reached asymptote in the year 2010, and the population has been fluctuating near 35–40 individuals for the past 12 years. Further extension of the area or dispersal of individuals could enable the population size to increase. The mean birth rate and mortality rate of rhinos in

Dudhwa National Park are 0.17/year/adult female and 0.05/year, respectively. Rhinos, in accordance with their large body size, exhibit life-history traits similar to other large mammal species with a slow onset of sexual maturity, fewer number of young ones produced, and higher inter-birth interval and remain fertile in old age. The survival rate of a female is higher than that of a male. The environmental and ecological factors such as carrying capacity, food availability, predation, and environmental stochasticity may influence the life-history traits of rhinos. The natural forest areas adjacent to the protected areas need to be maintained to enable the dispersal of the increasing population in Dudhwa National Park.
