Rhino Population Research Articles

Assessing Habitat Suitability: The Case of Black Rhino in the Ngorongoro Conservation Area

Efforts to identify suitable habitat for wildlife conservation are crucial for safeguarding biodiversity, facilitating management, and promoting sustainable coexistence between wildlife and communities. Our study focuses on identifying potential black rhino (Diceros bicornis) habitat within the Ngorongoro Conservation Area (NCA), Tanzania, across wet and dry seasons. To achieve this, we used remote sensing data with and without field data. We employed a comprehensive approach integrating Sentinel-2 and PlanetScope images, vegetation indices, and human activity data. We employed machine learning recursive feature elimination (RFE) and random forest (RF) algorithms to identify the most relevant features that contribute to habitat suitability prediction. Approximately 36% of the NCA is suitable for black rhinos throughout the year; however, there are seasonal shifts in habitat suitability. Anthropogenic factors increase land degradation and limit habitat suitability, but this depends on the season. This study found a higher influence of human-related factors during the wet season, with suitable habitat covering 53.6% of the NCA. In the dry season, browse availability decreases and rhinos are forced to become less selective of the areas where they move to fulfil their nutritional requirements, with anthropogenic pressures becoming less important. Furthermore, our study identified specific areas within the NCA that consistently offer suitable habitat across wet and dry seasons. These areas, situated between Olmoti and the Crater, exhibit minimal disturbance from human activities, presenting favourable conditions for rhinos. Although the Oldupai Gorge only has small suitable patches, it used to sustain a large population of rhinos in the 1960s. Land cover changes seem to have decreased the suitability of the Gorge. This study highlights the importance of combining field data with remotely sensed data. Remote sensing-based assessments rely on the importance of vegetation covers as a proxy for habitat and often overlook crucial field variables such as shelter or breeding locations. Overall, our study sheds light on the imperative of identifying suitable habitat for black rhinos within the NCA and underscores the urgency of intensified conservation efforts. Our findings underscore the need for adaptive conservation strategies to reverse land degradation and safeguard black rhino populations in this dynamic multiple land-use landscape as environmental and anthropogenic pressures evolve.

52,000 years of woolly rhinoceros population dynamics reveal extinction mechanisms

The extinction of the woolly rhinoceros (Coelodonta antiquitatis) at the onset of the Holocene remains an enigma, with conflicting evidence regarding its cause and spatiotemporal dynamics. This partly reflects challenges in determining demographic responses of late Quaternary megafauna to climatic and anthropogenic causal drivers with available genetic and paleontological techniques. Here, we show that elucidating mechanisms of ancient extinctions can benefit from a detailed understanding of fine-scale metapopulation dynamics, operating over many millennia. Using an abundant fossil record, ancient DNA, and high-resolution simulation models, we untangle the ecological mechanisms and causal drivers that are likely to have been integral in the decline and later extinction of the woolly rhinoceros. Our 52,000-y reconstruction of distribution-wide metapopulation dynamics supports a pathway to extinction that began long before the Holocene, when the combination of cooling temperatures and low but sustained hunting by humans trapped woolly rhinoceroses in suboptimal habitats along the southern edge of their range. Modeling indicates that this ecological trap intensified after the end of the last ice age, preventing colonization of newly formed suitable habitats, weakening stabilizing metapopulation processes, triggering the extinction of the woolly rhinoceros in the early Holocene. Our findings suggest that fragmentation and resultant metapopulation dynamics should be explicitly considered in explanations of late Quaternary megafauna extinctions, sending a clarion call to the fragility of the remaining large-bodied grazers restricted to disjunct fragments of poor-quality habitat due to anthropogenic environmental change.

GUT MICROBIOME DIVERSITY OF THREE RHINOCEROS SPECIES IN EUROPEAN ZOOS.

The wild rhinoceros populations have declined drastically in the past decades because the rhinoceros are heavily hunted for their horns. Zoological institutions aim to conserve rhinoceros populations in captivity, but one of the challenges of ex situ conservation is to provide food sources that resemble those available in the wild. Considering that the mammalian gut microbiota is a pivotal player in their host's health, the gut microbiota of rhinoceros may also play a role in the bioavailability of nutrients. Therefore, this study aims to characterize the fecal microbiome composition of grazing white rhinoceros (WR; Ceratotherium simum) and greater one-horned rhinoceros (GOHR; Rhinoceros unicornis) as well as the browsing black rhinoceros (BR; Diceros bicornis) kept in European zoos. Over the course of 1 yr, 166 fecal samples in total were collected from 9 BR (n = 39), 10 GOHR (n = 56), and 14 WR (n = 71) from 23 zoological institutions. The bacterial composition in the samples was determined using 16S rRNA gene Illumina sequencing. The fecal microbiomes of rhinoceros clustered by species, with BR clustering more distantly from GOHR and WR. Furthermore, the data report clustering of rhinoceros microbiota according to individual rhinoceros and institutional origin, showing that zoological institutions play a significant role in shaping the gut microbiome of rhinoceros species. In addition, BR exhibit a relatively higher microbial diversity than GOHR and WR. BR seem more susceptible to microbial gut changes and appear to have a more diverse microbiome composition among individuals than GOHR and WR. These data expand on the role of gut microbes and can provide baseline data for continued efforts in rhinoceros conservation and health status.

Genetic load and viability of a future restored northern white rhino population.

As biodiversity loss outpaces recovery, conservationists are increasingly turning to novel tools for preventing extinction, including cloning and invitro gametogenesis of biobanked cells. However, restoration of populations can be hindered by low genetic diversity and deleterious genetic load. The persistence of the northern white rhino (Ceratotherium simum cottoni) now depends on the cryopreserved cells of 12 individuals. These banked genomes have higher genetic diversity than southern white rhinos (C. s. simum), a sister subspecies that successfully recovered from a severe bottleneck, but the potential impact of genetic load is unknown. We estimated how demographic history has shaped genome-wide genetic load in nine northern and 13 southern white rhinos. The bottleneck left southern white rhinos with more fixed and homozygous deleterious alleles and longer runs of homozygosity, whereas northern white rhinos retained more deleterious alleles masked in heterozygosity. To gauge the impact of genetic load on the fitness of a northern white rhino population restored from biobanked cells, we simulated recovery using fitness of southern white rhinos as a benchmark for a viable population. Unlike traditional restoration, cell-derived founders can be reintroduced in subsequent generations to boost lost genetic diversity and relieve inbreeding. In simulations with repeated reintroduction of founders into a restored population, the fitness cost of genetic load remained lower than that borne by southern white rhinos. Without reintroductions, rapid growth of the restored population (>20-30% per generation) would be needed to maintain comparable fitness. Our results suggest that inbreeding depression from genetic load is not necessarily a barrier to recovery of the northern white rhino and demonstrate how restoration from biobanked cells relieves some constraints of conventional restoration from a limited founder pool. Established conservation methods that protect healthy populations will remain paramount, but emerging technologies hold promise to bolster these tools to combat the extinction crisis.

Antemortem detection of Mycobacterium bovis in nasal swabs from African rhinoceros

Mycobacterium bovis (M. bovis) infection has been identified in black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros populations in Kruger National Park, South Africa. However, it is unknown whether M. bovis infected rhinoceros, like humans and cattle, can shed mycobacteria in respiratory secretions. Limited studies have suggested that rhinoceros with subclinical M. bovis infection may present minimal risk for transmission. However, recent advances that have improved detection of Mycobacterium tuberculosis complex (MTBC) members in paucibacillary samples warranted further investigation of rhinoceros secretions. In this pilot study, nasal swab samples from 75 rhinoceros with defined infection status based on M. bovis antigen-specific interferon gamma release assay (IGRA) results were analysed by GeneXpert MTB/RIF Ultra, BACTEC MGIT and TiKa–MGIT culture. Following culture, speciation was done using targeted PCRs followed by Sanger sequencing for mycobacterial species identification, and a region of difference (RD) 4 PCR. Using these techniques, MTBC was detected in secretions from 14/64 IGRA positive rhinoceros, with viable M. bovis having been isolated in 11 cases, but not in any IGRA negative rhinoceros (n = 11). This finding suggests the possibility that MTBC/M. bovis-infected rhinoceros may be a source of infection for other susceptible animals sharing the environment.

Exploring temperature and precipitation changes under future climate change scenarios for black and white rhinoceros populations in Southern Africa

ABSTRACT Climate change is a potential human-induced threat to rhino populations and their habitat. Information on the effects of climate change on rhinoceros species can help manage and develop conservation plans to adapt to these changes. In this study, two climate change scenarios were used to predict temperature and precipitation changes in national parks in southern Africa and the effect those changes would have on black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros populations. The study used the Intergovernmental Panel on Climate Change (IPCC) Representative Concentration Pathways (RCPs) 4.5 and 8.5, atmospheric CO2 concentrations of 650 and 1370 ppm, for the years 2055 and 2085 to explore the temperature and precipitation changes. All spatial information was processed using Geographic Information Systems and statistical analysis. Results show the changing climate will have significant negative impacts on the probability of occurrence of both species. Temperature changes will affect these probabilities more than precipitation changes. All study parks will have zero probability of occurrence for the species throughout their ranges should conditions reach those represented by the RCP 8.5 scenario late in the century. Conservation activities for the rhinoceros should take into consideration the potential for temperature and precipitation changes modelled in this study.

Sperm collection in rhinoceros via urethral catheterization

Assisted reproductive technologies are playing an ever-increasing role in the management of ex situ rhinoceros populations. Traditionally, sperm collection in rhinos is conducted via electroejaculation (EEJ) or gamete rescue. Sperm collection via urethral catheterization (UC) is gaining popularity in wildlife reproductive sciences as it requires less specialized equipment, is faster, and less stimulatory than EEJ. This study investigated the use of UC to collect sperm from Southern white (Ceratotherium simum simum; n = 3) and Eastern black (Diceros bicornis michaeli; n = 6) rhinoceros as an alternative or complementary to collection via EEJ. UC samples (n = 14) exhibited high sperm concentration (1.6 ± 0.49 ×109 sperm/mL) and low volume (0.98 ± 0.26 mL). Samples obtained via EEJ (n = 11) were of moderate sperm concentration (0.14 ± 0.05 ×109 sperm/mL) and high volume (30.6 ± 7.2 mL). UC samples were processed for cryopreservation in OptiXcell extender. Motility of UC sperm decreased post-thaw (56 ± 2.4%) over pre-freeze (77.1 ± 3.2%; P < 0.05), with longevity data consistent to prior results published for sperm collected via EEJ. These results suggest sperm quality and cryo-survival are not impacted by the collection method. Since EEJ was conducted after UC, sperm parameters could not be compared between the two methods. Results indicate that UC is a viable alternative to EEJ for sperm collection in rhinoceros.

Bringing the Black rhino back: Key factors for reintroduction success

Evaluating reintroduction success is fundamental to wildlife management and conservation. Movement affects animal fitness and survival and is the first response of reintroduced animals, making it an excellent indicator of reintroduction success. However, there is limited information on the early post-release movement of reintroduced animals. Here, we addressed this important issue by studying the post-release behaviour of the critically endangered black rhinoceros, Diceros bicornis minor, reintroduced to the Gonarezhou National Park, Zimbabwe, in 2021. We used daytime sighting data collected from 21 rhinoceros for 1.5 years to investigate survival and reproduction, movement patterns and habitat selection after release. We examine how sex, age and different release sites affect the short-term movement behaviour and habitat selection of black rhinos. Rhinos showed progressive and consistent changes in movement patterns and habitat selection, shifting from large-scale movements during the early stages of release to smaller-scale movements after home ranges were established. We found that rhinos released in the large area had larger activity areas with less overlap between individuals and moved further away from the release site (less fidelity to the release site) than the individuals released in the smaller area. These findings confirm the great capacity of black rhinos to adapt to the environment, occupying large ranges when given the opportunity, but populations with smaller ranges can also be viable. Based on our study and a literature review, we stress the importance of long-term monitoring and believe that reserve size, rhino density, fencing, food and water availability, familiarity between conspecifics and human disturbance are key factors in the successful establishment of a rhino population that should be considered in future reintroductions. Finally, the high survival and birth rates in the first 1.5 years after reintroduction, together with most rhinos having established their home range, suggest a successful reintroduction in the short term.

Behaviour and habitat preferences of translocated rhinos (Rhinoceros unicornis) at Manas National Park, Assam, India

Manas National Park (MNP) is located in the foothills of the Himalayas along the border between India and Bhutan. The original greater one-horned rhino population (Rhinoceros unicornis) of the Park was annihilated in the year 2000 by poaching. Less than a decade later, a new rhino population was reintroduced with the support of Indian Rhino Vision 2020, as part of a wider programme that included infrastructure improvements, anti-poaching schemes, and other management interventions. Between 2008 and 2021, 22 rhinos were translocated to MNP from Kaziranga National Park (KNP) and Pobitora Wildlife Sanctuary (PWS). Post-release monitoring was carried out over a six-year period, from 2008–2013, during which 10 animals (three adult males, four adult females, and three calves) were monitored continuously, using radio telemetry to track collared animals, and direct observation to monitor their behaviour. The study period yielded 4,941 radio-tracked locations and 3,711 observations, which provided sex/age specific seasonal data on activity patterns, home ranges, association patterns, habitat preferences, and ‘stray incidents’ when animals wandered outside the Park boundaries. Some differences from behaviour patterns observed in high flood-risk areas such as KNP and PWS were attributable to MNP’s slightly higher elevation that protects rhinos from annual river floods. Overall, however, the translocated rhinos did not exhibit significant differences in their behaviour and ranging patterns compared to wild rhino populations documented in previous studies. This suggests that the translocated rhinos were able to adapt effectively to their new environment. The first calf was born to a translocated adult female in 2011 and, by 2022, the population of rhinos in MNP was estimated at 50 individuals, including 38 calves born following the reintroduction. This study demonstrates the potential of well-managed translocation schemes to contribute to the recovery of endangered rhinos.

White rhino ecology: a comparison of two rhino populations (Ceratotherium simum simum) in South Africa and Uganda

White rhino ecology: a comparison of two rhino populations (Ceratotherium simum simum) in South Africa and Uganda

Empire, Nature and Agrarian World: A History of Rhino Preservation in the Kaziranga Game Reserve, India (1902–1938)

The greater one-horned rhinoceros or Indian rhinoceros ( Rhinoceros unicornis ) faced extinction in British India at the end of the nineteenth century. In 1908, the Government of Assam established the Kaziranga Game Reserve (KGR, now Kaziranga National Park) to preserve the vanishing rhino. As the twentieth century progressed, creating wilderness – by demonising the presence of the peasants and graziers – became a global panacea for protecting wildlife. Contrary to that belief, this article will show how the rhino population revived amidst human existence dictated by agro-ecological interactions and bureaucratic expediencies. The rhino’s ethology and its place in the imagination of rural people minimised its enemies. Moreover, in fluvial geography that constantly transformed the KGR’s boundaries, peasants and graziers creatively negotiated their usufruct rights and supported rhino preservation. Locating the KGR in the historical analysis of fluvial agro-ecology, this study illuminates how a critical interaction between different actors, i.e. human and non-human and coloniser and colonised, accentuated the cultural and material contestations amidst which the rhino eventually survived.

Predicting Sex in White Rhinoceroses: A Statistical Model for Conservation Management.

Ensuring the effective management of every rhinoceros population is crucial for securing a future for the species, especially considering the escalating global threat of poaching and the challenges faced in captive breeding programs for this endangered species. Steroid hormones play pivotal roles in regulating diverse biological processes, making fecal hormonal determinations a valuable non-invasive tool for monitoring adrenal and gonadal endocrinologies and assessing reproductive status, particularly in endangered species. The purpose of this study was to develop a statistical model for predicting the sex of white rhinoceroses using hormonal determinations obtained from a single fecal sample. To achieve this, 562 fecal samples from 15 individuals of the Ceratotherium simum species were collected, and enzyme immunoassays were conducted to determine the concentrations of fecal cortisol, progesterone, estrone, and testosterone metabolites. The biological validation of the method provided an impressive accuracy rate of nearly 80% in predicting the sex of hypothetically unknown white rhinoceroses. Implementing this statistical model for sex identification in white rhinoceroses would yield significant benefits, including a better understanding of the structure and dynamics of wild populations. Additionally, it would enhance conservation management efforts aimed at protecting this endangered species. By utilizing this innovative approach, we can contribute to the preservation and long-term survival of white rhinoceros populations.

Probabilistic assessment of the risk of black rhinoceros (Diceros bicornis) species extinction

AbstractThe black rhinoceros (Diceros bicornis), distinguished by its distinctive horned snout and imposing size, stands perilously close to the precipice of extinction. The survival of this majestic species is threatened by a combination of factors, necessitating urgent scientific inquiry into the underlying causes. In this research article, a nonlinear stochastic Ricker model is employed to investigate the challenges faced by the population of black rhinoceros. By integrating innovative mathematical approaches with ecological understanding, the aim is to unravel the intricate dynamics contributing to the endangered status of the black rhino. The critical role of habitat loss and illicit poaching activities in driving the decline of this remarkable species is highlighted by the analysis. These findings emphasise the need for immediate and decisive action to protect the black rhinoceros and mitigate the risk of its extinction. It is imperative that comprehensive conservation efforts be implemented to ensure the long‐term survival of the black rhinoceros and preserve its invaluable place within the ecosystem.

Historical development of the survivorship of zoo rhinoceroses-A comparative historical analysis.

Zoo animal husbandry is a skill that should be developing constantly. In theory, this should lead to an improvement of zoo animal survivorship over time. Additionally, it has been suggested that species that are at a comparatively higher risk of extinction in their natural habitats (in situ) might also be more difficult to keep under zoo conditions (ex situ). Here, we assessed these questions for three zoo-managed rhinoceros species with different extinction risk status allocated by the IUCN: the "critically endangered" black rhino (Diceros bicornis), the "vulnerable" greater one-horned (GOH) rhino (Rhinoceros unicornis), and the "near threatened" white rhino (Ceratotherium simum). Comparing zoo animals ≥1 year of age, the black rhino had the lowest and the white rhino the highest survivorship, in congruence with their extinction risk status. Historically, the survivorship of both black and white rhino in zoos improved significantly over time, whereas that of GOH rhino stagnated. Juvenile mortality was generally low and decreased even further in black and white rhinos over time. Together with the development of population pyramids, this shows increasing competence of the global zoo community to sustain all three species. Compared to the continuously expanding zoo population of GOH and white rhinos, the zoo-managed black rhino population has stagnated in numbers in recent years. Zoos do not only contribute to conservation by propagating ex situ populations, but also by increasing species-specific husbandry skills. We recommend detailed research to understand specific factors responsible for the stagnation but also the general improvement of survivorship of zoo-managed rhinos.

Reductions in home-range size and social interactions among dehorned black rhinoceroses (Diceros bicornis)

Poaching for horns and tusks is driving declines of megaherbivores worldwide, including the critically endangered African black rhinoceros (Diceros bicornis). By proactively dehorning entire rhinoceros populations, conservationists aim to deter poaching and prevent species loss. However, such conservation interventions may have hidden and underestimated effects on animals' behavior and ecology. Here, we combine >15 y of black rhino-monitoring data across 10 South African game reserves, comprising >24,000 sightings of 368 individuals, to determine the consequences of dehorning for black rhino space use and social interactions. While preventative dehorning at these reserves coincided with a nationwide decrease in black rhino mortality from poaching and did not infer increased natural mortality, dehorned black rhinos decreased their home range area by, on average, 11.7 km2 (45.5%) and were 37% less likely to engage in social encounters. We conclude that dehorning black rhinos as an antipoaching measure alters their behavioral ecology, although the potential population-level effects of these changes remain to be determined.

Exploration of Invasive Alien Plant Species on Habitat of Rhino in Icharni, Chitwan National Park, Nepal

The study was conducted with main purpose to assess the floral diversity and explore invasive species on rhinoceros habitat in two different research sites with in Chitwan National Park. The rhino is placed in the list of endangered species by International Union for Conservation of Nature and highly threatened due to loss their habitat by rapidly increasing invasive species. The study was done for a period of one month in (September to October) 2020. The 10 m, 5 m, and 1 m radius circular quadrates were utilized to gather data on trees, shrubs, and herbs, respectively. A total of 25 plant species were recorded from 15 plots. The importance values of each species of trees were analyzed. Seven species of invasive types were recoded from 15 plots (10 plots from riverine forest and 5 plots from grassland). Mikania micrantha was most dominant species with IVI 103.02 followed by Pogostemon benghalensis with IVI 78.93 and Chromolaena odorata with IVI 34.57 as the second and third most dominant invasive species respectively. The conclusion is that invasive species have an impact on the grassland and riverine forest, which are needed by the mega herbivore. The management of rhino habitat and the preservation of the rhino population are seriously threatened.

Effects of age, seasonality, and reproductive status on the gut microbiome of Southern White Rhinoceros (Ceratotherium simum simum) at the North Carolina zoo

BackgroundManaged southern white rhinoceros (Ceratotherium simum simum) serve as assurance populations for wild conspecifics threatened by poaching and other anthropocentric effects, though many managed populations experience subfertility and reproductive failure. Gut microbiome and host health are inextricably linked, and reproductive outcomes in managed southern white rhinoceros may be mediated in part by their diet and gut microbial diversity. Thus, understanding microbial dynamics within managed populations may help improve conservation efforts. We characterized the taxonomic composition of the gut microbiome in the managed population of female southern white rhinoceros (n = 8) at the North Carolina Zoo and investigated the effects of seasonality (summer vs. winter) and age classes (juveniles (n = 2; 0–2 years), subadults (n = 2; 3–7 years), and adults (n = 4; >7 years)) on microbial richness and community structure. Collection of a fecal sample was attempted for each individual once per month from July-September 2020 and January-March 2021 resulting in a total of 41 samples analyzed. Microbial DNA was extracted and sequenced using the V3-V4 region of the 16S rRNA bacterial gene. Total operational taxonomic units (OTUs), alpha diversity (species richness, Shannon diversity), and beta diversity (Bray-Curtis dissimilarity, linear discriminant analysis effect size) indices were examined, and differentially enriched taxa were identified.ResultsThere were differences (p < 0.05) in alpha and beta diversity indices across individuals, age groups, and sampling months. Subadult females had higher levels of Shannon diversity (Wilcoxon, p < 0.05) compared to adult females and harbored a community cluster distinct from both juveniles and adults. Samples collected during winter months (January-March 2021) possessed higher species richness and statistically distinct communities compared to summer months (July-September 2020) (PERMANOVA, p < 0.05). Reproductively active (n = 2) and currently nonreproductive adult females (n = 2) harbored differentially enriched taxa, with the gut microbiome of nonreproductive females significantly enriched (p = 0.001) in unclassified members of Mobiluncus, a genus which possesses species associated with poor reproductive outcomes in other animal species when identified in the cervicovaginal microbiome.ConclusionTogether, our results increase the understanding of age and season related microbial variation in southern white rhinoceros at the North Carolina Zoo and have identified a potential microbial biomarker for reproductive concern within managed female southern white rhinoceros.

Conservation Innovations and Future Directions for the Study of Rhinoceros Gut Microbiome

Rhinoceros are among the largest and most endangered herbivores in the world. Three of the five extant species are critically endangered, with poaching and habitat loss contributing heavily to declines. The gut microbiome is an essential facet of host health and digestion, mediating a variety of immune and physiological functions. Certain microbes have the potential to serve as biomarkers for reproductive outcomes and predictors of disease susceptibility. Therefore, assessing gut microbial dynamics in relation to wild and managed rhinoceros populations has particular relevance for zoos and other conservation organizations that maintain assurance populations of these charismatic megafauna. The functional gut microbiomes associated with all rhinoceros species remain poorly studied, and many published reports are limited by small sample sizes and sex biases. In this review, we synthesize current research to examine the rhinoceros gut microbiome under human management and resulting conservation implications, address common pitfalls of wildlife gut microbiome studies, and propose future avenues of research in this field.

Population parameters, performance and insights into factors influencing the reproduction of the black rhinoceros Diceros bicornis in Namibia

AbstractEstimating the population parameters, performance and factors that influence reproduction from long-term, individual-based monitoring data is the gold standard for effective wildlife management and conservation. Yet this information is often difficult and costly to collect or inaccessible to managers. We synthesized a 20-year set of individual-based monitoring data from a subset of black rhinoceros Diceros bicornis subpopulations across a range of environmental conditions in Namibia. Our findings demonstrate that despite the relatively arid landscape in Namibia, the black rhinoceros metapopulation is performing well, measured by age at first reproduction, inter-birth interval, population growth and survivorship. Information-theoretic modelling revealed that a univariate model including normalized differential vegetative index had a greater influence upon age at first reproduction than population density. The inter-birth interval model set identified cumulative rainfall during the 15 months prior to the birth month as the top model, although the mean normalized differential vegetative index during the inter-birth interval was comparable. There was little evidence for density-dependence effects on reproduction. These findings suggest that although browse quality could have a greater impact on parameters spanning multiple years, shorter-term parameters could be more influenced by rainfall. Our analysis also revealed a synchronous pattern of conceptions occurring in the rainy season. Our study provides a set of population parameter estimates for Namibian black rhinoceros subpopulations and preliminary insights on factors driving their reproduction. These expand our collective knowledge of global black rhinoceros population dynamics and improve our confidence and capability to adaptively manage the black rhinoceros metapopulation of Namibia.

Exploring the behaviors and social preferences of a large, multigenerational herd of zoo-housed southern white rhinoceros (Ceratotherium simum simum).

The zoo-housed southern white rhinoceros (SWR) population is of special concern due to their lack of consistent breeding success. An enhanced understanding of SWR social preferences could better inform management planning by promoting natural social relationships, which can positively affect their well-being. The large, multigeneration herd housed at the North Carolina Zoo provides an ideal opportunity to examine rhino sociality across different ages, kin types, and social groupings. Eight female rhinos' social and nonsocial behaviors were recorded from November 2020 through June 2021 across 242 h. Activity budget analyses revealed strong seasonal and temporal variations in grazing and resting behaviors, with no stereotypic behaviors recorded. Bond strength calculations suggested that each female maintained strong social bonds with one to two partners. Beyond mother-nursing calf bonds, we found that the strongest social ties were maintained between calf-less adults and subadults in these dyads. Considering these findings, we recommend that management plans attempt to house immature females with calf-less adult females, as they may be necessary to the social landscape of immature females and, ultimately, improve their welfare.