Research

Introduction and Top Research Priorities

Largely due to the rhino poaching crisis that far out-weighs any other challenge facing rhinos today, the top five priorities of the Rhino Research Council, listed below, are skewed towards in situ issues. It is important to note that these research priorities are not ranked in order of importance, so the first and only priority focused on the ex situ population is not considered more important than the others. The Rhino Research Council realizes that conservation of genetic diversity via cell/gamete rescue from remnant populations is really not a research issue and is more of an implementation challenge, but it was identified as an important action to emphasize at this time of crisis. Following this list of the highest research priorities, the chapter continues with important areas of ex situ research, including reproduction, health, nutrition, behavior/ecology, and genetics. For more detailed discussions of in situ research needs, the reader is referred to the Rhino Research Council’s 2014 Rhino Research Masterplan.

 

Investigate Major Factors Affecting Health and Reproduction Ex Situ

• Epidemiology of browser rhino health issues—Health concerns and unusual syndromes continue to impact black rhinos in captivity, but the incidence of various conditions shifts over time, and patterns require constant monitoring and re-evaluation to track current trends and conditions. Otherwise, outdated problems and historic records continue to be referenced at the cost of realizing emerging trends and realities. One example is the significant increase in the number of black rhino deaths due to renal disease compared to five years ago and a decreased incidence of mortality due to hemolytic anemia compared to 20 years ago. It would be extremely useful to secure ongoing support for a point person whose priority is to evaluate the historical data and current situations to keep abreast of the problems and factors associated with those health issues.

• Iron overload syndrome (significance, detection, treatment, prevention)—Evidence that hemosiderosis is occurring in browsing rhinos is solid, but there are still many questions surrounding the impact of this condition on rhino health, whether it is primary or secondary, why it is occurring, and what can be done about it. In the past decade, relatively little progress has been made. Although there has been some progress in developing oral iron chelators for humans, the efficacy and safety of such medications are unknown in rhinos, and they are cost prohibitive. Research on dietary tannins as iron chelators has produced inconclusive results. Recent studies on the impact of large volume, regular phlebotomies for reducing iron marker values has shown promise but is unlikely to be adopted as a long-term management strategy at many institutions. Research in any of the four areas—cause, detection, prevention and treatment—could be valuable in producing insight on how to manage/prevent this condition.

• Obesity/body condition scoring—Overconditioning in captive rhinos can lead to a multitude of health problems, including musculoskeletal, foot, and reproductive problems. One example is the almost certain exacerbation of pododermatitis associated with captive husbandry conditions in the greater one-horned rhino. Research on standardizing body condition scores for all rhino species, along with improved nutritional management, should be a priority for captive health. 

• Sub-optimal reproduction (stillbirths, embryo loss, phytoestrogens, pathology)—Although reproductive success has improved in white and greater one-horned rhinos by changing management strategies, providing larger spaces and more complex social groups that include experienced and inexperienced individuals, and allowing mate choice options, there are a few reproductive challenges that remain unresolved and challenge our ability to develop self-sustaining populations. For example, < 50% of all captive white rhinos are reproductively successful, almost 50% of greater one-horned rhino calves are stillborn, and as our ability to evaluate larger numbers of female rhinos has improved, incidence of known embryo loss and reproductive pathology continue to increase.

​

Improve Rhino Identification and Monitoring 

• Optimize/standardize survey methodologies—Given the current poaching crisis, research that can improve our ability to monitor and survey wild populations is extremely important. Post-release monitoring is our primary method of determining the success of translocation, dehorning and many other conservation efforts. Data compiled from tracking individuals after translocation can be used to develop specific criteria that individual rhinos should meet (sex, age, reproductive status) prior to translocation in order to improve the success rate. Better methods for signal transduction and reception would be helpful for forest-dwelling animals. Creative methods of transmitter attachment are needed since horn transmitters are difficult to insert in de-horned animals, and radiocollars are a challenge given the neck morphology of rhinos. Also, lesions can occur with collars. Given the abundance of research on this topic in the military field, adaptation and application of this newer technology may be useful for rhinos. 

• Genetic census—Advances in genetic analyses of fecal samples, hair, environmental-DNA and microbiomes could be used to determine the genetic diversity among wild populations, including sex ratios, number of individuals and extent of inbreeding. Identify Most Important Factors in Translocation Success Translocations have proven extremely valuable in saving rhinos from poaching, re-populating parks/ranches, bolstering dwindling populations and establishing new populations. However, there is room for improvement, and given the importance of this action for long-term rhino survival, research is needed to enhance survival and reproductive success of every rhino moved. Studies might focus on the following example topics: white rhino boma maladaptation, mortality rates in different habitats, impacts of dehorning, impact on source populations, and identifying the type of individuals most likely to succeed.

​

Identify Most Important Factors in Translocation Success

Translocations have proven extremely valuable in saving rhinos from poaching, re-populating parks/ranches, bolstering dwindling populations and establishing new populations. However, there is room for improvement, and given the importance of this action for long-term rhino survival, research is needed to enhance survival and reproductive success of every rhino moved. Studies might focus on the following example topics: white rhino boma maladaptation, mortality rates in different habitats, impacts of dehorning, impact on source populations, and identifying the type of individuals most likely to succeed.

​

Determine Ecological Factors Impacting Rhino Populations

To choose the best locations for rhinos and provide guidance for those who want to improve their land in support of rhino populations, more information is required regarding specific ecological traits that impact rhino population survival and ability to thrive. Spatial ecology is especially important and is integrated with habitat quality, usage and preference.

​

Conserve Genetic Diversity via Cell/Gamete Rescue from Remnant Populations (small/sub-populations and highly endangered)

Given the poaching crisis in Africa and India and the rapid decline of Sumatran rhinos throughout their range, it seems prudent that every effort should be made to preserve cell lines and gametes from all genetically valuable rhinos/populations. The methodologies already exist but may need to be modified for the field conditions encountered in the African savannah and the tropical forests of Asia.

​

Areas in Need of Research Ex Situ Reproduction

Reproduction:

• It is still apparent based on studbook data that < 50% of the captive white rhino population has successfully reproduced. There are some young first-generation-captive-born (F1) animals that are not reproducing, but the problem is not solely with F1s. Results from several studies have demonstrated that many of the female F1s that fail to reproduce are exhibiting reproductive cycles, are behaving normally and are being mated by males. Therefore, interest has shifted towards examining post-copulatory events that may be causing infertility, such as inflammation, early embryo loss and/or developmental abnormalities potentially due to dietary phytoestrogens. However, there are still many adult white rhinos with irregular reproductive cycles (long ~70 day cycles versus normal ~35 day cycles), and with the increased use of ultrasonography for monitoring white rhino ovarian activity, it has been determined that some acyclic white rhinos are developing only small follicles that do not grow and mature into pre-ovulatory follicles. Fortunately, hormonal therapy has shown promise for these animals, although resumption of natural, regular cyclicity has not been restored following hormone treatment. High reproductive success at several facilities with large spaces and high numbers of white rhinos continue to support the long-held theory that management is the most significant factor impacting captive white rhino propagation. Interestingly, data from “wild” populations have also indicated that white rhinos at higher densities are more successful, and mating success is not fairly distributed. Some males are far more successful than others.

  • ​The following is a summary of the primary issues with white rhino reproduction:

    • F1 females are mating but not producing calves. 

    • White rhino estrogen receptors are more sensitive to phytoestrogens than those of greater one-horned rhinos. Is there a negative impact of dietary phytoestrogens on reproductive success? 

    • Irregular reproductive cycles (long versus short) are still occurring. 

    • Acyclic females appear to be producing small follicles that do not mature. Hormonal therapy shows some promise but, so far, has not restored regular, normal cyclicity, and more work is needed. 

    • Mate choice appears to be important in white rhinos since introducing new males often solves reproductive problems. How can we determine suitable mates before moving animals?

​

• Early embryonic death (EED)—Repeated documentation of EED in all captive rhino species is puzzling. In the past 15 to 20 years, there have been at least six confirmed cases of EED in white rhinos at four different institutions, five confirmed cases of EED in greater one-horned rhinos at three different locations, and seven EEDs confirmed in two Sumatran rhinos at two locations. Few rhinos are monitored closely enough to diagnose EED, so considering the number of confirmed cases, it appears to be a common occurrence in the captive population. It has also been reported in at least one field study in wild black rhinos. However, in most field studies females breed only once or twice before conceiving and carrying pregnancies to term, so the high incidence of EED in captivity seems aberrant. In addition to EED, abortions later in gestation have also been reported. There are many potential causes of EED and abortion in rhinos, including uterine infection, uterine scarring from a previous dystocia, endometrial hyperplasia, reproductive pathology, hormonal insufficiency, dietary insufficiency or toxicity, social/behavioral influence of enclosure co-inhabitants or other health-related conditions of the female rhinos. It is quite possible EED is occurring in many females that are breeding repeatedly without producing calves. Further investigation into the prevalence and potential causes of EED and abortion is warranted. 

​

• Reproductive pathology—Reproductive tract pathology in female rhinos has been reported in all captive rhino species and prevalence can be as high as 50% in females over 15 years of age (white rhinos). It can range from small, inconsequential cysts that do not affect fertility to large, invasive tumors that jeopardize the life of the rhino. There is general agreement that these pathologies typically develop in rhinos that spend the majority of their lives in a non-pregnant state and could be related to repeated exposure to hormone fluctuations, a condition not natural in wild rhinos that spend much of their time pregnant. However, there are some younger rhinos that also develop severe pathology, and more recent research has revealed that a fairly substantial proportion of white and greater one-horned rhinos develop pathologies in their early teens. Understanding the etiology of this pathology and identifying hormone therapies that might prevent it would be very useful. Furthermore, criteria for determining when the degree and types of pathology observed during an exam can be tolerated without loss of fertility versus those that render a female infertile would be very useful to establish so that appropriate management recommendations could be made. 

• Silent estrus—Behaviorally silent estrous cycles have now been documented in a few white rhinos. This phenomenon challenges efforts to breed this species in zoos because introductions often are made based on behavior. In white rhinos, silent estrus seems to be associated with the development of small follicles that do not reach pre-ovulatory size. When these white rhinos are treated with hormonal therapy, they do develop pre-ovulatory sized follicles and ovulate but still do not exhibit appropriate receptivity towards the male

​

• Measuring estrogen—Quantifying changes in estrogen levels that correlate with meaningful reproductive events has been difficult in several of the rhino species and continues to be challenging. A more accurate and meaningful way to assess estrogen concentrations could be useful for monitoring cyclicity, timing introductions and assessing other reproductive characteristics.