Population densities of eastern black rhinoceros : unravelling the controls

Key words: black rhinoceros, browser, corticosterone, diet, density dependence, minerals, moisture, physiological stress, savanna, soil nutrients, woody cover. Understanding the forces that cause variability in population sizes is a central theme in ecology. The limiting factor in populations of large mammals which are not controlled top‐down by predation is food, i.e., such populations are controlled by bottom‐up processes. However, there is little evidence of density dependence in large‐ to mega-herbivores. Yet, conservationists have managed Critically Endangered mega‐herbivores like rhinoceros as if their population growth were density dependent, i.e., following a logistic growth curve, focusing on large growth at population densities presumed to be at half‐carrying capacity (K/2). This would enable them to translocate animals at presumed half‐carrying capacity to retain local population densities and to create new populations in areas of suitable habitat, where animals are considered safe against poaching. This study focused on one such mega‐herbivore, the eastern black rhinoceros (Diceros bicornis michaeli) to re‐consider the density dependence population regulation in a mega‐herbivore and uses the findings to contribute to possible solutions towards conservation challenges facing this species. The expectations were that increases in population density would result in a decrease in reproductive performance, and that physiological stress levels in animals in populations of high density would be higher than in animals in populations of low densities. Nine populations of black rhinoceros across Kenya were studied, with variation in their respective densities, Plant Available Moisture (‘PAM’ i.e., ‘soil moisture’) and Plant Available Nutrients (‘PAN’ i.e., ‘soil fertility’). Data from available records (1993‐2010) were used to assess reproductive performance. Dietary quality and levels of corticosterone were estimated through faecal analysis from animals sampled in the field and from data on feeding trials of black rhinoceroses in zoos (dietary analysis only). Woody cover estimates were used to assess available browse for black rhinoceros. Two measures of density were used, i.e., absolute density (animals/km2) and relative density, i.e., absolute density as a ratio to the estimated maximum stocking density or ‘carrying capacity’. The effects of PAM and PAN, and subsets of PAM (rainfall and temperature) were incorporated and controlled in testing expectations. No evidence for density dependence was found. Reproductive performances tended to be better where PAM was high, PAN was low and woody cover was sparse. PAM was found to be directly correlated with quality of dietary browse. Black rhinoceros populations appeared controlled more by bottom‐up processes through key resources, even though their densities were perhaps too low to fully support this alternative view. It was apparent that the density dependence concept still requires more investigation. Deliberate efforts should be made to secure high PAM – low PAN – sparse woody cover areas for conservation of black rhinoceros. Conservation managers are advised to consider set percentage translocations, as opposed to the current translocation of black rhinoceros on the basis of an imaginary ‘carrying capacity’ and density dependence.</p

A proposed framework for short-, medium- and long-term responses by range and consumer States to curb poaching for African rhino horn

African rhinos are suffering a new poaching onslaught for their high-priced horns. Despite intensified anti- poaching activities, the number of rhinos poached per day has continued to increase since 2008. Between 2010 and 2011 more than 1.5% of the African rhino population was poached each year: a higher percentage is projected for 2012. This trend in increased poaching will reverse overall positive rhino population growth in the long term. In response, a rhino emergency summit comprising representatives of rhino range States, the private sector, government officials and non-governmental organizations met in Nairobi during April 2012. Following this meeting, we propose an integrated framework directed at reducing the demand-and-supply ratio associated with the use of rhino horn. The framework is envisaged to guide short- as well as medium- to long-term responses by range States directed at reducing the incentives for poaching and ensuring the persistence of rhinos

Census and ear-notching of black rhinos (Diceros bicornis michaeli) in Tsavo East National Park, Kenya

This paper updates the status of the black rhino population in Tsavo East National Park (NP). Data were acquired through aerial counts of the black rhino between 3 and 9 October 2010 using three fixed-wing husky aircrafts and a Bell 206L helicopter in an area of about 3,300 km2. Based on previous sightings of rhinos, the area was divided into 14 blocks, with each block subdivided into 400 m transects. An aircraft flying at about 500 m above the ground was assigned to carry out the aerial survey following these transects within each block. Observers scanned for rhinos about 200 m on either sides of the flight paths. Intensive searches in areas with dense vegetation, especially along the Galana and Voi Rivers and other known rhino range areas was also carried out by both the huskies and the helicopter. The count resulted in sighting of 11 black rhinos. Seven of these individuals were ear notched and fitted with radio transmitters and the horns were tipped off to discourage poaching. Three of the seven captured rhinos were among the 49 animals translocated to Tsavo East between 1993 and 1999. The other four animals were born in Tsavo East. Two female rhinos and their calves were not ear-notched or fitted with transmitters. It is recommended that another count be carried out immediately after the wet season as the rhinos spend more time in the open areas while the vegetation is still green. The repeat aerail count is to include blocks north of River Galana

Analysis of Electromagnetic Field Radiation from a Rectangular Cavity-Backed Slot Antenna Using ADI-FDTD Method

In this paper, a rectangular Cavity Backed Slot Antenna (CBSA) Model excited by a probe is investigated. The analysis is carried out using the Alternating Direction Implicit - Finite Difference Time Domain (ADI-FDTD) Method which is applied to investigate its characteristics in terms of radiation patterns and power. This is because the method is capable of providing a more accurate definition of the electromagnetic fields within the rectangular apertures, while eliminating the Courant-Friedrich-Levy (CFL) stability condition which is present in the regular Finite Difference Time Domain (FDTD) method. A cavity-backed slot antenna structure with dimensions of 14cm×22cm×30cm is analyzed with the slot and aperture measurements done at 3GHz. Results showing current distribution on the material surrounding the apertures are presented and a discussion on the physical aspects of the aperture radiation phenomenon is also presented. Keywords: cavity-backed slot antenna (CBSA), aperture radiation, alternating direction implicit-finite difference time domain (ADI-FDTD) metho

Density dependence and population dynamics of black rhinos (Diceros bicornis michaeli) in Kenya's rhino sanctuaries

Density-dependent feedback mechanisms provide insights into the population dynamics and interactions of large herbivores with their ecosystem. Sex ratio also has particularly important implications for growth rates of many large mammal populations through its influence on reproductive potential. Therefore, the interrelationships between density-dependent factors, comprising density, sex ratio and underlying growth rates (r) were examined for the Eastern black rhino (Diceros bicornis michaeli) living in three rhino sanctuaries in Kenya using four population models. The exponential and logistic models gave similar results and the former were accepted because they better portrayed the actual situation on the ground. Sex ratios in all sanctuary populations were positively correlated with r but interpreted with realization of other factors also affecting r. We caution that the results of population models should be interpreted alongside ground-truthed observations. We recommend that future translocation strategies should take into account sex and age structures of the donor population, while future studies of density dependence should take into account both biotic and abiotic factors

Sex-biased inbreeding effects on reproductive success and home range size of the critically endangered black rhinoceros

A central premise of conservation biology is that small populations suffer reduced viability through loss of genetic diversity and inbreeding. However, there is little evidence that variation in inbreeding impacts individual reproductive success within remnant populations of threatened taxa, largely due to problems associated with obtaining comprehensive pedigree information to estimate inbreeding. In the critically endangered black rhinoceros, a species that experienced severe demographic reductions, we used model selection to identify factors associated with variation in reproductive success (number of offspring). Factors examined as predictors of reproductive success were age, home range size, number of nearby mates, reserve location, and multilocus heterozygosity (a proxy for inbreeding). Multilocus heterozygosity predicted male reproductive success (p58%) and correlated with male home range size (p 44%). Such effects were not apparent in females, where reproductive success was determined by age (p <0.01, explained deviance 34%) as females raise calves alone and choose between, rather than compete for, mates. This first report of a 3-way association between an individual male's heterozygosity, reproductive output, and territory size in a large vertebrate is consistent with an asymmetry in the level of intrasexual competition and highlights the relevance of sex-biased inbreeding for the management of many conservation-priority species. Our results contrast with the idea that wild populations of threatened taxa may possess some inherent difference from most nonthreatened populations that necessitates the use of detailed pedigrees to study inbreeding effects. Despite substantial variance in male reproductive success, the increased fitness of more heterozygous males limits the loss of heterozygosity. Understanding how individual differences in genetic diversity mediate the outcome of intrasexual competition will be essential for effective management, particularly in enclosed populations, where individuals have restricted choice about home range location and where the reproductive impact of translocated animals will depend upon the background distribution in individual heterozygosity. © 2013 Society for Conservation Biology

Unusual mortalities of the eastern black rhinoceros (Diceros bicornis michaeli) due to clostridial enterotoxaemia in Ol Jogi Pyramid Sanctuary, Kenya

Nine eastern black rhinoceroses (Diceros bicornis michaeli) developed clinical clostridial enterotoxaemia between May and July 2010 in the Pyramid Black Rhino Sanctuary within the Ol Jogi Conservancy, Laikipia, Kenya. The rhinos presented with a peracute syndrome characterised by severe abdominal pain manifested by struggling and rolling on the ground, laboured breathing and died within three hours after being sighted sick. Necropsy and histopathology revealed severe pathology in the gastro-intestinal tract (GIT). Grossly, the small and large intestines were congested and oedematous. All the rhinos had variable amounts of hemorrhagic fluid in the intestines. Microscopically, the most characteristic lesion was severe necrotising-haemorrhagic enteritis. Numerous gram-positive rod-shaped bacterial colonies that were identified to be Clostridium spp were occasionally seen in the intestinal mucosa. Clostridium perfringens type A was isolated from the stomach contents. C. perfringens was postulated as the aetiological agent with the infection triggered probably by change of habitat following a prolonged period of drought that was followed by above normal rainfall

Trypanosomosis and other co-infections in translocated black (Diceros bicornis michaeli) and white (Ceratotherium simum simum) rhinoceroses in Kenya

Recent efforts towards the conservation of endangered rhinoceroses in Kenya include re-introduction of the animals into regions where they occurred previously. These efforts have however been hampered by mortalities of translocated animals. The current study was undertaken to determine the cause of deaths amongst black rhinoceroses (Diceros bicornis michaeli) and white rhinoceros (Ceratotherium simum simum), which were re-introduced into Meru National Park. Out of 28 translocated rhinoceroses, 7 (3 white and 4 black) (25%), died 3 months post translocation. At post-mortem, the carcasses of these animals were emaciated and heavily infested with ticks of different species. Further studies were conducted to determine the occurrence of hemoparasites in two sick black rhinoceroses and one white rhino. The density of tsetse flies and species of ticks present at the locality were also determined. The sick black rhinoceros were found to harbour mixed infections of T. congolense, T. simiae spp, and T. godfreyi, Theileria spp. and microfilaria. One of the sick black rhinos which never recovered presented very low packed cell volume and total protein levels. The tick species observed in all rhinos included Amblyomma, Rhipicephalus and Boophilus. The total number of Glossina pallidipes Austen and G.brevipalpis Newstead flies trapped per trap per day were 395 and 25, respectively. The tsetse density was considered very high and species distribution overlapped in the sanctuary. The study shows that the rhinos could have died from a co-infection of various haemoparasites. Control of tsetse flies should be implemented and its effectiveness regularly evaluated before and after translocation of rhinoceroses into areas known to be endemic for trypnaosomosis

Density dependence and population dynamics of black rhinos (Diceros bicornis michaeli) in Kenya's rhino sanctuaries

Density-dependent feedback mechanisms provide insights into the population dynamics and interactions of large herbivores with their ecosystem. Sex ratio also has particularly important implications for growth rates of many large mammal populations through its influence on reproductive potential. Therefore, the interrelationships between density-dependent factors, comprising density, sex ratio and underlying growth rates (r) were examined for the Eastern black rhino (Diceros bicornis michaeli) living in three rhino sanctuaries in Kenya using four population models. The exponential and logistic models gave similar results and the former were accepted because they better portrayed the actual situation on the ground. Sex ratios in all sanctuary populations were positively correlated with r but interpreted with realization of other factors also affecting r. We caution that the results of population models should be interpreted alongside ground-truthed observations. We recommend that future translocation strategies should take into account sex and age structures of the donor population, while future studies of density dependence should take into account both biotic and abiotic factors