Northern Botswana Research Articles

On the Right Track? Comparing Concurrent Spoor and Camera-Trap Surveys in Botswana

A diverse range of techniques have been used to survey mammals. Spoor counts and camera trapping are increasingly common survey tools used to detect the presence of species of interest in an area (occupancy). Given the significant time and financial investments in such surveys, and the management decisions based on their conclusions, it is imperative that confidence can be assigned to the results. It is therefore important to increase our understanding of the accuracy and constraints of each technique to allow managers and researchers to select the most suitable method for each situation. Here we compare results collected simultaneously using spoor and camera-trap surveys at a human—wildlife interface in northern Botswana. While our spoor survey and camera-trap surveys detected a similar number of mammal species (17 and 15, respectively), the species detected by each method differed. Of the 21 species detected overall, only about half (52.4%) were detected by both methods, and these co-detected species ha...

The Croton megalobotrys Müll Arg. traditional medicine in HIV/AIDS management: Documentation of patient use, in vitro activation of latent HIV-1 provirus, and isolation of active phorbol esters

Ethnopharmacological relevanceCurrent HIV therapies do not act on latent cellular HIV reservoirs; hence they are not curative. While experimental latency reversal agents (LRAs) can promote HIV expression in these cells, thereby exposing them to immune recognition, existing LRAs exhibit limited clinical efficacy and high toxicity. We previously described a traditional 3-step medicinal plant regimen used for HIV/AIDS management in Northern Botswana that inhibits HIV replication in vitro. Here we describe use of one component of the regimen that additionally contains novel phorbol esters possessing HIV latency-reversal properties. Aim of the studyWe sought to document experiences of traditional medicine users, assess the ability of traditional medicine components to reverse HIV latency in vitro, and identify pure compounds that conferred these activities. Materials and methodsExperiences of two HIV-positive traditional medicine users (patients) were documented using qualitative interview techniques. Latency reversal activity was assessed using a cell-based model (J-Lat, clone 9.2). Crude plant extracts were fractionated by open column chromatography and reverse-phase HPLC. Compound structures were elucidated using NMR spectroscopy and mass spectrometry. ResultsPatients using the 3-step regimen reported improved health over several years despite no reported use of standard HIV therapies. Crude extracts from Croton megalobotrys Müll Arg. (“Mukungulu”), the third component of the 3-step regimen, induced HIV expression in J-lat cells to levels comparable to the known LRA prostratin. Co-incubation with known LRAs and pharmacological inhibitors indicated that the active agent(s) in C. megalobotrys were likely to be protein kinase C (PKC) activator(s). Consistent with these results, two novel phorbol esters (Namushen 1 and 2) were isolated as abundant components of C. megalobotrys and were sufficient to confer HIV latency reversal in vitro. ConclusionWe have identified novel LRAs of the phorbol ester class from a medicinal plant used in HIV/AIDS management. These data, combined with self-reported health effects and previously-described in vitro anti-HIV activities of this traditional 3-step regimen, support the utility of longitudinal observational studies of patients undergoing this regimen to quantify its effects on plasma viral loads and HIV reservoir size in vivo.

Determining baselines for human-elephant conflict: A matter of time.

Elephant crop raiding is one of the most relevant forms of human-elephant conflict (HEC) in Africa. Northern Botswana holds the largest population of African elephants in the world, and in the eastern Okavango Panhandle, 16,000 people share and compete for resources with more than 11,000 elephants. Hence, it is not surprising this area represents a HEC ‘hotspot’ in the region. Crop-raiding impacts lead to negative perceptions of elephants by local communities, which can strongly undermine conservation efforts. Therefore, assessing trends in conflict levels is essential to developing successful management strategies. In this context, we investigated the trend in the number of reported raiding incidents as one of the indicators of the level of HEC, and assessed its relationship to trends in human and elephant population size, as well as land-use in the study area. For each of these factors, we considered data spanning historical (since the 1970s) and contemporary (2008–2015) time frames, with the aim of comparing subsequent inferences on the drivers of crop raiding and predictions for the future. We find that the level of reported crop raiding by elephants in the eastern Panhandle appears to have decreased since 2008, which seems to be related to the reduction in agricultural land allocated to people in recent years, more than with human and elephant population size. We show that inferences regarding the drivers of HEC and predictions for the future are dependent on the time span of the data used. Although our study represents a first step in developing a HEC baseline in the eastern Panhandle, it highlights the need for additional multi-scale analyses that consider progress in conservation conflict to better understand and predict drivers of HEC in the region.

Measuring human–wildlife conflicts: Comparing insights from different monitoring approaches

ABSTRACTStudies investigating wildlife crop‐damage have been widely documented, but methods often vary and results can be difficult to compare across national and international regions. Standardized data‐collection protocols involving local communities are encouraged in wildlife management research to address this issue; however, it is not clear how data collected from such systems compare with government monitoring schemes. I established an independent monitoring program for human–elephant conflict (HEC) incidents over a 3‐year period (2008–2010) in northern Botswana, following the International Union for Conservation of Nature (IUCN) data collection protocol. In addition, the government's monitoring scheme for problem‐animal control continued in the area. With these systems running simultaneously, I compared the data collection efficiency of the 2 approaches and explored implications of each on HEC management. The total number of crop‐damage incidents recorded differed between the 2 systems. The IUCN approach was temporally more efficient than the government approach, which influenced measurements of areas damaged by elephants. Government records showed a greater mean area of damage per elephant crop‐raiding incident compared with community enumerator records. A potential challenge of using the IUCN approach for wide‐scale HEC monitoring is the selection, cost, and management of enumerators. Ultimately, both approaches were effective for general monitoring of HEC incidents when the purpose of data collection was clearly defined. Monitoring systems that address broader issues beyond providing a record of damage incidents are likely to have a greater effect in reducing human–wildlife conflicts in the long‐term. © 2017 The Wildlife Society.

The vegetation and wildlife habitats of the Savuti-Mababe-Linyanti ecosystem, northern Botswana

This study classified the vegetation of the Savuti-Mababe-Linyanti ecosystem (SMLE), northern Botswana and developed a detailed map that provides a reliable habitat template of the SMLE for future wildlife habitat use studies. The major vegetation units of the SMLE were determined from satellite imagery and field visits and then mapped using Landsat 8 and RapidEye imagery and maximum likelihood classifier. These units were sampled using 40 m x 20 m (800 m²) plots in which the coverage of all plant species was estimated. Non-metric multidimensional scaling (NMS) demonstrated that plant communities were determined by gradients in soil texture or fertility and wetness. NMS 1 represented a gradient of soil texture with seven woodland communities on sandy soils (sandveld communities and Baikiaea forest) dominated by Baikiaea plurijuga in Baikiaea forest and Terminalia sericea and Philenoptera nelsii in sandveld, with various indicator species differentiating the various sandveld community types. Mopane woodland further from and riparian woodland adjacent to permanent water was common on less sandy alluvial soils. Mineral-rich, heavy clay soils in the sump of a large paleolake system support open grassland and mixed Senegalia/Vachellia (Acacia) savanna, with the mineral-rich soils supporting grasses high in minerals such as phosphorus, calcium, sodium and potassium, and thus this region is a critical wet season range for migratory zebra. Taller, high-quality grasses in the mosaic of sandveld and mopane woodland communities provide critical grazing for taller grass grazers such as buffalo, roan and sable antelope, whereas wetland communities provide reliable green forage during the dry season for a variety of herbivores, including elephant. This study has demonstrated how large-scale environmental gradients determine functional habitat heterogeneity for wildlife.Conservation implications: Our study demonstrated that the functionality of protected areas is determined by large-scale environmental gradients. Thus conservation science must aim to ensure that protected areas cover the full range of key environmental gradients in a region (soil texture and wetness in our study). Our habitat map provides a data base for wildlife habitat use studies in the region.

Ground survey of red lechwe in the Linyanti swamps and Chobe floodplains, northern Botswana

A ground survey of red lechwe was carried out in the Linyanti swamps and the Chobe floodplains of northern Botswana in the dry and wet seasons of 2012 and 2013, respectively. We documented numbers, sex ratio and age structure of red lechwe within the linear strips of 25 km × 300 m along the Linyanti swamps and the Chobe floodplains. Results indicated a significant difference in the numbers of red lechwe between sites and seasons. About 66 and 755 red lechwe were estimated for Chobe in the dry and wet season, respectively, with 343 and 261 of them estimated for Linyanti in the dry and wet season, respectively. In Chobe, the red lechwe densities varied widely between seasons (9 red lechwe/km2 – 101 red lechwe/km2 ) compared with Linyanti, where the densities did not vary much between seasons (35 red lechwe/km2 – 46 red lechwe/km2 ). The lower densities of red lechwe in Chobe in the dry season when compared with the wet season suggest a possible seasonal shift in the distribution of red lechwe to the nearby Zambezi floodplains in Namibia.Conservation implications: The higher number of red lechwe in the Chobe floodplains in the wet season indicates the potential of the floodplains as a habitat for this species in that season. The dry season shift in the distribution of red lechwe in Chobe presents an opportunity for local communities in Namibia to engage in tourism, whereas the return of the red lechwe to the floodplains in the wet season ensures protection of the animals as well as boosts the tourism potential of the Chobe National Park.

Seasonal habitat selection by African buffalo <i>Syncerus caffer</i> in the Savuti–Mababe–Linyanti ecosystem of northern Botswana

This study aimed to establish seasonal movement and habitat selection patterns of African buffalo Syncerus caffer in relation to a detailed habitat map and according to seasonal changes in forage quality and quantity in the Savuti–Mababe–Linyanti ecosystem (Botswana). Two buffalo were collared in November 2011 and another in October 2012. All three buffalo had greater activities in the mopane–sandveld woodland mosaic during the wet season, which provided high-quality leafy grasses and ephemeral water for drinking, but moved to permanent water and reliable forage of various wetlands (swamps and floodplains) and riverine woodlands during the dry season. Wetlands had higher grass greenness, height and biomass than woodlands during the dry season. Buffalo had similar wet season concentration areas in the 2011–2012 and 2012–2013 wet seasons and similar dry season concentration areas over the 2012 and 2013 dry seasons. However, their dry season location of collaring in 2011 differed dramatically from their 2012 and 2013 dry season concentration areas, possibly because of the exceptionally high flood levels in 2011, which reduced accessibility to their usual dry season concentration areas. The study demonstrates that extremely large and heterogeneous landscapes are needed to conserve buffalo in sandy, dystrophic ecosystems with variable rainfall.Conservation implications: This study emphasises the importance of large spatial scale available for movement, which enables adaptation to changing conditions between years and seasons.

Conservation implications of brown hyaena (<i>Parahyaena brunnea</i>) population densities and distribution across landscapes in Botswana

The brown hyaena (Parahyaena brunnea) is endemic to southern Africa. The largest population of this near-threatened species occurs in Botswana, but limited data were available to assess distribution and density. Our objectives were to use a stratified approach to collate available data and to collect more data to assess brown hyaena distribution and density across land uses in Botswana. We conducted surveys using track counts, camera traps and questionnaires and collated our results and available data to estimate the brown hyaena population based on the stratification of Botswana for large carnivores. Brown hyaenas occur over 533 050 km² (92%) of Botswana. Our density estimates ranged from 0 brown hyaenas/100 km² in strata of northern Botswana to 2.94 (2.16–3.71) brown hyaenas/100 km² in the southern stratum of the Central Kalahari Game Reserve. We made assumptions regarding densities in strata that lacked data, using the best references available. We estimated the brown hyaena population in Botswana as 4642 (3133–5993) animals, with 6.8% of the population in the Northern Conservation Zone, 73.1% in the Southern Conservation Zone, 2.0% in the smaller conservation zones and 18.1% in the agricultural zones. The similar densities of brown hyaenas in the Central Kalahari Game Reserve and the Ghanzi farms highlight the potential of agricultural areas in Botswana to conserve this species. The conservation of brown hyaenas in the agricultural landscape of Botswana is critical for the long-term conservation of the species; these areas provide important links between populations in South Africa, Namibia and Zimbabwe.Conservation implications: Botswana contains the core of the brown hyaena population in southern Africa, and conflict mitigation on agricultural land is crucial to maintaining connectivity among the range countries.

Carnivore distributions in Botswana are shaped by resource availability and intraguild species

AbstractThe composition of ecological communities is shaped by the interplay between interspecific interactions and species’ habitat and food requirements. The influence of interspecific interactions is particularly widespread within carnivore guilds, where species must balance the trade‐off between resource acquisition and potentially costly encounters with intraguild competitors/predators. We tested whether intraguild species activity or resource availability had a stronger influence on the seasonal distributions of 10 carnivore species in northern Botswana. We deployed 132 camera stations across a 330 km2 area during the 2014 dry season and 2015 wet season. For each species and season, we developed occupancy models based on resource availability (i.e. prey, vegetation and water) and on intraguild species (i.e. photographic detection rates of intraguild competitors and predators). We then used k‐fold cross‐validation to assess the relative predictive ability of each model. Carnivore distributions were generally negatively associated with dense vegetation and contrary to expectations, positively associated with the detection rate of intraguild species. This suggests competitor/predator avoidance did not play a large role in influencing carnivore distributions in northern Botswana, a result that differs from other systems, and might be attributed to differences in habitat, carnivore densities, and prey availability. The predictive ability of our resource availability vs. intraguild species models differed between seasons and among species. Leopard distributions, for example, were best predicted by resource availability during the dry season and by the activity of intraguild species in the wet season. The majority of seasonal distributions were best predicted by intraguild species activity or a combination of both resource availability and intraguild species activity. As environments continually change, studies similar to ours are pertinent as they can be used to monitor distributions of wildlife communities and to better understand the relative importance of the diversity of ecological processes impacting wildlife communities.

Orebody geometry, fluid and metal sources of the Omitiomire Cu deposit in the Ekuja Dome of the Damara Belt in Namibia

The Omitiomire Cu deposit (resource of 137 Mt at 0.54% Cu) in the Ekuja Dome of the Damara Belt in Namibia is hosted by an anastomosing, low-angle Pan-African (ca. 520 Ma) shear zone system developed around an older (ca. 1100–1060 Ma), late Mesoproterozoic intrusive breccia between a suite of mafic rocks (originally lava flows) and later tonalitic gneisses. High-grade ore shoots preferentially formed along contacts between tectonically interleaved biotite-epidote-quartz-chalcocite schists and felsic gneisses, and are directly related to an increase in the number and cumulative thickness of thin, contact-parallel mineralized shear zones. Alteration and mineralization are associated with elevated concentrations of K2O, Cr, Rb, S, and Cu and a loss of Na2O, CaO, and MgO. Oxygen isotope fractionation for quartz-biotite, quartz-feldspar, and quartz-amphibole mineral pairs support equilibrium temperatures of between 500 and 650 °C during the fluid/rock interaction. Mineral separates from amphibole-biotite gneisses and mineralized schists have similar ranges in δ18O values of about 1.2 to 2 ‰ relative to VSMOW. Coexisting minerals are arranged in an order of increasing δ18O values from biotite, to epidote, amphibole, and quartz, suggesting that the Omitiomire Shear Zone was a rock-dominated system. Similarly, H-isotope results for mineral separates from biotite-epidote schists and amphibole gneisses do not show any reversals for D/H fractionations, with δD values of between −48 and −82 ‰, typical of metamorphic-magmatic rocks. The homogeneous and low δ34S values (−6.1 to −4.7 ‰ CDT) are compatible with a local redistribution of sulfur from magmatic rocks and interaction with sulfur derived from metamorphic fluids of metasedimentary origin. The relatively low fluid/rock ratios and elevated Cu values (>1500 ppm) from unaltered amphibolite point to a local redistribution of an earlier (late Mesoproterozoic) Keweenaw-type Cu mineralization into later Pan-African shear zones during the exhumation of the Ekuja Dome. The timing, polyphase evolution, and tectonic setting of the Omitiomire deposit show remarkable similarities with the large Cu deposits of the Domes Region in the adjoining Lufilian Arc of northern Zambia. This suggests the presence of a much larger, regionally significant Cu province extending from central Namibia, through northern Botswana, and into Zambia.

Iron and nutrient content of wind-erodible sediment in the ephemeral river valleys of Namibia

Research concerning the global distribution of aeolian dust sources has principally focussed on salt/clay pan and desiccated lacustrine emission areas. In southern Africa such sources are identified as Etosha Pan in northern Namibia and Makgadikgadi Pans in northern Botswana. Dust emitting from ephemeral river valleys, however, has been largely overlooked. Rivers are known nutrient transport pathways and the flooding regimes of ephemeral river valleys frequently replenish stores of fine sediment which, on drying, can become susceptible to aeolian erosion. Such airborne sediment may be nutrient rich and thus be significant for the fertilisation of marine waters once deposited. This study investigates the dust source sediments from three ephemeral river valleys in Namibia in terms of their particle size distribution and their concentrations of bioavailable N, P and Fe. We compare the nutrient content of these sediments from the ephemeral river valleys to those collected from Etosha and Makgadikgadi Pans and consider their relative ocean fertilising potential. Our results show that the ephemeral river valleys contain fine grained sediment similar in physical character to Etosha and Makgadikgadi Pans yet they have up to 43 times greater concentrations of bioavailable iron and enriched N and P macronutrients that are each important for ocean fertilisation. The known dust-emitting river valleys of Namibia may therefore be contributing a greater fertilisation role in the adjacent marine system than previously considered, and not-yet investigated. Given this finding a re-assessment of the potential role of ephemeral river valleys in providing nutrient-rich sediment into the aeolian and marine systems in other dryland areas is necessary.

Effects of the safari hunting tourism ban on rural livelihoods and wildlife conservation in Northern Botswana

This paper examines the effects of the safari hunting ban of 2014 on rural livelihoods and wildlife conservation in Northern Botswana using the social exchange theory. The paper used both primary and secondary data sources. Data were analysed qualitatively. Results indicate that the ban led to a reduction of tourism benefits to local communities such as: income, employment opportunities, social services such as funeral insurance, scholarships and income required to make provision of housing for the needy and elderly. After the hunting ban, communities were forced to shifts from hunting to photographic tourism. Reduced tourism benefits have led to the development of negative attitudes by rural residents towards wildlife conservation and the increase in incidents of poaching in Northern Botswana. The implications of hunting ban suggest that policy shifts that affect wildlife conservation and rural livelihoods need to be informed by socio-economic and ecological research. This participatory and scientific approach to decision-making has the potential to contribute sustainability of livelihoods and wildlife conservation in Botswana.

Well-Being Impacts of Human-Elephant Conflict in Khumaga, Botswana: Exploring Visible and Hidden Dimensions

High densities of wild African savannah elephants (Loxodonta africana) combined with widespread human land-use have increased human-elephant conflict in northern Botswana. Visible impacts (e.g. crop/property damage, injury/fatality) of elephants on human well-being are well documented in scholarly literature while hidden impacts (e.g. emotional stress, restricted mobility) are less so. This research uses qualitative methods to explore human experiences with elephants and perceived impacts of elephants on human well-being. Findings reveal participants are concerned about food insecurity and associated visible impacts of elephant crop raids. Findings also reveal participants are concerned about reduced safety and restricted mobility as hidden impacts threatening livelihoods and everyday life. Both visible and hidden impacts of elephants contribute to people's negative feelings towards elephants, as does the broader political context. This research emphasises the importance of investigating both visible and hidden impacts of elephants on human well-being to foster holistic understanding of human-elephant conflict scenarios and to inform future mitigation strategies.

Living on the edge: characteristics of human–wildlife conflict in a traditional livestock community in Botswana

Context Conflicts between wildlife and humans have occurred for millennia, and are major drivers of wildlife decline. To promote coexistence, Botswana established buffer zones called wildlife-management areas (WMAs) adjacent to National Parks and Reserves where communities assume stewardship of wildlife and derive financial benefits from it. In contrast, communities outside WMAs are generally excluded from these benefits despite incurring ‘coexistence costs’, including crop damage and livestock depredation, although they may receive compensation for these losses. Aims To investigate the perceptions and actions of a livestock farming community outside (but surrounded by) WMAs in northern Botswana, especially in relation to predator management. Methods We conducted standard-format interviews with 62 heads of households (cattleposts), and evaluated responses using descriptive and multivariate statistics. Key results Almost half (46%) of respondents expressed negative perceptions of predators, with 67% reporting losses to predation. After disease, predation was the most commonly reported source of livestock losses. Increased age of the head of household was the strongest predictor of reported predation. Few households employed husbandry beyond kraaling at night, but some (21%) reported conducting lethal control of predators. Reported use of lethal control was independent of the household experience with predation and whether they derived financial benefits from wildlife. Instead, households with larger herds were more likely to report using lethal control, despite the most educated farmers tending to have larger herds. Lethal control was almost twice as likely in households previously denied government compensation for losses (42%) than in those granted compensation (23%). Perhaps as a result of perceived failures of the government compensation scheme, most households (91%) supported the development of an independent insurance program, with 67% expressing willingness to pay a premium. Conclusions Our results challenge the assumption that deriving financial benefit from wildlife increases tolerance. A measurable disconnect also exists between the willingness of a household to employ lethal control and their experience with predation, suggesting that lethal control was used pre-emptively rather than reactively. Implications Efforts must be made to connect the financial costs incurred during farming alongside wildlife with the financial benefits derived from wildlife. Where compensation schemes exist, timely payments may reduce retaliatory killing.

Trichodina diaptomi (Ciliophora: Peritrichia) from Two Calanoid Copepods from Botswana and South Africa, with Notes on its Life History

Members of the genus Trichodina are mostly found on fish, but have also been recorded from a variety of other aquatic organisms, including calanoid copepods. So far, it appears that all the trichodinid populations collected from calanoids in various parts of the world are the same species, i.e. Trichodina diaptomi Sramek-Husek, 1953. This paper reports on a new record of T. diaptomi from Metadiaptomus meridianus in a large reservoir in South Africa, as well as on a new host species, Metadiaptomus transvaalensis, and the first record of T. diaptomi from pools in an ephemeral river in northern Botswana, therefore adding a new country to the distribution of this species. We used the history of the discovery of T. diaptomi in different parts of the world and came to the conclusion that it is a cosmopolitan species, exclusively associated with copepods of the order Calanoida. Based on existing information, T. diaptomi does not appear to have a reservoir host. Against this background, we provide a discussion on the possibility that, although no dormant stage has been recorded for any trichodinid, it may be possible that T. diaptomi possesses some form of diapause and that this might be related to that of calanoid copepods.

Input, behaviour and distribution of multiple elements in abiotic matrices along a transect within the Okavango Delta, northern Botswana.

Wetlands fed by rivers can be a sink for elements depending on elemental concentrations, wetland hydrology, geochemistry, vegetation and climate. In the case of the Okavango Delta, northern Botswana, the outflow discharge is a small fraction (2-5%) of the inflow. This has strong potential consequences for the Delta, as it strongly affects element cycling and storage within the Delta. We estimated the inputs, behaviour and distribution of multiple elements along a longitudinal transect within the Okavango Delta, to show potential effects of retention mechanisms of different elements. High annual element input is rather attributed to discharge than to the concentration within the water, which is generally extremely low. We observed minimal enrichment of the elements within the water pathway along the transect from inflow to outlets, implying that element output is negligible. For most elements, we observed a high correlation between storage and sediment organic matter content. The organic matter content within the sediments was higher in the vegetated sediments than in non-vegetated sediments (factor∼10), and a similar trend was found for most elements. In conclusion, organic matter dominated in sediments from vegetated plots and thus plays an important role in retaining the elements within the sediments of the Delta. This finding has major implications for e.g. planning constructed wetlands for water purification or element retention especially in areas with high evapotranspiration.

Serosurvey for Selected Viral Pathogens among Sympatric Species of the African Large Predator Guild in Northern Botswana.

The recent increase in the creation of transboundary protected areas and wildlife corridors between them lends importance to information on pathogen prevalence and transmission among wildlife species that will become connected. One such initiative is the Kavango Zambezi Transfrontier Conservation Area of which Botswana's Okavango Delta constitutes a major contribution for wildlife and ecosystems. Between 2008 and 2011, we collected serum samples from 14 lions ( Panthera leo ), four leopards ( Panthera pardus ), 19 spotted hyenas ( Crocuta crocuta ), and six cheetahs ( Acinonyx jubatus ) in the Okavango. Samples were tested for antibodies against canine distemper virus (CDV), feline panleukopenia virus, enteric coronavirus, feline calicivirus, feline herpesvirus (FHV-1), and feline immunodeficiency virus (FIV). Evidence of exposure to all of these pathogens was found, to varying degrees, in at least one of the species sampled. High antibody prevalence (>90%) was only found to FHV-1 and FIV in lions. Only hyenas (26%, 5/19) were positive for CDV antibody. Except for one case, all individuals displayed physical conditions consistent with normal health for ≥12 mo following sampling. Our results emphasize the need for a comprehensive, multispecies approach to disease monitoring and the development of coordinated management strategies for subpopulations likely to be connected in transboundary initiatives.

Testing the Accuracy of Aerial Surveys for Large Mammals: An Experiment with African Savanna Elephants (Loxodonta africana).

Accurate counts of animals are critical for prioritizing conservation efforts. Past research, however, suggests that observers on aerial surveys may fail to detect all individuals of the target species present in the survey area. Such errors could bias population estimates low and confound trend estimation. We used two approaches to assess the accuracy of aerial surveys for African savanna elephants (Loxodonta africana) in northern Botswana. First, we used double-observer sampling, in which two observers make observations on the same herds, to estimate detectability of elephants and determine what variables affect it. Second, we compared total counts, a complete survey of the entire study area, against sample counts, in which only a portion of the study area is sampled. Total counts are often considered a complete census, so comparing total counts against sample counts can help to determine if sample counts are underestimating elephant numbers. We estimated that observers detected only 76% ± SE of 2% of elephant herds and 87 ± 1% of individual elephants present in survey strips. Detectability increased strongly with elephant herd size. Out of the four observers used in total, one observer had a lower detection probability than the other three, and detectability was higher in the rear row of seats than the front. The habitat immediately adjacent to animals also affected detectability, with detection more likely in more open habitats. Total counts were not statistically distinguishable from sample counts. Because, however, the double-observer samples revealed that observers missed 13% of elephants, we conclude that total counts may be undercounting elephants as well. These results suggest that elephant population estimates from both sample and total counts are biased low. Because factors such as observer and habitat affected detectability of elephants, comparisons of elephant populations across time or space may be confounded. We encourage survey teams to incorporate detectability analysis in all aerial surveys for mammals.

Size distribution of Baobabs on Kubu “Island”, Sowa Pan (northern Botswana): an indicator of late-stage evolution of the Makgadikgadi palaeo-lake and climate change?

We have investigated the size class distribution (SCD) of baobabs on a rocky outcrop, known alternatively as Kubu or Lekhubu, located in the southwest of Sowa Pan, northern Botswana. This study is aimed primarily at determining whether baobab girths show any systematic distribution relative to elevation, linked to palaeo-lake levels during the late Holocene. A secondary objective was to determine whether the SCD of the species might reflect late Holocene climatic changes. Our data show no systematic link between baobab size and elevation, and that the distribution of the species on the outcrop does not provide evidence for former levels of the palaeo-lake. Rather, the population structure is strongly influenced by large, old baobabs, which have provided localized long-lived seed centres favourable for sporadic germination and recruitment to the Kubu population. The broadly unimodal SCD of the Kubu baobab population does not appear to reflect climate changes over the lifespan of the species (up to ~1500 years). This is most likely linked to the development pattern of the species, with rapid growth over the first quarter to half of the tree’s life, followed by subsequent very slow growth rates.

Rift Valley fever vector diversity and impact of meteorological and environmental factors on Culex pipiens dynamics in the Okavango Delta, Botswana.

BackgroundIn Northern Botswana, rural communities, livestock, wildlife and large numbers of mosquitoes cohabitate around permanent waters of the Okavango Delta. As in other regions of sub-Saharan Africa, Rift Valley Fever (RVF) virus is known to circulate in that area among wild and domestic animals. However, the diversity and composition of potential RVF mosquito vectors in that area are unknown as well as the climatic and ecological drivers susceptible to affect their population dynamics.MethodsUsing net traps baited with carbon dioxide, monthly mosquito catches were implemented over four sites surrounding cattle corrals at the northwestern border of the Okavango Delta between 2011 and 2012. The collected mosquito species were identified and analysed for the presence of RVF virus by molecular methods. In addition, a mechanistic model was developed to assess the qualitative influence of meteorological and environmental factors such as temperature, rainfall and flooding levels, on the population dynamics of the most abundant species detected (Culex pipiens).ResultsMore than 25,000 mosquitoes from 32 different species were captured with an overabundance of Cx. pipiens (69,39 %), followed by Mansonia uniformis (20,67 %) and a very low detection of Aedes spp. (0.51 %). No RVF virus was detected in our mosquito pooled samples. The model fitted well the Cx. pipiens catching results (ρ = 0.94, P = 0.017). The spatial distribution of its abundance was well represented when using local rainfall and flooding measures (ρ = 1, P = 0.083). The global population dynamics were mainly influenced by temperature, but both rainfall and flooding presented a significant influence. The best and worst suitable periods for mosquito abundance were around March to May and June to October, respectively.ConclusionsOur study provides the first available data on the presence of potential RVF vectors that could contribute to the maintenance and dissemination of RVF virus in the Okavango Delta. Our model allowed us to understand the dynamics of Cx. pipiens, the most abundant vector identified in this area. Potential predictions of peaks in abundance of this vector could allow the identification of the most suitable periods for disease occurrence and provide recommendations for vectorial and disease surveillance and control strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1712-1) contains supplementary material, which is available to authorized users.