Michael Murray-Hudson

In arid and semi‐arid environments, many species use underground burrows for thermoregulation, reproduction, and to reduce predation risk. In Botswana, Temminck's ground pangolins ( Smutsia temminckii ) shelter in burrows during the day, and burrow density is thought to be a key indicator of habitat suitability for these animals. Pangolins are threatened by illegal trade and overexploitation, and individuals confiscated from the trade should be released in areas where they have the greatest chance of survival. To assist with the identification of suitable release sites, we quantified habitat‐specific burrow density and determined the effects of body size and sex on burrow selection. Burrow surveys were conducted in three sites, with detailed pangolin burrow selection data collected in two of those sites, in different landscapes in northern Botswana. Ten pangolins were fitted with telemetry transmitters between June 2022 and February 2024. Results indicate that habitat type was a stronger predictor of burrow density than soil type, with burrow density being higher in open than in woody habitats. Adult and female pangolins selected burrows with larger entrance diameters than sub‐adult and male individuals, respectively. Burrows in shrubland and tree savanna habitats were preferred, dry floodplains were avoided, and burrows in grassland and riparian woodland habitats were utilised in proportion to their availability; these selection patterns were not affected by body size, sex, or origin. The limited sample size, short study duration, and high rate of transmitter loss limit generalisation of results to the broader pangolin population, but the results indicate that suitable release sites for confiscated pangolins in Botswana may be in shrubland and tree savanna habitats.

Rewilding captive animals is an important strategy for rehabilitating individuals and ecosystems. Comparing the behaviors of released animals to their wild counterparts enables the evaluation of their adaptive response to new environments, assuming that wild animals are better suited to natural conditions. We examined how movement patterns of captive African savannah elephants ( Loxodonta africana ) before and after soft release compared with movement patterns of other elephant groups, rehabilitated and wild elephants, in the western Okavango Delta, Botswana. We monitored 12 adult female elephants using GPS collars: six captive elephants, subjected to a three‐year phased soft release, two elephants released more than a decade earlier and four wild elephants. We quantified 30‐min diurnal and nocturnal distances, cumulative daily distances, daily displacement, and monthly home range sizes across seasonal flood cycles. We analyzed the effects of release, season, time of day, and elephant group on movement metrics, comparing captive elephants before and after release, and with rehabilitated and wild elephants. Before release, captive elephants moved longer diurnal and shorter nocturnal 30‐min distances, covered longer cumulative daily distances, and occupied smaller home ranges. After release, these metrics shifted, reducing differences with rehabilitated and wild elephants, although captive elephant home ranges remained significantly smaller. This suggests that captive elephants changed their movement patterns post‐release in response to environmental cues. However, even the movement patterns of rehabilitated elephants were not completely similar to those of wild elephants, likely due to sample size, individual variation, or effects of prior taming. These results highlight the critical importance of long‐term monitoring of animals since the movement patterns of released animals may take several years to converge with those of wild counterparts.

Land use change threatens the integrity of riparian woodland vegetation. The aim of this study was to investigate the diversity and population structure of riparian plant species in protected and communal areas. A total of 71 transects were sampled from each of the protected and communal areas. Total species richness recorded was 36 and 38 in communal and protected areas, respectively. Species diversity was significantly (p < 0.05) higher in the protected than communal areas. Vachellia tortilis (communal areas) and Croton megalobotrys (both areas) showed a reverse J shaped pattern with more individuals in the lower diameter size classes than in the large ones. Dichrostachys cinerea (both areas), Ziziphus mucronata (communal areas), Combretum imberbe (protected areas), C. hereroense (protected areas), Berchemia discolor (protected areas) and Vachellia erioloba (communal areas) showed a reverse-J distribution pattern, but with missing size classes. Philenoptera violacea (protected areas) was characterized by a bell-shaped distribution with more individuals in the middle size classes than in the lower and upper ones while Combretum hereroense, C. imberbe and B. discolor were characterized by irregular population structure in communal areas. Croton megalobotrys, D. cinerea, C. imberbe, C. hereroense, Z. mucronata, B. discolor and S. erubescens had higher Important Value Indices (IVIs) in protected than communal areas. Comparatively, Vachellia tortilis, P. violacea and V. erioloba had higher IVIs in communal than protected areas. We recommended that species with J-shaped population structure and those with only one size class be protected to enable them to attain healthy population structures.

In southern Africa, the Okavango Delta is a large alluvial fan sustaining a unique wetlands ecosystem in the heart of the Kalahari desert. The Delta is fed by an annual flood that brings water from the Angolan plateaus to the north, down to the Okavango region. The fan is characterized by vegetated, permanent or seasonal floodplains, dotted with thousands of sandy islands of various origin (inverted paleo‐channels, paleo‐dunes, meander bars, etc). On at least some of these islands, shallow groundwater is characterized by a high pH (>8) and a high concentration of metals and metalloids, making it naturally toxic. In the 1990s, McCarthy and co‐workers explain the chemistry of that water through an evapotranspiration model, the flood‐water being pumped by the vegetation toward the center of the islands and progressively enriched in elements by evapotranspiration. This model has been widely applied to all islands in the Okavango, not considering their individual specificities nor that of the surrounding floodplain. Our work, based on a multidisciplinary approach including sedimentology, mineralogy and geochemistry, and discussed by McCarthy and Humphries, questions the established model suggesting that the alkaline water cannot derive from simple concentration of the floodwater.

The southward propagation of the East African Rift System inside the Southern African Plateau generates the Okavango Graben, hosting the Okavango Delta, which is one of the largest African endoreic ecosystems associated with an alluvial fan. The deformation and kinematics governing this propagation are still currently being debated, especially whether a strike-slip component is present and whether its impact on the dynamics of ecosystem was ever considered. To go further, we analysed the ground deformation from a network of semi-permanent GNSS stations located inside and around the Okavango Delta. As estimated from previous works, the Okavango Graben is submitted to a right-lateral displacement with highest strain along one border of the graben, where most of the seismicity is located. The inner floor displays a clockwise rotation generating local low intensity compression. This deformation pattern agrees with the asymmetric 3D shape of the basin. The ground subsides with higher rates in the north-east, generating a regional tilt that explains the progressive shift of the annual flood toward the north-east, as described in previous works. This tilting causes some areas to dry up and other areas to become almost permanently flooded. Therefore, we hypothesize that tectonic driving is responsible for the eastward migration of water which could then result in its capture by the Linyanti and Zambezi rivers. The long-term consequence of this deformation is the disappearance of the endorheism of the alluvial fan. This drastic hydrological change will disrupt the ecosystem and impact biodiversity as well as economic resources.

Freshwater organisms in the Okavango Delta and Lake Ngami (Botswana) provide direct and indirect benefits to people and the economy of the region. However, their existence could be potentially threatened by human activities (primarily, upstream water abstraction and planned hydropower structures) coupled with climate change. For their protection, it is essential to know their distribution, ecology, and status of the ecosystems that they inhabit. Publications that record taxa from the Delta at species level are scarce, particularly aquatic macroinvertebrates. Identifying organisms to species level can provide more accurate information for environmental monitoring and conservation programmes but requires significant training and expertise. Here, we present a comprehensive taxonomical review of 2204 freshwater species from the Okavango Delta and Lake Ngami, with additional 355 species found in other areas of Botswana that are likely to be present in the study region. We also compare the diversity of the Okavango Delta and Lake Ngami with two other tropical wetlands: the Pantanal (Brazil) and the Kakadu Region (Australia). We show that biodiversity in the Okavango Delta and Lake Ngami is higher than in previous estimates, with recorded species richness dominated by phytoplankton and macroinvertebrates. Most species are widespread across the system and southern Africa. The resulting database includes new records (Bryozoa, Porifera), information on species conservation status, habitat, ecology, distribution in continental Africa, site details and taxonomical notes. This will be an essential resource for researchers, conservation managers, policy makers and consultants investigating freshwater biodiversity in tropical wetlands in the region.

The Okavango Delta in North Botswana is a hot‐spot of biodiversity within the semi‐arid central part of the South African plateau. This endorheic ecosystem is highly dependent on the annual flood that brings freshwater from the highlands of Angola to the North. However, in many places, the groundwater of the Delta is saline and contains very high concentrations of metal and metalloid elements, making it toxic to the flora and fauna. These saline waters have been largely studied and their formation is generally explained through evaporation and evapotranspiration processes. However, no studies have investigated the geochemical composition of the sediments that host the aquifers. Here, we provide a complete sedimentological and geochemical investigation (major, traces and rare earth elements, carbon and oxygen stable isotopes ratios, Sr and Nd isotope ratios) of the various geomorphological and ecological compartments that form the landscape of the SW Okavango Delta. We demonstrate that the non‐connected underground aquifer is capped by a clay layer corresponding to a major event of dust deposition from the Makgadikgadi pan. We suggest that this aquifer may extend outside the island, below the floodplain and that the hydrological structure of the Nxaraga area is indeed composed of two non‐connected aquifers of different origins. Challenging the model based on evaporation and evapotranspiration, we propose that the composition of that allochtonous clay and the in situ reactions between sediment, water and organic matter in a confined aquifer explain the geochemical enrichment of the water.

Tropical wetlands are a significant source of atmospheric methane (CH₄), but their importance to the global CH₄ budget is uncertain due to a paucity of direct observations. Net wetland emissions result from complex interactions and co-variation between microbial production and oxidation in the soil, and transport to the atmosphere. Here we show that phenology is the overarching control of net CH₄ emissions to the atmosphere from a permanent, vegetated tropical swamp in the Okavango Delta, Botswana, and we find that vegetative processes modulate net CH₄ emissions at sub-daily to inter-annual timescales. Without considering the role played by papyrus on regulating the efflux of CH₄ to the atmosphere, the annual budget for the entire Okavango Delta, would be under- or over-estimated by a factor of two. Our measurements demonstrate the importance of including vegetative processes such as phenological cycles into wetlands emission budgets of CH₄.

The Okavango Delta in northern Botswana is an endorheic ecosystem formed by 150,000 islands surrounded by a flood plain. The vegetation of these islands displays an external tree ring enclosing a barren interior domain with evaporitic deposits. We sampled the groundwater into piezometers across an island at the southwest of the Delta, and drilled sediments. The geochemical analysis of the water exhibits two different compositions: a fresh water in the floodplain and a saline water in the interior part. These inner samples display enrichments in heavy metals, metalloids and critical metals such as, Rare Earth Elements (REE). The latest show a continuous enrichment from LREE to HREE and positive Ce and Eu anomalies, associated to alkaline pH. Overall, the two types of displayed REE patterns fingerprint two different water sources. The geochemistry of sediments indicates the same composition whatever the sample location and no traces of evaporitic deposits was found. The variations in the water table depth in the piezometers shows different hydrological behaviors in between the floodplain and the barren zone which does not follow the flood cycle. Thus, we document two different aquifers with independent hydrological behaviors: a surface fresh‐water aquifer in the floodplain connected to the channels, and a saline confined aquifer below the islands. The contrasted geochemical composition of the waters explains the distribution of the vegetation which survives through access to fresh water. The hydrological architecture of this island in the southwestern Delta differs from other islands, highlighting the hydrological complexity of the Okavango Delta.