Late Dry Season Research Articles

Intentions behind common and risky fires in south-eastern Tanzania

Human-set fires are a crucial component of African savannas, affecting ecosystem structure, carbon emissions, local hazards and livelihoods. Yet, most fire research in these ecosystems focuses on the fire ecology of protected areas. Research exploring fire regimes in inhabited landscapes remains limited, undermining opportunities for culturally and environmentally sustainable fire management. To address this gap, we used interviews in Tanzanian farming communities and remote sensing to identify intentions behind fire use and the perceived relative frequency and riskiness of fires set for different purposes. We found that the most common ignitions were intentional and important to livelihoods. Burning was adaptive, responsive to environmental conditions, and optimised for the intended outcome with the perceived riskiest fires intentionally spreading uncontrolled. Remote sensing showed that most of the total burned area was accounted for by fires during the late dry season when people burned for activities, such as field preparation, and when environmental conditions encouraged fire spread. Our findings offer an insight into fire regimes in inhabited landscapes, by exploring how intentions shape the fire regime at the landscape scale. We discuss how understanding these intentions and local priorities, including adaptive uses of fire, is key to sustainable fire management outside protected areas.

Woody cover change in relation to fire history and land-use in the savanna-woodlands of north-east Namibia (1996–2019)

Vegetation cover estimates for trees, shrub-grass mosaics, and grassland and bare ground, were quantified in the savanna-woodland of Bwabwata National Park, north-east Namibia. Changes in woody cover were analysed using repeat photographs in combination with aerial photographs and recent satellite imagery taken between 1996 and 2019. Cover estimates for each vegetation type were obtained using object-based classification techniques and a non-parametric random forest classifier algorithm in eCognition Trimble software. Results show that over the two decades under investigation (1996–2019), trees declined (−10.6%), and the shrub-grass mosaic vegetation type increased (8.1%) across the park. The largest decline in trees occurred in the western land use areas (−36%), which also experienced the greatest increase in the shrub-grass mosaic (17%), when compared with areas in the east (11%). Variation of woody cover estimates is attributed to different seasonal fire management practices in the east versus the west of the park. The fire history (2000–2018) revealed that late dry season fires were frequent in the west, whereas in the east, early dry season fires were frequent. The stages of encroachment recorded in this study have consequences for biodiversity, people’s livelihoods, and tourism.

Diet quality, liveweight change and responses to N supplements by cattle grazing

Experiments during 4 years examined the diets selected, growth, and responses to N supplements by Bos indicus-cross steers grazing summer-rainfall semi-arid C4 Astrebla spp. (Mitchell grass) rangelands at a site in north-western Queensland, Australia. Paddock groups of steers were not supplemented (T-NIL), or were fed a non-protein N (T-NPN) or a cottonseed meal (T-CSM) supplement. In Experiment 1, young and older steers were measured during the late dry season (LDS) and the rainy season (RS), while steers in Experiments 2–4 were measured through the annual cycle. Because of severe drought the measurements during Experiment 3 annual cycle were limited to T-NIL steers. Pasture availability and species composition were measured twice annually. Diet was measured at 1–2 week intervals using near infrared spectroscopy of faeces (F.NIRS). Annual rainfalls (1 July–30 June) were 42–68% of the long-term average (471 mm), and the seasonal break ranged from 17 December to 3 March. There was wide variation in pasture, diet (crude protein (CP), DM digestibility (DMD), the CP to metabolisable energy (CP/ME) ratio) and steer liveweight change (LWC) within and between annual cycles. High diet quality and steer liveweight (LW) gain during the RS declined progressively through the transition season (TS) and early dry season (EDS), and often the first part of the LDS. Steers commenced losing LW as the LDS progressed. In Experiments 1 and 2 where forbs comprised ≤15 g/kg of the pasture sward, steers selected strongly for forbs so that they comprised 117–236 g/kg of the diet. However, in Experiments 3 and 4 where forbs comprised substantial proportions of the pasture (173–397 g/kg), there were comparable proportions in the diet (300–396 g/kg). With appropriate stocking rates the annual steer LW gains were acceptable (121–220 kg) despite the low rainfall. The N supplements had no effect on steer LW during the TS and the EDS, but usually reduced steer LW loss by 20–30 kg during the LDS. Thus during low rainfall years in Mitchell grass pastures there were substantial LW responses by steers to N supplements towards the end of the dry season when the diet contained c. <58 g CP/kg or c. <7.0 g CP/MJ ME.

Breaking the wildfire cycle: progressive fire management can shift fire regimes and improve ecosystem condition. A case study from a large conservation reserve in northern Australia

Extensive late dry season fires in northern Australia have long been considered detrimental to biodiversity conservation, pastoral production and other cultural and landscape values. Fire management programs in these landscapes typically aim to shift the fire regime from wildfires occurring predominately in the late dry season (LDS), when they tend to be extensive and destructive, to prescribed burns in the early dry season (EDS), when fires are generally smaller and less intensive. The intent is to create heterogeneity in vegetation age classes, reduce the scale of LDS fires and, in doing so, retain long-unburnt vegetation, a critical asset for biodiversity in a flammable landscape. Boodjamulla National Park, in Queensland’s Gulf Country, experienced a cycle of large LDS wildfires every 5 years for most of its history as a pastoral property and park until a progressive EDS burning program was introduced. Although there is limited information for defining the ideal fire regime for spinifex (Triodia spp.) rangelands, this program has improved a range of spatial metrics which the Queensland Parks and Wildlife Service (QPWS) believes can only benefit biodiversity; these include decreased annual and LDS area burnt; a greater number of small burnt patches; shorter distances between recently burnt and long-unburnt spinifex; and, consequently, a greater area of long-unburnt spinifex embedded in the mosaic across the landscape. There has been an improvement in the ecological parameters of these landscapes, as well as the protection and persistence of fire-sensitive vegetation communities and species, because of the burn program.

Utilisation of Woody Plants by the Cape Porcupine in Mesic Savannas in South Africa.

Herbivory plays a fundamental role in determining the structure of savannas. The impacts of small and medium-sized mammalian herbivores on trees in savannas remain poorly understood because most research attention focuses on large herbivores such as elephants whose destructive effects on trees can be pervasive at landscape scales. On the other hand, feeding activities of generalist herbivores such as Cape porcupines on woody plants can lead to tree mortality. This study investigated the utilisation of woody plants by the Cape porcupine in three mesic savanna sites in South Africa. We determined the woody plant diet of the porcupine for the early and late dry seasons at Roodeplaat Farm in Gauteng Province, and at Goss Game Farm and Bisley Valley Nature Reserve in KwaZulu-Natal Province. Thirty and twenty randomly located quadrats (30 m × 30 m) were laid at Roodeplaat and Goss, respectively, while 10 smaller quadrats (10 m × 10 m) were laid at Bisley. We measured stem diameter and the length and width of bark scars made by porcupines on stems of woody plants. We collected ten dung samples from each study site in the wet and dry seasons for quantification of woody material in porcupine diet. Porcupine foraging behaviour impacted different tree species at each site: Vachellia robusta at Roodeplaat, Spirostachys africana at Goss and Vachellia nilotica at Bisley. Each of these trees was dominant at each site. More scarring and tree mortality were recorded at Bisley with almost 70% tree sapling mortality occurring on trees that porcupine fed on. The size of bark scars was greater at Goss (P < 0.01) than at Roodeplaat and Bisley, which were similar. The area of bark damage on S. africana trees differed significantly by stem diameter size class (P = 0.007) and was greater for small stems (size class < 7.1 cm) than the larger stems (size classes 7.1-14 cm and 14.1-21). For all the study sites, dung samples revealed that woody material contributed over 80% of the porcupine diet during the dry season, but was lower at 35% during the wet season for Roodeplaat, although it was consistently high for Bisley at 79%. Porcupine foraging activities substantially contributed to tree mortality at each site. We posit that porcupine induced mortality on dominant tree species at each site may contribute to structural heterogeneity in woody plant vegetation in mesic savannas.

Reproductive cycle in the male African fruit bat (Epomops franqueti)

Epomops franqueti is common in Sub-Saharan Africa. Unlike micro chiropteran, information on the reproductive activity of this bat is scanty. The morpho-physiology of the testis and epididymis of E. franqueti was investigated to determine the seasonal reproductive activity. Sixty adult male E. franqueti were captured at the University of Ibadan, Nigeria. Histomorphometry of the testis and epididymis was investigated. Serum hormonal assays were carried out using ELISA. Concentrations of testosterone, FSH, and LH were least (0.25, 5.80, and 7.01 IU/L, respectively) and highest (3.80, 12.03 and 14.04 IU/L, respectively) during late dry and late wet seasons, respectively, being significantly different. The early and late wet seasons had the highest gonadosomatic (0.20%) and epididymal mass (0.08%) indices, respectively. The least values were recorded during the early dry season for both gonadosomatic (0.15%) and epididymal mass (0.06%) indices. Epomops franqueti may be a seasonal breeder.

Breeding Aspects of the Toco Toucan and the Chestnut-eared Aracari (Aves, Ramphastidae) in the Brazilian Cerrado

Toucans are among the most conspicuous and famous birds in the Neotropics, but numerous aspects of their biology remain poorly known. The Toco Toucan (Ramphastos toco) and the Chestnut-eared Aracari (Pteroglossus castanotis) are commonly found in central Brazil, where studies on their breeding are scarce. The objective of this study was to examine aspects of their breeding in the Brazilian Cerrado. Searches for photographs with evidence of breeding activities were done in the WikiAves database. Citizens produced 126 records of copulations, nests, eggs and/or young. Records of the Toco Toucan (n = 92) tended to be concentrated in central and southeastern Cerrado, while those of the Chestnut-eared Aracari (n = 34) occurred mainly in its central and southwestern regions. Nests of the Toco Toucan were in hollows of palm and non-palm trees, termite nests and a pole. They were in native or human-modified habitats, and had 2–3 eggs or young in the early rainy period (OctoberDecember). On the other hand, nests of the Chestnut-eared Aracari were in hollows of non-palm trees in unknown habitats; regarding these records, a single nestling was found in the nest entrance in November, and clutch and brood sizes were unknown. Records of copulations, eggs and young in the nest indicate that the onset of breeding season of both species occurs from the late dry season to the early rainy season. Records of young indicate that the breeding seasons might reach the dry season in the Cerrado. Citizen science can improve our knowledge about toucans.

Risk of Human Exposure to the Intestinal Schistosome, Schistosoma mansoni, across Seasons along the Senegal River

Background: Schistosomiasis is an emerging disease associated with changes to the environment that have increased human contact rates with disease-causing parasites, flatworms that are released from freshwater snails. For example, schistosomiasis remains a major public health problem in Northern Senegal, where prevalence in schoolchildren often reaches 90%. Aim: This study focuses on the impact of seasonality on the risk of human exposure (RHE) to Schistosoma mansoni, defined as the total number of cercariae (the free-living life stage that infects humans) shed from all Biomphalaria pfeifferi snails collected at a site using standardized methods. We focus on RHE because it is rarely quantified and a recent study demonstrated that snails stop shedding cercariae when snail densities increase and thus per capita snail resources become limited [2], suggesting that densities of snails might not be directly proportional to RHE to schistosomes. Method: We sampled four water access points in three villages every other week during the early (Dry1) and later dry seasons (Dry2) and the rainy season, quantifying the abundance of infected and non-infected snail intermediate hosts, cercariae released per infected snail, and water chemistry. We used simple and multiple linear regressions to assess how seasonality and environmental parameters affect non-infected and infected snail abundance and RHE. Results: Although RHE was found across all seasons, the abundance of infected and non-infected snail intermediate hosts and cercariae, as well as prevalence (23.71%), were all highest in the rainy season. In the rainy season, RHE was positively associated with the density of snail hosts and their periphyton food resource. Conclusion: Although previous studies have examined the influence of seasonality on snail densities, few studies have explored the effects of seasonality on cercarial densities, which is the primary source of infection to humans. Our study demonstrates that cercarial densities are greater in the rainy season than in the early or late dry seasons. Given that cercarial densities directly pose risk of infection to humans, unlike non-infected or infected snails, these finding should help to inform decision making and schistosomiasis control efforts in West Africa.

Seasonal comparison of vavoua, biconical and NGU traps for monitoring of Glossina (Diptera: Glossinidae) and Tabanids (Diptera: Tabanidae) in The Gambia

This work shows the effective trapping method used in catching Glossinidae and Tabanidae species and their distribution in The Gambia. One hundred and eight-six traps were used in this study comprising of 62 Biconical traps, 62 NGU traps and 62 Vavoua traps for 50 trapping days. These traps were baited with at least 4 months old cow urine and acetone and they were deployed at a distance of 100 m apart. A total number of 517 flies belonging to the genus Tabanidae and Glossinidae were captured. This included: Atylotus. agrestis (55%), Tabanus sourcouf (0.4%), Tabanus par (1.2%) and T. taeniatus (1.4%), Glossina morsitan submorsitan (26%) and Glossina palpalis gambiensis (16%). However, Atylotus agrestis and Glossina palpalis gambiensis were the species that were mostly caught in this study. The present study also shows that, Lower River Region was the region with the highest number of Tabanidae species caught (85 catches, mean=20.7 and SD=16.76) while Central River Region-North also had the highest catch of Glossinidae species (52 catches, Mean= 14 and Sd=6.98). Late rainy season (October 2020) and late dry season (April 2020) were the seasons in which the highest number of Tabanidae and Glossinidae species were caught respectively. This study clearly demonstrated that, Biconical trap is the most effective trap that can be used to control the population of both Glossinidae and Tabanidae species in The Gambia.&#x0D;

Responses of a macrobenthic community to seasonal freshwater flow in a wet-dry tropical estuary

Wet-dry tropical estuaries are extreme environments driven by wet season rainfall and runoff events. The biota associated with these systems are highly adapted to large fluctuations in salinity. There are few examples globally where water extraction for human needs has not yet had a major impact on freshwater flow volumes and seasonal variability in these systems. Therefore, this study examined the importance of seasonally variable flow on intertidal macrobenthic (>0.5 mm mesh size) abundance and species composition in a pristine, wet-dry tropical estuary and nearshore environment. The focus was on intertidal mud- and sandflats where macrobenthos are known to be an important food source for endangered migratory shorebirds and fisheries species in the region. Macrobenthos on the intertidal flats were sampled on four occasions spanning the late-dry, late-flood, and early-dry periods across four years. Across all sites, total macrobenthic abundance was significantly lowest during the late-flood period, when the salinity was low, and highest in the late-dry season, under hypersaline conditions. In the muddy estuarine intertidal flats, the dominant macrobenthic group was polychaetes. In contrast, in the sandy nearshore intertidal flats, bivalves dominated in the late-dry and early-dry. However, during the late-flood, when salinities were at their lowest, the nearshore intertidal flats experienced almost complete loss of bivalves. Although flow had short-term negative effects on some species, it is clear that macrobenthos recruitment back into the intertidal flats had begun once the tide re-established in the early-dry. The differences in the flood response between polychaetes and bivalves likely reflects differences in their life history strategies, with the burrowing and swimming behaviour of polychaetes likely to be providing the ability to seek refuges during low salinity periods. Macrobenthic abundance was also correlated with benthic chlorophyll a concentrations, likely reflecting that both primary and secondary production is impacted by flow. This study suggests that macrobenthos abundance, and species dominance is driven by the seasonal changes in flow in this pristine system, demonstrating the important role of freshwater inputs.

Landscape-Scale Effects of Fire, Cats, and Feral Livestock on Threatened Savanna Mammals: Unburnt Habitat Matters More Than Pyrodiversity

Northern Australia has undergone significant declines among threatened small and medium-sized mammals in recent decades. Conceptual models postulate that predation by feral cats is the primary driver, with changed disturbance regimes from fire and feral livestock in recent decades reducing habitat cover and exacerbating declines. However, there is little guidance on what scale habitat and disturbance attributes are most important for threatened mammals, and what elements and scale of fire mosaics actually support mammals. In this study, we test a series of hypotheses regarding the influence of site-scale (50 × 50 m) habitat and disturbance attributes, as well as local-scale (1 km radius), meta-local scale (3 km), landscape-scale (5 km) and meta-landscape scale (10 km) fire mosaic attributes on mammal abundance and richness. We found that habitat cover (rock, perennial grass, and shrub cover) at the site-scale had a positive effect, and disturbance factors (feral cats, fire, feral livestock) had a negative influence on mammal abundance and richness. Models supported site-scale habitat and disturbance factors as more important for mammals than broader-scale (local up to meta-landscape scale) fire mosaic attributes. Finally, we found that increasing the extent of ≥ 4 year unburnt habitat, and having an intermediate percentage (ca. 25%) of recently burnt (1-year burnt) habitat within the mosaic, were the most important functional elements of the fire mosaic at broad scales for mammals. Contrary to expectations, diversity of post-fire ages (‘pyrodiversity’) was negatively associated with mammal abundance and richness. These results highlight the need for management to promote retention of longer unburnt vegetation in sufficient patches across savanna landscapes (particularly of shrub and fruiting trees), maintain low-intensity patchy fire regimes, reduce the extent of intense late dry season wildfires, and to reduce the impact of feral livestock. This study provides further evidence for the role of feral cats in northern Australian mammal declines, and highlights the need for increased research into the efficacy of cat control methodologies in reducing biodiversity impacts in these extensive landscapes.

Assessment of the Extent and Causes of Fuelwood Collection in the Surrounding Communities of Kasewe Reserved Forest, Sierra Leone

&#x0D; &#x0D; &#x0D; Seven (7) communities living in and around the Kasewe forest reserved were sampled to assess the extent and causes of fuelwood collection from the reserved forest involving 50 individuals in stratified random technique with a view to evaluate the degree and reasons for fuelwood collection from the Kasewe reserved forest. Data obtained indicate a high frequency of fuelwood harvest in the forest throughout the year. The significant factors affecting such decisions were availability and accessibility, ensure fast cooking process, and cost-effective. In addition, fuelwood activities were intensive throughout the year but peaks late dry season. Hence 48 (96%) of respondents stated forest degradation as one of the significant threats posed by fuelwood collectors to the forest. The study indicates that 100% of the collector are unemployed this was mainly the reason why residents of those communities collect fuelwood from the reserved forest. However, this study concluded that fuelwood collectors were selective over the kind of species they harvest, but the preferred species were not replanted. Fuelwood in the study area is not restricted to domestic use as it is also sold to augment local income. The sale of fuelwood is probably the biggest threat to sustainable utilization of fuelwood and the forest. Therefore, this study recommends that alternatives sources of livelihood and energy be created, among other recommendations for resident communities that will reduce the frequency of harvest from the forest.&#x0D; &#x0D; &#x0D;

Changes in biomass burning, wetland extent, or agriculture drive atmospheric NH&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; trends in select African regions

Abstract. Atmospheric ammonia (NH3) is a precursor to fine particulate matter and a source of nitrogen (N) deposition that can adversely affect ecosystem health. The main sources of NH3 – agriculture and biomass burning – are undergoing are or expected to undergo substantial changes in Africa. Although evidence of increasing NH3 over parts of Africa has been observed, the mechanisms behind these trends are not well understood. Here we use observations of atmospheric NH3 vertical column densities (VCDs) from the Infrared Atmospheric Sounding Interferometer (IASI) along with other satellite observations of the land surface and atmosphere to evaluate how NH3 concentrations have changed over Africa from 2008 through 2018, and what has caused those changes. In West Africa NH3 VCDs are observed to increase during the late dry season, with increases of over 6 % yr−1 in Nigeria during February and March (p&lt;0.01). These positive trends are associated with increasing burned area and CO trends during these months, likely related to agricultural preparation. Increases are also observed in the Lake Victoria basin region, where they are associated with expanding agricultural area. In contrast, NH3 VCDs declined over the Sudd wetlands in South Sudan by over 1.5 % yr−1, though not significantly (p=0.28). Annual maxima in NH3 VCDs in South Sudan occur during February through May and are associated with the drying of temporarily flooded wetland soils, which favor emissions of NH3. The change in mean NH3 VCDs over the Sudd is strongly correlated with variation in wetland extent in the Sudd: in years when more area remained flooded during the dry season, NH3 VCDs were lower (r=0.64, p&lt;0.05). Relationships between biomass burning and NH3 may be observed when evaluating national-scale statistics: countries with the highest rates of increasing NH3 VCDs also had high rates of growth in CO VCDs; burned area displayed a similar pattern, though not significantly. Livestock numbers were also higher in countries with intermediate or high rates of NH3 VCD growth. Fertilizer use in Africa is currently low but growing; implementing practices that can limit NH3 losses from fertilizer as agriculture is intensified may help mitigate impacts on health and ecosystems.

Environmental Implication of Thermal Radiation on the Physiochemical Properties of Soil around Gas Flare Sites in the Niger Delta Region of Nigeria

The effect of thermal radiation on the Physiochemical properties of soil around gas flare site in the Niger Delta region was assessed in Emuoha Local Government Area of River State, Nigeria, for a period of twelve months. Radiation profile was determined at different times (hours) – 6, 10, 14, 18 and 22, in the four seasons (early dry, early wet, late dry and late wet) of the year. Soil samples were taken at different depths (cm) (0-15 and 15-30) for physicochemical attributes at different distances (m) (0-150, 150-300, 300-450, 450-600 and 1000 -2000) from the flare site and thermal radiation was also determined at the respective distances. Results of effect of time and seasonal variations on radiation profile showed that environmental temperature (oC) ranged from 29.2 ± 0.3 at 22 hours of early wet season to 33.0 ± 0.4 at 14 hours of late dry season; radiation temperature ranged from 35.4 ± 1.2 at 22 hours of late wet season to 42.0 ± 1.4 at 14 hours of late dry season, while thermal radiation (w/m2) ranged from 490.83 ± 7.7 at 22 hours of late wet season to 535.69 ± 9.69 at 14 hours of late dry season. Results of effect of flare distance on physicochemical properties of soil showed that as the distance (m) from flare site increases from 0 – 150 to 1000 – 2000, the radiation intensity (w/m2) decreases from 603.84 ± 5.7 – 428.83 ± 0.75, and values of pH, OC, N, P, and exchangeable cations - K+, Na+, Ca2+, Mg2+ increases in the range {pH (4.94 ± 0.02 – 5.50 ± 0.00), OC (1.09 ± 0.01 – 2.05 ± 0.00), N (0.07 ±0.01 – 0.09 ± 0.00), P (10.90 ± 0.03 – 12.10 ± 5.19), K+ (0.28 ± 0.01 – 1.86 ± 0.01), Na+ (0.48 ± 0.00 – 1.04 ± 0.00), Ca2+ (1.65 ± 0.01 – 2.85 ± 0.00), Mg2+ (0.73 ± 0.01 – 1.24 ± 0.01)}, These values seemed not to be affected by the thermal radiation and flare distance , oil and grease and THC decreases in the range 203.30 ± 0.88 – 61.33 ± 0.33 and 352.90 ± 2.08 – 10.04 ± 0.04 respectively. Similar trend was observed with soil samples taken at 15-30cm depth. Statistical analysis showed there is significant difference (p&lt;0.001) in soil attributes as distance from flare distance increases. Further studies should be carried out to investigate the relationship between soil around flare site and crop performance on different agro-ecological zone of Rivers State.

Influence of trees on landscape temperature in semi-arid agro-ecosystems of East Africa

In the Dodoma region of Tanzania, overexploitation of natural resources has led to a severe land degradation and, consequently, to the need to restore local ecosystems. Within the possible strategies, the farmer managed natural regeneration agroforestry is strongly being promoted in the area. To validate the utilisation of this practise, this research aims (i) to assess the benefits of trees on microclimate studying the relationship between land surface temperature (LST) and tree canopy cover (TCC) in farmlands and (ii) to propose an operative tree density threshold to be set as objective by restoration activities in the area. Data collected with an unmanned aerial vehicle were integrated with Landsat 8 and Sentinel 2 satellite imagery. LST was retrieved through the practical single channel algorithm and TCC was calculated with a supervised classification. Pixel-based analyses at a resolution of 30 m and 10 m were performed, and the resulting data statistically analysed through the coefficient of determination, the Kruskal–Wallis test, and the Dunn test. Results showed that the TCC of the surveyed areas was 5.1%, and a significant decrease in LST of 1.32 °C (p < 0.01) was found in the areas with the highest TCC, during the late dry season. From these preliminary analyses, a threshold of 10% TCC is suggested for farmlands in this agroecological zone to bring beneficial microclimate changes in terms of temperature. Considering the average plant phenotype characteristic of the area, it corresponds to a tree density of 50 trees ha −1 . • LST decrease of 1.32 °C found in areas with high TCC in the late dry season. • 10% TCC threshold, or 50 trees ha −1 should be reached using restoration. • Integration of Landsat 8 with Sentinel 2 data gave improved analysis.

Vocal communication in wild chimpanzees: a call rate study.

BackgroundPatterns of vocal communication have implications for species conservation: a change in calling behaviour can, for instance, reflect a disturbed habitat. More importantly, call rate is a parameter that allows conservation planners to convert call density into animal density, when detecting calls with a passive acoustic monitoring system (PAM).MethodsWe investigated chimpanzee (Pan troglodytes schweinfurthii) call rate during the late dry season in the Issa Valley, western Tanzania by conducting focal follows. We examined the socio-ecological factors that influence call production rate of savanna woodland chimpanzees.ResultsWe found that sex, proportion of time spent in a vegetation type, proportion of time spent travelling, time of the day, party size and swollen parous female presence had a significant effect on the call rate. Call rate differed among the different demographic classes with subadult and adult males vocalising twice as often as the subadult and adult females and three times as often as the juveniles.ApplicationsThe use of PAM and recent statistical developments to estimate animal density is promising but relies on our knowing individual call rate, often not available for many species. With the improvement in automatic call detection, we anticipate that PAM will increasingly be broadly applied to primates but also across taxa, for conservation.

Will fencing floodplain and riverine wetlands from feral pig damage conserve fish community values?

Installation of feral pig (Sus scrofa) exclusion fences to conserve and rehabilitate coastal floodplain habitat for fish production and water quality services remains untested. Twenty‐one floodplain and riverine wetlands in the Archer River catchment (north Queensland) were surveyed during postwet (June–August) and late‐dry season (November–December) in 2016, 2017, and 2018, using a fyke net soaked overnight (~14–15 hr) to test: (a) whether the fish assemblage are similar in wetlands with and without fences; and (b) whether specific environmental conditions influence fish composition between fenced and unfenced wetlands. A total of 6,353 fish representing twenty‐six species from 15 families were captured. There were no wetland differences in fish assemblages across seasons, years and for fenced and unfenced (PERMANOVA, Pseudo‐F < 0.589, p < .84). Interestingly, the late‐dry season fish were far smaller compared to postwet season fish: a strategy presumably in place to maximize rapid disposal following rain and floodplain connectivity. In each wetland, a calibrated Hydrolab was deployed (between 2 and4 days, with 20 min logging) in the epilimnion (0.2 m) and revealed distinct diel water quality cycling of temperature, dissolved oxygen and pH (conductivity represented freshwater wetlands), which was more obvious in the late‐dry season survey because of extreme summer conditions. Water quality varied among wetlands in terms of the daily amplitude and extent of daily photosynthesis recovery, which highlights the need to consider local conditions and that applying general assumptions around water quality conditions for these types of wetlands is problematic for managers. Though many fish access wetlands during wet season connection, the seasonal effect of reduced water level conditions seems more overimprovised when compared to whether fences are installed, as all wetlands supported few, juvenile, or no fish species because they had dried completely regardless of the presence of fences.

Seasonality of adverse birth outcomes in women with and without HIV in a representative birth outcomes surveillance study in Botswana

IntroductionSub-Saharan Africa has the largest number of people with HIV, one of the most severe burdens of adverse birth outcomes globally and particular vulnerability to climate change. We examined associations...

Functional heterogeneity of habitats and dry season forage variability in an Okavango Delta landscape, northern Botswana

The late dry season is a period when forage resources become limited in some African savannas that can induce a strong demographic bottleneck in herbivore populations with limited access to resource heterogeneity. This study determined forage quality and quantity between wetlands and drylands habitats during the late dry season. We subjectively sampled forage characteristics in four habitat types around the distal reaches of the Tsum Tsum floodplains of the Okavango Delta during the late dry season of 2015. The habitat types were mopane and sandveld woodland far from floodplains (two major dryland habitat types), sandveld habitats that receive soil moisture inputs from adjacent floodplains (wet sandveld) and sedgeland habitat within the floodplain. Leaves collected from forage in each habitat type were oven dried, milled and analysed for total nitrogen. Data of greenness, height, biomass and protein were analysed using Kruskal-Wallis test. Forage in wet sandveld had by far the highest protein content (~16%) of all habitat types but forage height and biomass were very low, whereas sedgelands had the highest biomass of adequate-quality forage, while dryland communities had the lowest quantity and quality of forage. Thus, foraging between a higher-biomass, adequate-quality reserve resource (sedgeland) and a high-quality but low-quantity bridging resource (wet sandveld) can help to ensure a balanced protein and fibre intake during the late dry season. Our study demonstrated the importance of wetland habitats for providing green forage with sufficient biomass and protein to sustain herbivores over the late dry season.

The combined effect of discharge and tides on low-angle dune evolution at the tidal current limit of the Changjiang Estuary

Low-angle dunes (LADs) are recognized as the most common roughness element in large fluvial rivers and estuaries. Comprehending their development is vital to understand the flow and sediment dynamics, and paleo-environmental reconstruction of the geological record. However, our understanding of LADs evolution under unsteady flows is poorly understood. Here we investigate dune adaptation under the combined effect of discharge and tides at the tidal current limit of the Changjiang Estuary. Our observations show that compound dunes exist in the late flood season, while only simple dunes are found in the late dry season after five-month decay. The effect of tides enhances bedload transport, thereby accelerating the decay of compound dunes. The increasing deformation rate of superimposed small dunes from the trough to the crest of primary dunes results in a decrease in dune size in the neap tide, as superimposed dunes over the higher part of primary dunes decay more significantly. We find that the size of superimposed small dunes in the late flood season and simple dunes in the late dry season are significantly controlled by fortnightly tides when discharge is between 20,000 and 30,000 m3/s. It implies that compound dunes decay with crest erosion via frequent migration and deformation of superimposed small dunes between neap and spring tides. This finding could potentially help identify and interpret paleo-hydraulic environments that were influenced by tides from sedimentary records. Additionally, given the discharge of the lower Changjiang River is increasingly regulated by dams, figuring out dune adaptation to the regulated hydrograph could be used to advance our prediction of the evolution of river morphology.