Etosha National Park Research Articles

Authenticity, Identity, and Humanity: The Hai‖om San and the State of Namibia

The Hai‖om are the largest and most widely dispersed San population in Namibia. Like many other San peoples in Southern Africa, the Hai‖om were dispossessed, marginalised, and discriminated against by other groups and by the colonial state. In 1949, the South West African administration appointed a Commission for the Preservation of the Bushmen, chaired by a former Stellenbosch University professor, P.J. Schoeman, one of the architects of apartheid in South Africa. When the final report of the Commission was published in 1953, the Hai‖om were ignored, in part because Schoeman did not see them as ‘real' or ‘authentic' Bushmen. The Hai‖om were removed from their ancestral homeland in what was designated as Etosha National Park in 1953–1954. This paper examines the efforts of the Hai‖om to seek land and resource rights and political recognition from the 1980s to the present. The Namibian government appointed a Hai‖om Traditional Authority, David//Khamuxab, in 2004, established a San Development Office in the Office of the Deputy Prime Minister in 2005, and in 2007 began purchasing commercial farms for purposes of resettlement of Hai‖om. Statements by Namibian government officials underscore the importance of humanity and compassion in the ways in which the Hai‖om San issue has been addressed. It remains to be seen, however, whether the Hai‖om of Etosha will be treated the same way as other Hai‖om and other historically disadvantaged or marginalised communities in Namibia.

Seasonal patterns of hormones, macroparasites, and microparasites in wild African ungulates: the interplay among stress, reproduction, and disease.

Sex hormones, reproductive status, and pathogen load all affect stress. Together with stress, these factors can modulate the immune system and affect disease incidence. Thus, it is important to concurrently measure these factors, along with their seasonal fluctuations, to better understand their complex interactions. Using steroid hormone metabolites from fecal samples, we examined seasonal correlations among zebra and springbok stress, reproduction, gastrointestinal (GI) parasite infections, and anthrax infection signatures in zebra and springbok in Etosha National Park (ENP), Namibia, and found strong seasonal effects. Infection intensities of all three GI macroparasites examined (strongyle helminths, Strongyloides helminths, and Eimeria coccidia) were highest in the wet season, concurrent with the timing of anthrax outbreaks. Parasites also declined with increased acquired immune responses. We found hormonal evidence that both mares and ewes are overwhelmingly seasonal breeders in ENP, and that reproductive hormones are correlated with immunosuppression and higher susceptibility to GI parasite infections. Stress hormones largely peak in the dry season, particularly in zebra, when parasite infection intensities are lowest, and are most strongly correlated with host mid-gestation rather than with parasite infection intensity. Given the evidence that GI parasites can cause host pathology, immunomodulation, and immunosuppression, their persistence in ENP hosts without inducing chronic stress responses supports the hypothesis that hosts are tolerant of their parasites. Such tolerance would help to explain the ubiquity of these organisms in ENP herbivores, even in the face of their potential immunomodulatory trade-offs with anti-anthrax immunity.

Horns and Thorns (Two springboks foraging) Two springboks, Antidorcas marsupialis, savouring the highly-nutritive flowers of the leafless Water Thorn, Acacia nebrownii, shrubs in Etosha National Park, Nambia. Photograph reproduced by permission of Emmanue

Horns and Thorns (Two springboks foraging) Two springboks, Antidorcas marsupialis, savouring the highly-nutritive flowers of the leafless Water Thorn, Acacia nebrownii, shrubs in Etosha National Park, Nambia. Photograph reproduced by permission of Emmanue

A sylvatic lifecycle of Echinococcus equinus in the Etosha National Park, Namibia.

Various species of Echinococcus have been described in the past from wild mammals of sub-Saharan Africa. However, it is only recently, that a few isolates have become available for molecular identification; therefore, the involvement of wildlife in the lifecycles of the various cryptic species within Echinococcus granulosus sensu lato is still only partially known. A preliminary survey was undertaken in Etosha National Park, Namibia, from August to October 2012. Faecal samples were obtained from 34 individual wild carnivores, and metacestodes were collected from carcasses of 18 culled herbivores. Single eggs and metacestode tissue were lysed and identified from sequences of the mitochondrial nad1 gene. In case of metacestodes, the cox1 gene was additionally sequenced and haplotype networks were constructed. Echinococcus equinus was found in lions (4 of 6), black-backed jackals (2 of 7) and Burchell's zebras (11 of 12). The frequency of this parasite in the absence of domestic dogs, horses and donkeys strongly indicates its transmission in a wildlife cycle. Further, a variety of sequences were obtained from eggs and cysticerci from lions, cheetahs, caracals, spotted hyenas and oryx, which most closely clustered with species of Taenia. Only 3 of them, 2 of lion and 1 of hyena origin, could be allocated to Hydatigera (=Taenia) taeniaeformis (lion), Taenia regis (lions and oryx) and Taenia cf. crocutae (spotted hyena and oryx).

A pride of African Lions, Panthera leo , feeding on a Plains Zebra, Equus quagga , in Etosha National Park, Namibia. Photograph reproduced by permission of Emmanuel Do Linh San - www.pbase.com/emmanueldolinhsan

EthologyVolume 121, Issue 1 p. i-i Front CoverFree Access A pride of African Lions, Panthera leo, feeding on a Plains Zebra, Equus quagga, in Etosha National Park, Namibia. Photograph reproduced by permission of Emmanuel Do Linh San - www.pbase.com/emmanueldolinhsan First published: 01 December 2014 https://doi.org/10.1111/eth.12300AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume121, Issue1January 2015Pages i-i RelatedInformation

Fatal attraction: vegetation responses to nutrient inputs attract herbivores to infectious anthrax carcass sites.

Parasites can shape the foraging behaviour of their hosts through cues indicating risk of infection. When cues for risk co-occur with desired traits such as forage quality, individuals face a trade-off between nutrient acquisition and parasite exposure. We evaluated how this trade-off may influence disease transmission in a 3-year experimental study of anthrax in a guild of mammalian herbivores in Etosha National Park, Namibia. At plains zebra (Equus quagga) carcass sites we assessed (i) carcass nutrient effects on soils and grasses, (ii) concentrations of Bacillus anthracis (BA) on grasses and in soils, and (iii) herbivore grazing behaviour, compared with control sites, using motion-sensing camera traps. We found that carcass-mediated nutrient pulses improved soil and vegetation, and that BA is found on grasses up to 2 years after death. Host foraging responses to carcass sites shifted from avoidance to attraction, and ultimately to no preference, with the strength and duration of these behavioural responses varying among herbivore species. Our results demonstrate that animal carcasses alter the environment and attract grazing hosts to parasite aggregations. This attraction may enhance transmission rates, suggesting that hosts are limited in their ability to trade off nutrient intake with parasite avoidance when relying on indirect cues.

Gastrointestinal helminths may affect host susceptibility to anthrax through seasonal immune trade-offs.

BackgroundMost vertebrates experience coinfections, and many pathogen-pathogen interactions occur indirectly through the host immune system. These interactions are particularly strong in mixed micro-macroparasite infections because of immunomodulatory effects of helminth parasites. While these trade-offs have been examined extensively in laboratory animals, few studies have examined them in natural systems. Additionally, many wildlife pathogens fluctuate seasonally, at least partly due to seasonal host immune changes. We therefore examined seasonality of immune resource allocation, pathogen abundance and exposure, and interactions between infections and immunity in plains zebra (Equus quagga) in Etosha National Park (ENP), Namibia, a system with strongly seasonal patterns of gastrointestinal (GI) helminth infection intensity and concurrent anthrax outbreaks. Both pathogens are environmentally transmitted, and helminth seasonality is driven by environmental pressures on free living life stages. The reasons behind anthrax seasonality are currently not understood, though anthrax is less likely directly driven by environmental factors.ResultsWe measured a complex, interacting set of variables and found evidence that GI helminth infection intensities, eosinophil counts, IgE and IgGb antibody titers, and possibly IL-4 cytokine signaling were increased in wetter seasons, and that ectoparasite infestations and possibly IFN-γ cytokine signaling were increased in drier seasons. Monocyte counts and anti-anthrax antibody titers were negatively associated with wet season eosinophilia, and monocytes were negatively correlated with IgGb and IgE titers. Taken together, this supports the hypothesis that ENP wet seasons are characterized by immune resource allocation toward Th-2 type responses, while Th1-type immunity may prevail in drier seasons, and that hosts may experience Th1-Th2 trade-offs. We found evidence that this Th2-type resource allocation is likely driven by GI parasite infections, and that these trade-offs may render hosts less capable of concurrently mounting effective Th1-type immune responses against anthrax.ConclusionsThis study is one of the first to examine laboratory-demonstrated Th1-Th2 trade-offs in a natural system. It provides evidence that seasonally bound pathogens may affect, through immunology, transmission dynamics of pathogens that might otherwise not be seasonally distributed. It suggests that, by manipulating the internal host ecosystem, GI parasites may influence the external ecosystem by affecting the dynamics of another environmentally transmitted pathogen.Electronic supplementary materialThe online version of this article (doi:10.1186/s12898-014-0027-3) contains supplementary material, which is available to authorized users.

Endolysin from Giant Bacteriophage Disrupts B. anthracis

The endolysin enzyme from a giant but mostly temperate bacteriophage, recovered from a zebra carcass as well as a nearby soil sample in Etosha National Park in Namibia, Africa, is effective in disrupting Bacillus anthracis and other Bacillus species, according to Holly Ganz at the University of California, Davis, Jochen Klumpp of ETH Zurich in Zurich, Switzerland, and their collaborators. Subsequent analysis helps to explain the broad host range of this unusual phage and provides details about how it interacts with its bacterial hosts. Details appeared 27 January 2014 in PLoS ONE (doi:10.1371/journal.pone.0085972).

Seasonal variation in foraging behaviour of plains zebra (Equus quagga) may alter contact with the anthrax bacterium (Bacillus anthracis)

Pathogens transmitted via the environment are often aggregated in space, and seasonal variation in wildlife foraging behaviour may alter contact rates with environmental pathogens. The soil-borne bacterium Bacillus anthracis Cohn, 1872 causes anthrax, and herbivores acquire gastrointestinal anthrax by ingesting spores. Therefore host foraging behaviour could be a fundamental component of anthrax epidemiology. This study investigated seasonal changes in bite density and diet of plains zebras (Equus quagga Boddaert, 1785) in relation to anthrax seasonality in Etosha National Park, Namibia, where most zebra anthrax cases are observed in wet seasons. The diet of zebras shifted from more short grasses during the wet season to more tall grasses in the dry season, suggesting a greater potential for soil ingestion in wet seasons. Zebras also foraged most intensively in the wet season with the number of bites/step declining through the dry season. This higher bite density in wet seasons may lead individuals to ingest greater concentrations of the pathogen if foraging in a localized infectious area. Although sex and reproductive state affected bite density, no sex difference in anthrax occurrence was observed. This study demonstrates how considering variation in host foraging behaviour may enhance our understanding of disease seasonality for pathogens with foraging-dependent transmission.

Frequent and seasonally variable sublethal anthrax infections are accompanied by short‐lived immunity in an endemic system

Few studies have examined host-pathogen interactions in wildlife from an immunological perspective, particularly in the context of seasonal and longitudinal dynamics. In addition, though most ecological immunology studies employ serological antibody assays, endpoint titre determination is usually based on subjective criteria and needs to be made more objective. Despite the fact that anthrax is an ancient and emerging zoonotic infectious disease found world-wide, its natural ecology is not well understood. In particular, little is known about the adaptive immune responses of wild herbivore hosts against Bacillus anthracis. Working in the natural anthrax system of Etosha National Park, Namibia, we collected 154 serum samples from plains zebra (Equus quagga), 21 from springbok (Antidorcas marsupialis) and 45 from African elephants (Loxodonta africana) over 2-3years, resampling individuals when possible for seasonal and longitudinal comparisons. We used enzyme-linked immunosorbent assays to measure anti-anthrax antibody titres and developed three increasingly conservative models to determine endpoint titres with more rigourous, objective mensuration. Between 52 and 87% of zebra, 0-15% of springbok and 3-52% of elephants had measurable anti-anthrax antibody titres, depending on the model used. While the ability of elephants and springbok to mount anti-anthrax adaptive immune responses is still equivocal, our results indicate that zebra in ENP often survive sublethal anthrax infections, encounter most B. anthracis in the wet season and can partially booster their immunity to B.anthracis. Thus, rather than being solely a lethal disease, anthrax often occurs as a sublethal infection in some susceptible hosts. Though we found that adaptive immunity to anthrax wanes rapidly, subsequent and frequent sublethal B.anthracis infections cause maturation of anti-anthrax immunity. By triggering host immune responses, these common sublethal infections may act as immunomodulators and affect population dynamics through indirect immunological and co-infection effects. In addition, with our three endpoint titre models, we introduce more mensuration rigour into serological antibody assays, even under the often-restrictive conditions that come with adapting laboratory immunology methods to wild systems. With these methods, we identified significantly more zebras responding immunologically to anthrax than have previous studies using less comprehensive titre analyses.

Novel Giant Siphovirus from Bacillus anthracis Features Unusual Genome Characteristics

Here we present vB_BanS-Tsamsa, a novel temperate phage isolated from Bacillus anthracis, the agent responsible for anthrax infections in wildlife, livestock and humans. Tsamsa phage is a giant siphovirus (order Caudovirales), featuring a long, flexible and non-contractile tail of 440 nm (not including baseplate structure) and an isometric head of 82 nm in diameter. We induced Tsamsa phage in samples from two different carcass sites in Etosha National Park, Namibia. The Tsamsa phage genome is the largest sequenced Bacillus siphovirus, containing 168,876 bp and 272 ORFs. The genome features an integrase/recombinase enzyme, indicative of a temperate lifestyle. Among bacterial strains tested, the phage infected only certain members of the Bacillus cereus sensu lato group (B. anthracis, B. cereus and B. thuringiensis) and exhibited moderate specificity for B. anthracis. Tsamsa lysed seven out of 25 B. cereus strains, two out of five B. thuringiensis strains and six out of seven B. anthracis strains tested. It did not lyse B. anthracis PAK-1, an atypical strain that is also resistant to both gamma phage and cherry phage. The Tsamsa endolysin features a broader lytic spectrum than the phage host range, indicating possible use of the enzyme in Bacillus biocontrol.

Gastrointestinal helminths may affect host susceptibility to anthrax through seasonal immune trade-offs

BackgroundMost vertebrates experience coinfections, and many pathogen-pathogen interactions occur indirectly through the host immune system. These interactions are particularly strong in mixed micro-macroparasite infections because of immunomodulatory effects of helminth parasites. While these trade-offs have been examined extensively in laboratory animals, few studies have examined them in natural systems. Additionally, many wildlife pathogens fluctuate seasonally, at least partly due to seasonal host immune changes. We therefore examined seasonality of immune resource allocation, pathogen abundance and exposure, and interactions between infections and immunity in plains zebra (Equus quagga) in Etosha National Park (ENP), Namibia, a system with strongly seasonal patterns of gastrointestinal (GI) helminth infection intensity and concurrent anthrax outbreaks. Both pathogens are environmentally transmitted, and helminth seasonality is driven by environmental pressures on free living life stages. The reasons behind anthrax seasonality are currently not understood, though anthrax is less likely directly driven by environmental factors.ResultsWe measured a complex, interacting set of variables and found evidence that GI helminth infection intensities, eosinophil counts, IgE and IgGb antibody titers, and possibly IL-4 cytokine signaling were increased in wetter seasons, and that ectoparasite infestations and possibly IFN-γ cytokine signaling were increased in drier seasons. Monocyte counts and anti-anthrax antibody titers were negatively associated with wet season eosinophilia, and monocytes were negatively correlated with IgGb and IgE titers. Taken together, this supports the hypothesis that ENP wet seasons are characterized by immune resource allocation toward Th-2 type responses, while Th1-type immunity may prevail in drier seasons, and that hosts may experience Th1-Th2 trade-offs. We found evidence that this Th2-type resource allocation is likely driven by GI parasite infections, and that these trade-offs may render hosts less capable of concurrently mounting effective Th1-type immune responses against anthrax.ConclusionsThis study is one of the first to examine laboratory-demonstrated Th1-Th2 trade-offs in a natural system. It provides evidence that seasonally bound pathogens may affect, through immunology, transmission dynamics of pathogens that might otherwise not be seasonally distributed. It suggests that, by manipulating the internal host ecosystem, GI parasites may influence the external ecosystem by affecting the dynamics of another environmentally transmitted pathogen.

Social networks, long-term associations and age-related sociability of wild giraffes

Long-term studies of sociality in wild animals are rare, despite being critical for determining the benefits of social relationships and testing how long such relationships last and whether they change as individuals age. Knowledge about social relationships in animal species that exhibit fission–fusion dynamics can enhance our understanding of the evolution of close social bonds in humans, who also have a fission–fusion social system. We analysed the social network of wild giraffes, Giraffa camelopardalis , in Etosha National Park, Namibia, from 1102 records of group compositions, including 625 individually identified individuals, spanning 6 years. We found that giraffes, which exhibit fission–fusion sociality, formed a cohesive society with short path lengths across the network that may facilitate passive information sharing about resource availability. Male and female giraffes appeared to contribute equally to the network structure, based on similarities between the sexes for five network metrics. However, using lagged association rates, we found that long-term relationships spanning 6 years were evident among female giraffes, but not males, which may be explained by sex differences in ranging patterns and reproductive priorities. Five network metrics of females were compared between two adult age cohorts to investigate whether females' ages influenced sociability. As younger females reached adulthood, they associated with greater numbers of females and increased their network strength and social connectivity, perhaps because of dispersal. Our study reinforces the value of network analysis and long-term studies for examining the social systems of wild animals.

Co-infection of an animal with more than one genotype can occur in anthrax

During the routine fingerprinting of outbreak strains of Bacillus anthracis of European and African origin by means of a 31-marker multi-locus variable number of tandem repeats analysis (MLVA), four cultures, two from the Etosha National Park (ENP), Namibia, and two from an outbreak in the Pyrenees in 1997, were found to harbour different genotypes (GTs). To investigate this further, isolates from 10 samples of blood-soaked soil from beneath anthrax carcasses and 18 clinical swabs taken from carcasses in the ENP were examined by a 31-marker MLVA. While only a single GT was found in any one of the 10 soil samples, four of the 18 swabs (22%) yielded different GTs. Two GTs were isolated from each of a zebra and a springbok and three GTs from each of a second zebra and an elephant. These animals had died in a region of the ENP where deaths caused by anthrax regularly occur every year. The results confirm the indications noted previously that co-infection with more than one GT is probably not especially uncommon. The results show that, for the purpose of analysing genotypes involved in an outbreak, it is important to examine more than a single colony from a clinical sample. Multi-locus variable number of tandem repeats analysis (MLVA)-based fingerprinting techniques have been used in many studies worldwide to characterize the occurrence of different genotypes of Bacillus anthracis in outbreaks of wildlife or livestock and to draw conclusions about the source, the possible routes of spread and the temporal and spatial distribution of outbreak strains. Simultaneous isolation of different genotypes from the same host revealed in our study by MLVA highlights the importance of examining more than a single colony from a clinical sample. This conclusion is not specific for MLVA but holds true for every high-resolution method, including full-genome sequencing.

A molecular analysis of African lion (Panthera leo) mating structure and extra‐group paternity in Etosha National Park

The recent incorporation of molecular methods into analyses of social and mating systems has provided evidence that mating patterns often differ from those predicted by group social organization. Based on field studies and paternity analyses at a limited number of sites, African lions are predicted to exhibit a strict within-pride mating system. Extra-group paternity has not been previously reported in African lions; however, observations of extra-group associations among lions inhabiting Etosha National Park in Namibia suggest deviation from the predicted within-pride mating pattern. We analysed variation in 14 microsatellite loci in a population of 164 African lions in Etosha National Park. Genetic analysis was coupled with demographic and observational data to examine pride structure, relatedness and extra-group paternity (EGP). EGP was found to occur in 57% of prides where paternity was analysed (n = 7), and the overall rate of EGP in this population was 41% (n = 34). Group sex ratio had a significant effect on the occurrence of EGP (P < 0.05), indicating that variation in pride-level social structure may explain intergroup variation in EGP. Prides with a lower male-to-female ratio were significantly more likely to experience EGP in this population. The results of this study challenge the current models of African lion mating systems and provide evidence that social structure may not reflect breeding structure in some social mammals.

Climate variability, human wildlife conflict and population dynamics of lions Panthera leo

Large carnivores are threatened by habitat loss, declining prey populations and direct persecution. Pride dynamics of eight lion prides in the centre of the Etosha National Park, Namibia are described during a 16-year study. Since the beginning of the 1980s, the number of adult and subadult lions declined continuously to two third of its initial population size, and reached a new equilibrium in the 1990s. Pride sizes decreased from 6.3 adult females in 1989 to 2.8 lionesses in 1997. While the number of adult females declined continuously, the number of adult males, subadult females and subadult males remained constant over the years. A severe drought period, lasting for more than 20 years, led to declining prey populations inside the lions' territory. Besides declining prey populations, conflict with humans at the border of Etosha puts substantial pressure onto the lion population: 82% of all known lion mortalities were caused by humans, and most of these consisted of adult females (28%) and subadult males (29%). I postulate that the considerable decline in the lion population is a response to declining prey populations, and although the human predator conflict is severe, it does not seem to limit the size of Etosha's lion population.

Factors Influencing Foraging Search Efficiency: Why Do Scarce Lappet-Faced Vultures Outperform Ubiquitous White-Backed Vultures?

The search phase is a critical component of foraging behavior, affecting interspecific competition and community dynamics. Nevertheless, factors determining interspecific variation in search efficiency are still poorly understood. We studied differences in search efficiency between the lappet-faced vulture (Torgos tracheliotus; LFV) and the white-backed vulture (Gyps africanus; WBV) foraging on spatiotemporally unpredictable carcasses in Etosha National Park, Namibia. We used experimental food supply and high-resolution GPS tracking of free-ranging vultures to quantify search efficiency and elucidate the factors underlying the observed interspecific differences using a biased correlated random walk simulation model bootstrapped with the GPS tracking data. We found that LFV's search efficiency was higher than WBV's in both first-to-find, first-to-land, and per-individual-finding rate measures. Modifying species-specific traits in the simulation model allows us to assess the relative role of each factor in LFV's higher efficiency. Interspecific differences in morphology (through the effect on perceptual range and motion ability) and searchers' spatial dispersion (due to different roost arrangements) are in correspondence with the empirically observed advantage of LFV over WBV searchers, whereas differences in other aspects of the movement patterns appear to play a minor role. Our results provide mechanistic explanations for interspecific variation in search efficiency for species using similar resources and foraging modes.

A hierarchical distance sampling approach to estimating mortality rates from opportunistic carcass surveillance data

Distance sampling is widely used to estimate the abundance or density of wildlife populations. Methods to estimate wildlife mortality rates have developed largely independently from distance sampling, despite the conceptual similarities between estimation of cumulative mortality and the population density of living animals. Conventional distance sampling analyses rely on the assumption that animals are distributed uniformly with respect to transects and thus require randomized placement of transects during survey design. Because mortality events are rare, however, it is often not possible to obtain precise estimates in this way without infeasible levels of effort. A great deal of wildlife data, including mortality data, is available via road-based surveys. Interpreting these data in a distance sampling framework requires accounting for the non-uniformity sampling. Additionally, analyses of opportunistic mortality data must account for the decline in carcass detectability through time. We develop several extensions to distance sampling theory to address these problems.We build mortality estimators in a hierarchical framework that integrates animal movement data, surveillance effort data, and motion-sensor camera trap data, respectively, to relax the uniformity assumption, account for spatiotemporal variation in surveillance effort, and explicitly model carcass detection and disappearance as competing ongoing processes.Analysis of simulated data showed that our estimators were unbiased and that their confidence intervals had good coverage.We also illustrate our approach on opportunistic carcass surveillance data acquired in 2010 during an anthrax outbreak in the plains zebra of Etosha National Park, Namibia.The methods developed here will allow researchers and managers to infer mortality rates from opportunistic surveillance data.

Soil ingestion, nutrition and the seasonality of anthrax in herbivores of Etosha National Park

Anthrax, caused by the bacterium Bacillus anthracis, is a seasonally occurring infectious disease affecting primarily herbivorous wildlife and livestock. The seasonality of anthrax outbreaks varies among locations, making it difficult to develop a single consistent ecological description of this disease. Over 44 years of mortality surveillance, most anthrax cases in Etosha National Park, Namibia are observed in the wet season, although elephants have an anthrax mortality peak in the dry season. Focusing on three host species (plains zebra, Equus quagga; African elephant, Loxodonta africana; and springbok, Antidorcas marsupialis) occupying the endemic anthrax area of Etosha National Park, Namibia, we tested two commonly posited causes of anthrax seasonality in herbivores: increased pathogen exposure due to greater soil contact, and increased host susceptibility due to seasonal nutritional stress. These hypotheses were assessed using fecal sampling and measurement of the percentage of fecal silicates as an index of soil ingestion and fecal nitrogen, phosphorus and crude fiber as nutritional indices. Nutritional quality for all three species was higher in wet than dry seasons. Comparing among wet seasons, nutritional indices showed either a decline in nutrition with increasing rainfall or no significant pattern. All three species had greater soil ingestion in the wet season than the dry season. Higher soil contact during the anthrax peak suggests that anthrax seasonality may in part be due to heightened exposure to B. anthracis in wet seasons, for zebra and springbok. Elephant anthrax deaths do not correspond with the season of increased soil ingestion or grazing, suggesting that other behavioral mechanisms may overshadow foraging‐based risk factors for this species. Nutritional stress is unlikely the primary causative factor in wet season anthrax systems, although nutritional stress sufficient to reduce resistance is difficult to assess non‐invasively in wild herbivores. In contrast, increased soil ingestion may be an important predisposing factor for wet season anthrax outbreaks. Ultimately, the amount of soil ingested and its importance in the transmission of soil‐borne pathogens will vary based on foraging behaviors, intake rates, grassland structure and on the likelihood that foraging areas intersect with pathogen aggregations in the environment.

Fission–fusion dynamics in wild giraffes may be driven by kinship, spatial overlap and individual social preferences

Many species exhibit fission–fusion dynamics, yet the factors that influence the frequent changes in group size and membership in these species have not been widely studied. Social ties may be influenced by kinship but animals may also form preferred associations because of social attraction or may only associate because they have similar habitat preferences. We investigated the association patterns of 535 wild giraffes, Giraffa camelopardalis, in Etosha National Park, Namibia using behavioural and genetic data from individually identified giraffes. We collected 726 records of group composition over a 14-month period and calculated pairwise association indices, which were tested against a null model. We found that female–female pairs, but not male–male pairs, showed both preferred and avoided relationships. We tested whether females' relationships could be explained by the degree of relatedness between pairs and whether pairs overlapped spatially. Correlations between matrices of pairwise associations, spatial overlap and relatedness showed that female–female associations were strongly correlated with amounts of spatial overlap and pairs that exhibited preferred relationships were more closely related than would be expected by chance. However, only about one-quarter of the variation in observed associations could be explained by spatial overlap and relatedness and therefore much of this variation may have been related to individual social preferences.