Contextual Factors Meditating Contests Between Male Chacma Baboons in Botswana: Effects of Food,Friends and Females

We examined aggressive displays among male chacma baboons (Papio ursinus) over a 23-mo period in the Okavango Delta of Botswana. High-ranking males were more likely than middle- or low-ranking males to participate in displays. Regardless of rank, all males were more likely to participate in chases or physical fights if their opponents rank was similar to their own. Most chases and fights, including those that led to injuries, were also between similarly-ranked males. The rate of both aggressive displays and approach-retreat interactions increased in the weeks before rank reversals, suggesting that rank challenges were preceded by a period when males assessed each others competitive ability and/or motivation. Aggressive displays between disparately-ranked opponents occurred most frequently in contests involving resources of high fitness value: the defense of meat, the defense of estrous females, and the protection of infants against infanticidal attacks. Silent displays were more likely to occur in these three contexts than were displays that occurred as part of more slowly escalating interactions, in which opponents first exchanged calls. Results suggest that competitive encounters among male baboons follow patterns predicted by evolutionary game theory.     

Affiliation Among Females in Wild Hamadryas Baboons (Papio hamadryas hamadryas)

Previous researchers of hamadryas baboons have described a star-shaped sociogram, whereby the strongest social bonds within hamadryas one-male units are between a leader male and his females and bonds among females are weak by comparison. This type of social organization is also known as cross-bonding to distinguish it from the female-bonding found in most papionin monkeys. Models of female primate socioecology suggest that hamadryas baboons lack female bonding due to their reliance on scarce, widely-dispersed food resources. Here, I report observational data from a wild population of hamadryas baboons in Ethiopia indicating that, while females varied widely in their frequency of social interaction with other females, most females spent about as much social time with other females as they did with the leader male and some females even crossed unit boundaries to interact with one another. The size of a unit was positively correlated with the tendency of its females to interact with other females and was negatively correlated with the tendency of its females to interact with the leader male. Females were equally likely to spend social time with other females whether or not the leader male was available for social interaction at the time. Overall, this study suggests that a star-shaped sociogram does not characterize all hamadryas baboons and that female hamadryas may be, to some extent, female-bonded as well as cross-bonded. The lack of more pronounced female bonding in hamadryas is probably due to the behavior of males rather than to ecological factors.     

Land-use and resource conflicts in the Okavango Delta, Botswana

This study assesses land-use conflicts in the Okavango wetland ecosystem. A survey of the livelihood activities of a sample of four villages has been carried out and a stakeholder approach used to identify and analyse the key actors involved in resource competition and conflicts in the area. Traditional and emerging stakeholders were identified and found to be in conflict not only with each other but within themselves. Institutional policies on land use in the area are not properly harmonized, and there has been a top-down approach to development planning and implementation of development programmes. As a result, land-use conflicts have escalated in the area. The Okavango Delta Management Plan adopted in 2007 should integrate and harmonize all the land-use policies, and land management in the area.     

Surface water quality in the Okavango Delta panhandle,Botswana

The Okavango Delta, a Ramsar and a World Heritage Site, is an important source of food and water in the Kalahari Desert of southern Africa. Although the eastern delta fan is a protected area, the rest, including the upstream panhandle, is unprotected. Water quality in the Okavango Delta panhandle from Popa Falls, Namibia, to lagoons in the north-western delta fan, was investigated between December 2006 and January 2009. Results were compared to those of a study undertaken in the lower panhandle in the mid-1980s, in order to identify changes, if any. Despite increased human activities and livestock, physical water quality parameters lay within the ranges set out in the water quality guidelines of South Africa, while most chemical substances were below detection limits. The microbiological water quality indicated that microbial concentration was highest in areas of increased human and livestock activity. In general, the water quality of the unprotected panhandle had remained unaltered after more than two decades of change and growing pressure on it.     

Nutrient Budget in the Seasonal Wetland of the Okavango Delta, Botswana

The nutrient (P and N species) and chloride budgets were investigated in a representative floodplain in the seasonal wetlands of the Okavango Delta, Botswana. A variety of sources of nutrients in the surface water were considered, namely ion species coming with the floodwater, those generated from dry floodplain soils and those from water-soluble dust deposition (both local and long-range sources). Concentrations of total-nitrogen and chloride in surface water were below 1 mg l⁻¹. Total-phosphorus concentrations were 0.05 mg l⁻¹, reflecting the oligotrophic character of the system. Dust deposition rates were highest for chloride at 2.44 g m⁻² year⁻¹ followed by 0.79 g m⁻² year⁻¹ for total-N, 0.40 g m⁻² year⁻¹ for ammonia and only 0.02 g m⁻² year⁻¹ for total-P, respectively. Chloride was derived primarily from long-range transport, while N and P species were of more local origin. Dissolution rates for these ions combined were calculated to be 3.9 g m⁻² for the flooded area in the 1999 season and thus all dry deposits must be re-dissolved. The accumulation of dust deposits on dry surfaces and their subsequent dissolution causes 2–5 times higher concentrations of nitrogen, phosphorus and chloride with the onset of the flood, thus boosting the nutrient stock in the crucial phase of the onset of flooding. Chloride dissolved from dry soil surfaces and dust contributed approximately 40% to the overall floodplain budget. Although contributions from the soil surface and dust to the nitrogen and phosphorus pools of the floodplain are less prominent (with 10% of total), they nonetheless represent a significant source of nutrients in the entire system. Extrapolation to annually flooded swamps (10,000 km²) indicates a maximum contribution of 40% for total-nitrogen and 60% for total-phosphorus from dust deposition on wet or dry surfaces to the nutrient pool of the water body.     

Pesticide levels in stork and spoonbill eggs from the Okavango Delta,Botswana

Motalaotte, S. & Bouwman, H. 2000. Pesticide levels in stork and spoonbill eggs from the Okavango Delta, Botswana. Ostrich 71 (1&2):344.

Ecotourism in the Okavango Delta is one of the major sources of foreign revenue for the Republic of Botswana. Promoting this region is therefore vital to sustainable development. One of the concerns was the past use of organochlorine pesticides to combat tsetse fly. This study looked at the levels and possible risk this use poses to Marabou storks and African Spoonbills, as well as some other birds, from this region. One particular breeding colony also experienced a decline in breeding success, the cause of which is unknown. DDE was present in almost all the eggs and blood sampled, while DDD, DDT and Dieldrin were also found in many. These pesticides are therefore present in the food chain and should be closely monitored to determine any temporal trends.     

Community ecology and conservation of the fishes of the Okavango Delta,Botswana

Synopsis The Okavango Delta is a large inland swamp in northern Botswana which receives an annual flood from the highlands of southern Angola. There are distinct fish taxocenes in the Okavango which can be separated from each other by the physical characteristics of the different habitat types with which they co-evolved. An account is given of the ecology and conservation of the fishes of the Okavango Delta. Their response to the annual flood regime, and the environmental factors that limit their distribution and abundance, are described. In the northern riverine floodplain and perennial swamp a higher species richness and ichthyomass was recorded than in the seasonal swamp and drainage rivers. Suggestions are made on the conservation of Okavango fishes taking into account the ecological characteristics of the Delta.     

Nest niche dynamics of Meyer's Parrot Poicephalus meyeri in the Okavango Delta,Botswana

Meyer's Parrot Poicephalus meyeri is the only cavity-nesting bird species that breeds during winter in the Okavango Delta. This is facilitated by exclusive access to arthropod larvae incubating inside and feeding on fruits and pods in their diet. To minimise predation risk and overcome low overnight temperatures they have specialised, non-random nest cavity preferences that restrict them to 4.5% of the available nest cavities in the study area. Here we evaluated the nest niche of Meyer's Parrot by studying the nest tree preferences and ecological context of all nest cavities to determine factors that may restrict breeding success in disturbed or altered habitat. Although specific nest tree preferences were significantly different between host tree species, Meyer's Parrot preferred trees greater than 14 m in height that were in relatively poor condition (e.g. portion of the canopy dead). A comparison of nest tree characteristics (n = 75) and the availability of these tree specifications in a representative sample of the different habitat types (n = 1 129) within the sample area indicated that Meyer's Parrot are dependent on riverine forest, Acacia-Combretum marginal woodland and dry mopane woodland for nesting opportunities. Disturbance to hardwood trees by African elephants Loxodonta africana and fungal attack (e.g. Coriolus versicolor) are likely important dynamics in supporting healthy Meyer's Parrot populations and cavity-nesting bird communities.     

A vegetation-based hierarchical classification for seasonally pulsed floodplains in the Okavango Delta,Botswana

A classification scheme is presented for seasonal floodplains of the Boro-Xudum distributary of the Okavango Delta, Botswana. This distributary is subject to an annual flood-pulse, the inundated area varying from a mean low of 3 600 km² to a mean high of 5 400 km² between 2000 and 2006. A stratified random sample of 30 sites was surveyed for species composition and abundance in March–June 2007, using multiple quadrats along transects orthogonal to the floodplain long axis. A combination of indicator species analysis and ordination was used to derive a hierarchical classification system for floodplains, based on species assemblages. Indicator species analysis was used to identify ecologically meaningful levels of division, at four and nine classes. The four main classes of floodplain were: (1) Dry Floodplain Grassland (main indicators Urochloa mosambicensis, Ipomoea coptica, Chloris virgata and Pechuel-Loeschea leubnitziae); (2) Seasonally Flooded Grassland (Nicolasia costata, Eragrostis lappula, Cyperus sphaerospermus and Setaria sphacelata); (3) Seasonally Flooded Sedgeland (Eleocharis dulcis, Leersia hexandra, Oryza longistaminata and Cyperus articulatus); and (4) Seasonal Aquatic Communities (Sacciolepis typhura, Eleocharis variegata, Fuirena pubescens and Cycnium tubulosum). The resultant dendrogram provides an objective routine for classifying floodplains in the Boro-Xudum distributary in an ecologically meaningful way. This classification will assist in monitoring changes in vegetation resulting from hydrological change.     

Spatial and temporal dynamics of diffusive methane emissions in the Okavango Delta,northern Botswana,Africa

Global warming is associated with the continued increase in the atmospheric concentrations of greenhouse gases; carbon dioxide, methane (CH₄) and nitrous oxide. Wetlands constitute the largest single natural source of atmospheric CH₄ in the world contributing between 100 and 231 Tg year^?1 to the total budget of 503–610 Tg year^?1, approximately 60 % of which is emitted from tropical wetlands. We conducted diffusive CH₄ emission measurements using static chambers in river channels, floodplains and lagoons in permanent and seasonal swamps in the Okavango Delta, Botswana. Diffusive CH₄ emission rates varied between 0.24 and 293 mg CH₄ m^?2 h^?1, with a mean (±SE) emission of 23.2 ± 2.2 mg CH₄ m^?2 h^?1 or 558 ± 53 mg CH₄ m^?2 day^?1. These emission rates lie within the range reported for other tropical wetlands. The emission rates were significantly higher (P < 0.007) in permanent than in seasonal swamps. River channels exhibited the highest average fluxes at 31.3 ± 5.4 mg CH₄ m^?2 h^?1 than in floodplains (20.4 ± 2.5 mg CH₄ m^?2 h^?1) and lagoons (16.9 ± 2.6 mg CH₄ m^?2 h^?1). Diffusive CH₄ emissions in the Delta were probably regulated by temperature since emissions were highest (20–300 mg CH₄ m^?2 h^?1) and lowest (0.2–3.0 mg m^?2 h^?1) during the warmer-rainy and cooler winter seasons, respectively. Surface water temperatures between December 2010 and January 2012 varied from 15.3 °C in winter to 33 °C in summer. Assuming mean inundation of 9,000 km², the Delta’s annual diffusive emission was estimated at 1.8 ± 0.2 Tg, accounting for 2.8 ± 0.3 % of the total CH₄ emission from global tropical wetlands.     

River-wetland interaction and carbon cycling in a semi-arid riverine system: the Okavango Delta, Botswana

The Okavango River, in semi-arid northwestern Botswana, flows for over 400 km in a pristine wetland developed on a large (>22,000 km²) alluvial fan (Okavango Delta). An annual flood pulse inundates the floodplains of the wetlands and travels across the Delta in 4–6 months. In this study, we assess the effects of long hydraulic residence time, variable hydrologic interaction between river–floodplain–wetland and evapotranspiration on carbon cycling. We measured dissolved inorganic carbon (DIC) concentrations and stable carbon isotopes of DIC (δ¹³C_DIC) from river water when the Delta was not flooded (low water) and during flooding (high water). During low water, the average DIC concentration was 31 % higher and the δ¹³C_DIC 2.1 ‰ more enriched compared to high water. In the lower Delta with seasonally flooded wetlands, the average DIC concentration increased by 70 % during low water and by 331 % during high water compared to the Panhandle with permanently flooded wetlands. The increasing DIC concentration downriver is mostly due to evapoconcentration from transpiration and evaporation with increased transit time. The average δ¹³C_DIC between low and high water decreased by 3.7 ‰ in the permanently flooded reaches compared to an increase of 1.6 ‰ in the seasonally flooded reaches. The lower δ¹³C_DIC during high water in the permanently flooded reaches suggest that DIC influx from the floodplain-wetland affects river’s DIC cycling. In contrast, higher river channel elevations relative to the wetlands along seasonal flooded reaches limit hydrologic interaction and DIC cycling occurs mostly by water column processes and river-atmospheric exchange. We conclude that river-wetlands interaction and evapoconcentration are important factors controlling carbon cycling in the Okavango Delta.     

Pack-hunting in two species of catfish, Clavias gariepinus and C. ngamensis, in the Okavango Delta, Botswana

During the annual drawdown in the Okavango Delta, Botswana, large shoals of catfish migrate upstream in the main river channels. The examination of samples of the sharptooth catfish Clarias gariepinus and blunttooth catfish C. ngamensis revealed that they were pack-hunting and selectively preying on two species of mormyrids, the bulldog Marcusenius macrolepidotus and the churchill Petrocephalus catostoma . The predation on mormyrids may be related to prey size and abundance. In addition, catfish may sense the electrical discharge given off by the mormyrids when disturbed. The catfish feed intensively for a few months and build up body reserves and reproductive condition prior to spawning on shallow floodplains with the onset of the annual floods from Angola.     

The reproductive biology and early development of the African pike,Hepsetus odoe,in the Okavango Delta,Botswana

Synopsis The reproductive biology of the African pike,Hepsetus odoe, was studied over a four-year period in the Okavango Delta, Botswana. Spawning takes place between August and May in different parts of the Delta. Fish in the seasonal swamp and drainage rivers have a truncated spawning season between August and January, while those in the perennial swamp have an extended spawning season from September to May. The variation in spawning season appears to be associated with the degree of environmental perturbation brought about by the annual flood cycle. Male and female pike mature at 140 and 160 mm standard length (SL) respectively. Females predominate in the population and produce an average of 6440 eggs per season and are multiple spawners. The number of eggs per spawning averages about 2630. The eggs are deposited in a foam nest which is guarded by the parents. Newly hatched embryos suspend themselves below the nest via a cement gland and remain in the vicinity of the spawning site until they have reached a relatively advanced stage in their development. The larval period is relatively short which implies that this species undergoes nearly a direct development. Foam nests appear to be a predator avoidance mechanism as well as an adaptation to fluctuating oxygen and water levels. The initiation of the spawning season is more closely associated with water temperature than with the annual flood cycle which appears to be more important in regulating the size of the spawning stock.     

Male Influx, Infanticide, and Female Transfer in Macaca radiata radiata

In bonnet macaques, males usually disperse between groups and females remain philopatric, but researchers have reported female transfer. We report a rare case of male influx during the mating season in our bonnet macaque study group in the Anaimalai Hills. The density of bonnet macaques in the study region was unusually high. The study group had a single, crippled adult male with a long tenure and 5 adult females. During the mating season, adult females approached and mated with outgroup males, and then several males entered the group. The adult male left the group without any resistance. The incoming males mated with 3 receptive females, forcibly mated with 2 lactating females, and attacked and killed 2 infants. During the influx, 2 outgroup females joined the group. The data suggest that male influxes provide an opportunity for infanticide and female transfer, which can have important fitness consequences even in species in which they rarely occur.     

Environmental change over two decades since dredging and excavation of the lower Boro River, Okavango Delta, Botswana

The Okavango Delta, southern Africa's largest wetland, is situated on the fringe of the semi-arid Kalahari Desert. It is a large alluvial fan, occupying a graben structure which is an extension of the East African Rift system. Of the 16 km³ of water which enters the Delta each year, 96% is lost to the atmosphere by evapotranspiration, 2% to groundwater and only 2% leaves as surface flow. In order to increase surface outflow to meet human needs, the distal Boro channel–floodplain system was dredged, excavated and bunded between 1971 and 1974. The immediate impact of these measures was the destruction of in-channel flora. After 20 years, the aquatic flora has recovered in the excavated channel. However, little recovery has occurred along the channel reach which was dredged. Moreover, there has been significant encroachment of terrestrial species onto the floodplain in the region of the dredged channel. In addition, dredging created a nick point which has been migrating upstream by headward erosion since dredging ceased. The average rate of advance of the nick point has been about 500 m per year. Incision associated with nick point migration has produced a channel which is indistinguishable in form from the dredged channel and, like the dredged channel, is almost completely devoid of in-channel aquatic flora. The adverse environmental impact of dredging has therefore continued to propagate in an upstream direction, although the height of the nick point has decreased, suggesting a natural attenuation process. This is likely to result in eventual elimination of the nick point.