Breeding status and ecology of the Martial Eagle in the Kalahari Gemsbok National Park,South Africa

Herholdt, J.J. & Kemp, A.C. 1997. Breeding status and ecology of the Martial Eagle in the Kalahari Gemsbok National Park. Ostrich 68 (24): 80–85.

The success of 16 nesting areas (territories) of Martial Eagles was monitored for seven successive years (1988–1994) in a protected area in the Kalahari desert of South Africa. Martial Eagles mostly laid in consecutive years (38 out of 53 attempts) and fledged, on average, 0.43 young/pair/year (38/88). Most Martial Eagles laid eggs in May and June (72.2%; n = 13 attempts). Almost all located Martial Eagle nests were in the Acacia erioloba savanna in the dry Auob and Nossob riverbeds. Martial Eagle nesting areas were spaced at intervals of 24.1 km (1144.6 km; n = 6) along the Nossob River, 15.1 km (8–34 km; n = 7) in the Auob River and 31.3 km (25–43 km, n = 4) in the interior dune area. A total of between 20 and 30 Martial Eagle pairs (20 known active nesting areas) occurred in the Kalahari Gemsbok National Park during the study period. There was no evidence of a decline in active nesting areas of Martial Eagles during the seven year study. There was no safe buffer zone around the Kalahari Gemsbok National Park and Martial Eagles were at times persecuted when foraging in the adjacent farmlands.     

Habitat preference, breeding success and the effect of primary productivity on Tawny Eagles Aquila rapax in the tropics

Breeding success of 176 Tawny Eagle pairs nesting on basalt (4724 km²– 92 pairs) and kalahari sand (9876 km²– 84 pairs) was monitored from 1973 to 1984 in Hwange National Park, Zimbabwe. Flat-topped trees were preferred for nesting but kalahari sand pairs used round-crowned trees more often, probably due to tree availability. Mean inter-nest distances on both biomes were significantly different (3–5 km on basalt, 59 km on kalahari sand). Clutch size and frequency of one-egg clutches in both biomes were similar and many more one-egg clutches were laid in the drier period of the study (1979–1984). There was no correlation between laying date and breeding success. More basalt pairs laid synchronously, probably due to the smaller inter-nest distances. Breeding success in both biomes was similar and significantly more chicks were reared during 1973–1978 than during 1979–1984 (wet and dry periods, respectively). Some districts produced more chicks than others, suggesting good and marginal areas within both biomes. The greater inter-nest distances and ability to breed successfully in round-crowned trees by kalahari sand Tawny Eagles resulted in a similar number of chicks reared per breeding attempt as basalt pairs, in spite of the lower primary production of the sand area.     

BREEDING BIOLOGY OF THE BATELEUR

Watson, R. T. 1990. Breeding biology of the Bateleur. Ostrich 61: 13–23.

Observations were made on the breeding biology of the Bateleur Terathpoius ecaudataus between 1981 and 1984, in the central region of the Kruger Nabonal Park. Nests were uniformly distributed with a mean inter-nest distance of 5,1 km and density of 3,1 nests/100km². Single-egg clutches were laid from January to June, and laying appeared to be suressed by unusually high rainfall events. The mean productivity was 0,47 young per pair per year, an a breeding failures were mainly due to failure to lay or predation. Breeding adults chaned nest sites within their territory on average once every 2,8 years, but territories and pairs were stable from year to year. Both members of a pair put equal time into care of the young.     

5. FURTHER NOTES UPON SAROTHRURA ELEGANS

Hustler, K. &; Howells, W. W. 1986. A population study of Tawny Eagles in the Hwange National Park, Zimbabwe. Ostrich 57: 101–106.

Tawny Eagle Aquila rapax breeding success has been monitored in the Hwange National Park, Zimbabwe from 1973–1984. There were 1044 breeding pair years with 640 chicks reared; an average of 0,61 chicks/breeding paid year. The average number of pairs breeding each year was 72,4%. Thirty-one percent of all breeding attempts failed; most during nest-building (59%). Rainfall in the latter part of the rainy season appeared to influence early and late laying pairs. Two-egg clutches were most common (76%) and 65% of all one-egg clutches laid failed to produce chicks. Several factors which may influence breeding success are discussed.     

Nest‐site characteristics,breeding success and competitive interactions between two recently sympatric apex predators

An influential period in avian life‐cycles is the annual breeding season, when competition over suitable nesting sites and territories is a key factor that can determine fitness and distribution, especially for species that are highly selective in their nesting habitats. We analysed nest‐site characteristics, breeding success and competitive interactions between two apex predator populations. Whereas the Short‐toed Eagle Circaetus gallicus has nested in the Judean Foothills (Israel) for a long time, the Long‐legged Buzzard Buteo rufinus has only invaded the nesting habitat of the Short‐toed Eagle during their breeding season in the last two decades. These two recently sympatric species have similar nesting ecology and frequently use the same nests. They are therefore expected to compete over nesting sites and territories. We analysed interspecific interactions between these two species by combining information from comprehensive observational, experimental, GIS analysis and remote sensing data, deriving 65 variables to characterize the nest‐sites used and the breeding success in 381 breeding attempts over four consecutive breeding seasons. To assess interspecific and intraspecific territorial behaviour and aggressiveness, stuffed Long‐legged Buzzards and Short‐toed Eagles were presented close to nests. Nest‐site characteristics overlapped substantially between species, and Long‐legged Buzzards occupied 21% of all Short‐toed Eagle nests. Intraspecific aggression rates among Long‐legged Buzzards were higher than their interspecific aggression rates with Short‐toed Eagles and also higher than intraspecific aggression among Short‐toed Eagles. Long‐legged Buzzard and Short‐toed Eagle breeding densities (1.59 ± 0.11 and 2.96 ± 0.11 pairs per 10 km², respectively) are likely to be the highest across their respective breeding distributions, with a maximum productivity of 0.96 ± 0.01 and 0.56 ± 0.05 (young fledged/breeding pair) for Long‐legged Buzzard and Short‐toed Eagle, respectively. Intraspecific interactions among both species play an important role in determining their breeding success and the spatial distribution of nesting sites. Our results suggest that interspecific competition over nesting sites and territories between both species, and the potential dominance of Long‐legged Buzzard, has both direct and indirect impacts on the spatial and demographic distribution of Short‐toed Eagles due to the recent establishment of Long‐legged Buzzard territories in the Judean breeding area.     

Comparative nest habitat characteristics of sympatric White‐tailed Haliaeetus albicilla and Golden Eagles Aquila chrysaetos in western Scotland

Capsule Golden and White‐tailed Eagles selected different habitats for nesting.

Aim To investigate differences in nesting habitat used by sympatrically breeding eagles in western Scotland, following reintroduction of White‐tailed Eagles from 1975 onwards.

Methods Nest‐site locations from national surveys in 2003–05 were entered into a geographical information system (GIS) in order to measure a set of geographic parameters for each nest site. Binary logistic regression with backwards deletion of non‐significant terms was used to derive minimum adequate models at two spatial scales of the likelihood of an eagle nest belonging to one species or the other. We compared changes in occupancy between 1992 and 2003 of Golden Eagle territories inside and outside a GIS model of potential White‐tailed Eagle habitat and according to proximity to White‐tailed Eagle nests.

Results White‐tailed Eagles nested at lower altitudes than Golden Eagles, in more wooded habitats with more open water close by, tending to nest in trees where these were present. There were 3359 km² of potential White‐tailed Eagle nesting habitat within 25 km of existing White‐tailed Eagle nests, containing 54 Golden Eagle territory centres, but we found no difference in change of occupancy for Golden Eagle territories close to White‐tailed Eagles compared with those further away.

Conclusion White‐tailed and Golden Eagles appear to partition nesting habitat in the west of Scotland by altitude. This corresponds with behaviour in western Norway and with the situation described in historical accounts of nest‐sites in western Scotland prior to extinction of White‐tailed Eagles. It is also consistent with recent studies showing little overlap in breeding season diet of Golden and White‐tailed Eagles in western Scotland, and likely partitioning of foraging habitat by altitude. We conclude that the likelihood of competitive exclusion is less than previously suggested.     

Using independent nest survey data to validate changes in reporting rates of Martial Eagles between the Southern African Bird Atlas Project 1 and 2

Repeat monitoring is vital to measure biodiversity change. However, monitoring protocols may change, as survey techniques improve or different questions are asked. Such modifications may cause difficulties when examining changes in wildlife populations. The Southern African Bird Atlas Project (SABAP) 1 and 2 are repeat national bird surveys undertaken 20 years apart. These surveys therefore offer unrivalled potential to examine bird population changes in an African context. However, changes in protocols, both spatially and temporally, between the two surveys have raised concerns over using these data to infer population changes. In this study we use independ- ent nest survey data to test whether changes in reporting rates of Martial Eagles in the Kalahari Gemsbok National Park between the two SABAP surveys were reflected in real change in numbers of nesting pairs. From 11 quarter degree squares (QDS), covering c. 8 000 km2, both SABAP and nest surveys suggested a near identical 44% decline. Levels of agreement were weaker at the individual QDS scale, although in 67% of cases the direction of change was the same using both surveys. These results suggest that comparisons in the reporting rates between SABAP 1 and SABAP 2 accurately reflect changes in the breeding population size of this species.     

Spatial distribution and breeding territories of Bonelli’s Eagle Aquila fasciata in the western Anti-Atlas Mountains,Morocco

The North African population of Bonelli’s Eagle Aquila fasciata (Vieillot, 1822) is limited to the south by the northern fringe of the Sahara Desert. This study provides the first data on the spatial distribution and density of breeding Bonelli’s Eagles in south-west Morocco, at the southern limit of their breeding distribution in the Western Palearctic. We used broad-scale sampling to investigate spatial patterns in occupancy of territorial pairs of Bonelli’s Eagles in an area of ～29 715 km2 in the western Anti-Atlas Mountains, southern Morocco, during 2016–2018. We found 28 nesting territories containing 40 used nests, heterogeneously distributed in areas of high topographic variation, from 60 to 1 890 m asl. The average nearest-neighbour nest distance was 14.12 ± 9.90 km and varied from 2.65 km in the north-west to 37.80 km in the pre-Saharan lands in the south-west portion of the study area. This work shows the importance of the western Anti-Atlas Mountains as one of the most significant strongholds of the species in Morocco. However, there is a need for systematic analyses of the different factors affecting the distribution of the species to implement conservation actions of this peripheral population.     

Madagascar Fish Eagle productivity in the Tsimembo-Manambolomaty Protected Area and surrounding habitat of western Madagascar

We monitored the productivity of the critically endangered Madagascar Fish Eagle Haliaeetus vociferoides inside and outside of the Tsimembo-Manambolomaty Protected Area (T-M PA), western Madagascar from 2010 to 2015. We recorded 14 breeding pairs inside and 13 outside T-M PA. The T-M PA and surrounding habitat hosted respectively 10 and six breeding polyandrous pairs, composed of one adult female and two adult males. During the six-year study period, 101 eggs were laid in nests in T-M PA of which 60 hatched and 58 young fledged. We recorded 62 eggs laid in nests outside the T-M PA of which 39 hatched and 36 young fledged. Productivity was similar at both sites, inside and outside T-M PA, with 0.84 (58/69) and 0.76 (36/47) fledgling per nesting attempt and 0.69 (58/84) and 0.5 (36/72) fledglings per territorial pair, respectively. Polyandrous pairs have higher productivity compared with normal pairs. Threats to Madagascar Fish Eagles and their habitat were low due to the existence of a community-based resource management system called the Local Management Secured System (GELOSE) inside and outside the T-M PA. This system is based on strengthening local traditional customs and rules, and involving local people in managing their natural resources sustainably along with biodiversity conservation.     

A 13-YEAR POPULATION STUDY OF THE BLACK EAGLES IN THEMATOPOS,RHODESIA, 1964–1976

Gargett, V. 1977. A 13-year population study of the Black Eagles in the Matopos, Rhodesia, 1964–1976. Ostrich 48:17-27.

The resident black Eagle Aquila verreauxi population in approximately 620 km² of the Matopos, Rhodesia, underwent changes from 1971 and appeared less stable than in the first five years. Six new territories were established in the National Park; two territories in Tribal Trust Land were abandoned; one territory in the National Park vacant for five years and one in Tribal Land vacant for at least 11 years were reoccupied. breeding data covering 13 years confirm the five-year findings. In 652 pair-years 442 breeding attempts were made with 339 young eagles f edging: a reproductive success rate of 0,52 young per pair per year. On average 68 % of the population bred every year, each pair attempted breeding in two years out of three, and one attempt in four was unsuccessful. Annual and individual variations in breeding performance were considerable, from 46% to 89% of the population breeding, and from two successes in six attempts for one pair to 12 successes in 12 attempts for two pairs. Over 13 years the percentage of the population breeding annually followed the form of a sine curve with a ten year period.

Fourteen factors that might affect annual and/or individual performance are considered. Below average rainfall years were followed by above average breeding; and generally fewer clutches were laid early after heavy rainfall in the three months preceding laying. Clutches laid late were less successful than those laid early. Breeding was affected by the proximity and intervisibility of nests, the previous year's performance and intraspecific disturbance. Appropriation of nests by other species prevented breeding and no new pair bred while establishing or re-establishing its territory. Building a new nest was followed by laying in the same season only if the nest was completed by mid-May, the peak laying period, building or partly building two nests in one season did not prevent breeding in the following year. At least 76% of clutches were c/2. The causes of two eaglets' deaths were ascertained and the remains of two adults were found. Pairs with territories in Tribal Trust Land had a significantly lower breeding performance than pairs in the protected National Park. Only traces of pesticide residues were found in four eggs. Observers' visits did not affect reproductive success.     

Ecological and environmental correlates of territory occupancy and breeding performance of migratory Golden Eagles Aquila chrysaetos in interior Alaska

Understanding relationships between environmental conditions and reproductive parameters is important when interpreting variation in animal population size. The northwestern North American population of Golden Eagles Aquila chrysaetos canadensis initiates courtship and nesting in early spring when prey diversity is low and weather conditions are severe. Snowshoe Hare Lepus americanus and Willow Ptarmigan Lagopus lagopus, the primary prey of Golden Eagles early in their nesting season in interior Alaska, both exhibit cyclical fluctuations in abundance, providing the opportunity to investigate such relationships. We used Bayesian hierarchical models to explore variation in territory occupancy, nesting rates, nesting success and productivity of Golden Eagles from 1988 to 2010 in Denali National Park and Preserve, Alaska, in relation to annual and site‐specific parameters including prey abundance, weather conditions, elevation and human activity. We also investigated the long‐term fluctuations of breeding performance over the course of the study. The abundance of Hares influenced both the number of Eagles that laid eggs and the number of Eagles that produced fledglings. The conditions on the breeding ground did not explain observed declines in nesting rates and fledgling production, suggesting that other factors such as change in the age structure of the population, increased intraspecific competition or deterioration of migration and wintering habitat are driving the long‐term trends of these parameters.     

DISPERSION, BREEDING AND PREY OF THE HEN HARRIER CIRCUS CYANEUS IN GLEN DYE, KINCARDINESHIRE

Hen Harriers were studied on a grouse moor in northeastern Scotland from 1970-74. Numbers in spring were fairly stable, and the 24 nesting territories occupied in 1974 were regularly dispersed with a mean nearest neighbour distance of 1.52 ± s. e. 0.09 km. Many pairs apparently failed to breed and left the area. The mean clutch size of those remaining was 4.70 ± s. e. 0.24 (n= 27) and the mean number of young fledged per successful nest was 3.11 ± s. e. 0.26 (n= 19). Young males were more likely to disperse far from the study area than young females. The variety of prey species observed from hides at five nests was very limited, and comprised mainly pipits, grouse chicks and lagomorphs. Estimates by weight suggest that grouse and lagomorphs accounted for 89% of all prey. Males brought more small items and fewer large items to nests than females, and on average provided 72% of all prey items seen during watches from the hides. On the basis of studies of prey at three nests in 1974, and counts of grouse in spring and late summer, harrier predation was estimated to have reduced the number of grouse which might otherwise have survived to late July that year by a maximum of 7.4%.     

THE INFLUENCE OF RAINFALL ON BLACK EAGLE BREEDING OVER 31 YEARS IN THE MATOBO HILLS,ZIMBABWE

Gargett, V., Gargett, E. & Damania, D. 1995. The influence of rainfall on Black Eagle breeding over 31 years in the Matobo Hills, Zimbabwe. Ostrich 66: 114–121.

The effect of rainfall from 1964 to 1994 on the annual reproductive rate and number of resident pairs of Black Eagles Aquila verreauxii in the Matobo Hills, Zimbabwe, and on the abundance of their staple prey, hyrax, Procavia capensis and Heterohyrax brucei is reviewed. The number of resident pairs of Black Eagles increased with increased rainfall, when hyrax numbers were estimated to be at a very high level. Subsequent poor rainfall years coincided with a decrease in the number of resident pairs, a smaller proportion of pairs breeding, a lower reproductive rate and a dramatic decline in prey numbers.     

Adaptive habitat preferences in the Tawny Owl Strix aluco

Capsule: Tawny Owls Strix aluco occupying nest boxes preferred habitats which were positively associated with the probability of nesting success.

Aims: We aimed to determine whether or not: (1) Tawny Owls showed habitat preferences when occupying nest boxes; (2) nesting performance was related to the habitats around occupied nest boxes and (3) habitat availability had changed around available and occupied nest boxes between 1995–2004 and 2005–14.

Methods: Tawny Owls were studied using nest boxes erected in a commercial forest. During nest boxes checks (724 cases), data on occupancy and nesting performance (88 cases) were recorded, and habitat within a 0.4?km radius around nest boxes was analysed.

Results: Tawny Owls had preferences for clearings within forests, mature forests and grasslands but avoided young forests. We found a positive relationship between nesting success and abundance of clearings within the forest, and a negative relationship between nesting success and abundance of young forests. A change in habitat preferences over the two decades was evident, but habitat availabilities remained similar.

Conclusions: Findings indicate adaptive habitat selection in Tawny Owls because preferred habitats were associated with higher fitness and this type of habitat became more frequently selected over time.     

Effects of age,territoriality and breeding on survival of Bonelli’s Eagle Aquila fasciata

Survival typically contributes most to population trends in long‐lived birds and its accurate estimation is therefore vital for population management and conservation. We evaluated the effects of age, territoriality and reproduction on survival in Bonelli’s Eagle Aquila fasciata through multistate capture‐mark‐recapture analyses on a long‐term dataset. Monitoring was carried out in southeast France (1990–2008) and involved the surveying of territorial Eagles, the marking of fledged chicks, and the recording of resightings and recoveries of marked non‐territorial and territorial birds. Survival improved with age, but territoriality was not retained in the best model; yearly survival was estimated at 0.479 for fledglings (to 1 year of age), 0.570 for 1‐ and 2‐year‐olds, and 0.870 for 3‐year‐old and older individuals. The second best model supported a further increase in survival from 3‐year‐olds (0.821) to older individuals (0.880). In the third best supported model, territoriality enhanced survival, but only in 2‐year‐olds (0.632 vs. 0.562 for non‐territorial). We found no correlation between the previous breeding stage and future survival, consistent with the long lifespan of the study species. Nevertheless, 4‐year‐old and older successful breeders were more likely to breed the following year than failed adult breeders (0.869 vs. 0.582), suggesting that the cost of reproduction is small in comparison with the variation in quality among individuals or their territories.     

Density dependence in Golden Eagle Aquila chrysaetos fecundity better explained by individual adjustment than territory heterogeneity

Density-dependence effects acting on fecundity can be explained by two competing hypotheses. The individual adjustment hypothesis (IAH) states that, as population density increases, interference among individuals negatively affects their breeding performance. The second hypothesis, the habitat heterogeneity hypothesis (HHH), proposes that, as more individuals occupy the space available, lower quality habitats are increasingly used, causing average population fecundity to decline. In territorial species, it is often predicted that interference mechanisms (IAH) should be of less importance than spatial heterogeneity (HHH). Here, we test this prediction in Golden Eagles, using 35 years of reproduction monitoring data from a population that has been recolonizing the grounds of a French National Park (Ecrins) in the Alps. During the study period, the Eagle population increased from c. 11 to 41 territorial pairs, providing a good opportunity to explicitly assess fecundity across a gradient of densities. Under the IAH, we expect the fecundity of all territories to diminish as density rises. Under strict HHH, older territories should maintain higher fecundity across time, and a positive relationship between fecundity and the seniority of a territory should be observed. A density-dependent pattern was clearly detected at the population level. At the territory level, the decrease of fecundity was strongly related to population size but not to territory seniority. Fecundity decreased similarly in all territories, suggesting that the IAH better explains the observed pattern. Two alternative mechanisms, related to the IAH, could be at play in this population: (1) negative interference by neighbours and non-territorial Eagles and (2) the contraction of individual territories over time. Our results provide new insights into density dependence in territorial raptors, suggesting that, in addition to habitat heterogeneity, interference mechanisms might actually also play an important role.     

Movements by juvenile and immature Steller's Sea Eagles Haliaeetus pelagicus tracked by satellite

Twenty‐four juvenile Steller's Sea Eagles Haliaeetus pelagicus were tracked via satellite from natal areas in Magadan, Kabarovsk, Amur, Sakhalin and Kamchatka. Nestling dispersal occurred between 9 September and 6 December (n = 24), mostly 14 September–21 October, and did not differ among regions or years. Most eagles made stopovers of 4–28 days during migration. Migration occurred 9 September–18 January, mostly along previously described routes, taking 4–116 days to complete (n = 18). Eagles averaged 47.8 km/day excluding stopovers; 22.9 km/day including stopovers. The mean degrees of latitude spanned during migration was: Kamchatka, 2.1; Magadan, 11.6; Amur, 7.3; and Sakhalin, 1.1. Eagle winter range sizes varied. Eagles concentrated in 1–3 subareas within overall winter ranges. The mean size of the first wintering subareas was 274 km², the second 529 km², and the third 1181 km². Second wintering areas were south of first wintering areas. Spring migration started between 2 February and 31 March. Two eagles from Magadan were tracked onto summering grounds, well south of their natal areas. Both had early and late summering areas. One bird was followed for 25 months. It initiated its second autumn migration in the first half of October and arrived on its wintering grounds on 26 December. The second autumn migration covered 1839 km (20.9–22.4 km/day). Unlike its first winter when it used two subareas, this bird used only one subarea in 1998–99, but this was located near wintering areas used in 1997–98. It left its wintering ground between 13 April and 13 May, and arrived on its summering grounds between 7 June and 8 July. Unlike most satellite radiotracking studies, data are presented from a relatively large number of birds from across their breeding range, including new information on eagle movements on the wintering grounds and during the second year.     

Does variation of sex ratio enhance reproductive success of offspring in tawny owls (Strix aluco)

Tawny owls, Strix aluco, laid female-biased clutches on territories with more abundant prey (field voles) in June, the month that chicks fledge. This appeared to enhance the subsequent reproductive success of fledglings, as in 1995 there was a significant correlation between the number of chicks fledged by adult females and the June vole abundance in the territory on which they were reared as chicks. This relationship did not hold for males. Since tawny owls lay eggs in March, these results indicate that owls are able to predict the June vole numbers on their territory, and respond by producing more of the sex most likely to gain a long-term benefit when resources are good.     

Southern kalahari phytosociology

Summary The vegetation of the Kalahari Gemsbok National Park, which lies in the centre of the semi-arid Southern Kalahari, was studied. This area is considered to be largely representative of the Southern Kalahari in general. The region is covered by a layer of red sand piled into dunes. Two large dry river-beds cross the area and numerous pans occur. Calcrete outcrops are found along rivercourses and around pans. The vegetation is generally an extremely open shrub or tree savanna and phytogeographically the area is regarded as belonging to the Karoo-Namib Region. 132 quadrats, most of which covered 100 m², were studied and the vegetation is classified according to the Zürich-Montpellier method. The physiognomy of all phytocoenoses was determined according to the system ofFosberg (1967). A striking correlation was found between plant communities and the four main habitats: sand, calcrete, pans and river-beds. Twelve syntaxa were recognized, eight of these are described as associations and one as a subassociation. They are as follows:— 1. On sand: Stipagrostietum amabilis (with subass. terminalietosum) found on dune crests, Hirpicio echini-Asthenatheretum on more compact red sand in dune valleys, Monechma incanum-Stipagrostis ciliata (two communities) on pink to whitish sand, Peliostomo-Stipagrostietum obtusae on whitish compact sand; 2. On calcrete: Aizoo-Indigoferetum auricomae; 3. On pans and pan-like formations: Sporobolo lampranthi-Zygophylletum tenuis on pan-like alluvial flats in the Nossob rivercourse, Sporoboletum coromandelianion the central parts of pans, Sporoboletum rangei along the periphery of pans and on sand accretions on the pan surface, Lycium tenue community on small loamy sand accretions on pans or in river-beds; 4. In river-beds: Panicetum colorati. Life form spectra based on total cover-abundance values are given. Differences in the spectra of various communities are briefly discussed with reference to their habitats. Therophytes were shown to be the most important life form in all syntaxa except the Sporoboletum rangei. The vegetation exhibits a very marked zonation and a sequential relationship between communities is demonstrated.

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Zusammenfassung Die Vegetation des Kalahari Gemsbok Nationalparks, welcher im Zentrum der semi-ariden Südlichen Kalahari gelegen ist, wurde untersucht. Der Park wird als weitgehend typisch für die gesamte Südliche Kalahari betrachtet. Das Gebiet wird von einer Sandschicht bedeckt die zu Dünen aufgeworfen ist. Zwei grosse Flussbetten durchqueren das Gebiet und zahlreiche Pfannen werden angetroffen. Oberfl?chenkalk kommt l?ngs den Flussl?ufen und um Pfannen herum vor. Die Vegetation ist im allgemeinen eine extrem offene Strauch- oder Baumsavanne und phytogeographisch wird das Gebiet zur Karoo-Namib Florenregion gerechnet. 132 Relevés, von denen die meisten eine Oberfl?che von 100 m² hatten, wurden aufgenommen, und die Vegetation wurde nach der Zürich-Montpellier-Methode klassifiziert. Die Physiognomie aller Phytoz?nosen wurde nach dem System vonFosberg (1967) bestimmt. Eine auffallende Wechselbeziehung zwischen Pflanzengesellschaften und den folgenden vier wichtigsten Standorten wurde festgestellt: Sand, Kalk, Pfannen und Flussbetten. Zw?lf Syntaxa wurden erkannt, wovon acht als Assoziationen und eine als Subassoziation beschrieben werden. Sie sind die folgenden: (1) Auf Sand: Stipagrostietum amabilis (mit Subass. terminalietosum) auf Dünenk?mmen, Hirpicio echini-Asthenatheretum auf kompakterem roten Sand in Dünent?lern, Monechma incanum-Stipagrostis ciliata (zwei Gesellschaften) auf rosa bis weisslichem Sand, und Peliostomo-Stipagrostietum obtusaeauf weisslichem kompaktem Sand; (2) Auf Oberfl?chenkalk: Aizoo-Indigoferetum auricomae; (3) Auf Pfannen und pfannenartigen Formationen: Sporobolo lampranthi-Zygophylletum tenuis auf pfannenartigen Alluvialfl?chen im Flusslauf des Nossob, Sporoboletum coromandeliani im Zentrum von Pfannen, Sporoboletum rangei auf Pfannenr?ndern und auf Sandanh?ufungen auf Pfannenoberfl?chen, Lycium tenue-Gesellschaft auf kleinen lehmigen Sandanh?ufungen auf Pfannen oder in Flussbetten; (4) In Flussbetten: Panicetum colorati. Lebensformspektren, die auf Artm?chtigkeitswerten basieren, sind in Diagrammen für die verschiedenen Syntaxa zusammengestellt. Unterschiede zwischen den Spektren der verschiedenen Gesellschaften werden besprochen mit Bezug auf ihre Standorte. Therophyten sind in allen Syntaxa, mit Ausnahme des Sporoboletum rangei, die wichtigste Lebensform. Die Vegetation l?sst deutliche Zonierung erkennen. Es wird gezeigt in welcher wechselseitigen Beziehung die Gesellschaften zueinander stehen.