Gonadesiklus van die kroonkiewiet Vanellus coronatus op enkele binnelandse lughawens

Ondersoek is ingestel na die gonadesiklus van 474 kroonkiewiete Vanellus coronatus wat gedurende 1986/87 op twee binnelandse lughawens versamel is. Geoordeel aan die ovariummassa en deursnit van die grootste sigbare follikel vind ’n opvallende aktiwiteitspiek in die ovariumsiklus van wyfies gedurende die voorsomer plaas. Geoordeel aan die massa, volume, histologiese ontwikkelingstadia en saadbuisdeursnit van die testes kom ’n ooreenstemmende maar langer aktiwiteitspiek ook by mannetjies voor. Hoewel die testes van onvolwasse mannetjies oor die algemeen kleiner is as dié van volwassenes, is sommige individue binne hul eerste lewensjaar potensieel tot voortplanting in staat. Klaarblyklik word die broeisiklus van die kroonkiewiet in ’n groter mate deur die relatiewe beskikbaarheid van voedsel as omgewingsfaktore soos daglengte, temperatuur of reënval beïnvloed.English Title: Gonadal cycle of the crowned plover Vanellus coronatus at two inland airportsEnglish AbstractGonadal cycle of the crowned plover Vanellus coronatus at two inland airports. The gonadal cycle of 474 crowned plovers Vanellus coronatus collected from two inland airports during 1986/87 was investigated. Judged by the ovarian mass and the diameter of the largest visible follicle, a prominent activity peak occurs in the ovarian cycle of females during early summer. Judged by the mass, volume, histological development stages and diameter jof the seminiferous tubules of the testes, a corresponding but longer activity peak also occurs among males. Although the testes of immature males are generally smaller than those of adults, some individuals are potentially capable of reproduction within their first year of life. Evidently the breeding cycle of the crowned plover is influenced to a greater extent by the relative availability of food than by environmental factors such as day length, temperature or rainfall

Factors affecting the seasonal movements of Cape mountain zebras in the Mountain Zebra National Park

Factors underlying the movement of mountain zebras from a plateau in the summer to hill slopes and ravines in the winter were investigated. The movement was associated with a relative change in diet quality (as indicated by crude protein contents of preferred food plants and of the faeces) between the summer and winter habitats. In summer faecal and grass protein contents were higher in samples collected on the plateau than in those collected on the hill slopes. In the winter the reverse was the case. On the plateau the cover of grasses in the height range favoured by zebras changed only slightly from summer to winter. It thus seemed unlikely that the movement of zebras was caused by a seasonal change in the height structure of the grass sward. The diet comprised mostly grasses but traces of dicotyledons in the faeces were found more frequently during winter than summer

The Kuiseb river as a linear oasis in the Namib desert

The importance of the Kuiseb river as a linear oasis for larger mammals in the Namib desert, Namibia, was investigated over a period of three years. Following seasonal flooding the river dries rapidly confining consumable water to irregularly spaced pools which decrease in number and surface area as the dry season progresses. Compared to the lower sections of the river more water and less vegetation are available in the relatively inaccessible upper parts of the canyon, and vice versa. Based on direct observations and tracks at waterholes more mammals visit the lower than the upper sections of the river. Indications are that the pronounced seasonal influx of gemsbok Oryx gazella into the riverbed, presumably from the surrounding dune fields, is primarily dictated by the availability of water. The riverine habitat of the Kuiseb is therefore a resource critical to the survival of at least part of the central Namib ungulate population.Articl

Convergence and divergence in prey of sympatric canids and felids: Opportunism or phylogenetic constraint?

Since the canids and felids diverged in the mid-Eocene or earlier, each family has developed a suite of morphological and behavioural adaptations for obtaining and consuming prey. We here distinguish between prey taxa captured and eaten as a result of these phylogenetic adaptations, and those because they are fortuitously encountered, and argue that such supplementary prey, often opportunistically caught, create a buffer between sympatric, and potentially competitive, canids and felids and thus enhance coexistence. We base our analysis on dietary data derived from the stomach contents of four sympatric canid and felid species in the Free State Province, South Africa (canids: Cape fox Vulpes chama and black-backed jackal Canis mesomelas; felids: African wild cat Felis silvestris lybica and caracal Caracal caracal), and from results of studies on these species elsewhere in southern Africa. The two canid species preyed heavily on invertebrates, and thus opportunistically, while the felids (especially the caracal) concentrated on mammals, prey they are phylogenetically adapted to capture. Only three species of mammalian prey are shared by the four species. The ratio of opportunistically-to-phylogenetically mediated prey taxa used (the O/P ratio) differ between the species, with the black-backed jackal having the most opportunistically caught taxa in its diet, and the caracal the least. As predicted, a comparison of this data with those from dietary studies of the same species carried out elsewhere indicates that the number of opportunistically obtained prey taxa varies more than those resulting from phylogenetic adaptations. The largest canid had the widest food spectrum (35 prey taxa) while the smallest felid had the most restricted one (11 prey taxa). We argue that using the O/P distinction allows a better understanding of changes in food niche breadth of particular species, especially in xeric areas, and gives a better indication of possible exploitative competition for food by sympatric carnivores than when regarding all prey taxa as actively pursued. © 2004 The Linnean Society of London.Articl

Faecal helminth egg and oocyst counts of a small population of African lions (<i>Panthera leo</i>) in the southwestern Kalahari, Namibia : research communication

An endoparasite survey of a small pride of African lions (Panthera leo) was conducted at Intu Afrika Kalahari Game Reserve, southwestern Namibia, during winter and summer of 2003 and 2004, respectively. Overall, 23 fresh lion scats were collected opportunistically during fieldwork trials. A flotation technique was employed for the diagnosis of parasites. Three nematodes, Ancylostoma braziliense, Gnathostoma spinigerum and Uncinaria stenocephala and two coccidians, Toxoplasma gondii and Isospora felis were recorded. By using the McMaster method for quantification, a maximum number of 14 866 oocysts per gram of faeces was obtained for I. felis during winter 2003. Endoparasite taxa carried by the different individuals in the pride were found to be related to their levels of association. Rates of infection were relatively low as a result of the habitat, semi-captive conditions and earlier sporadic deworming

Feeding association between cattle egrets (<i>Bubulcus ibis<i/>) and mammal hosts in the central Free State

Field observations undertaken during October 1995 to April 2001 in agricultural areas and nature reserves of the central Free State, indicate that cattle egrets mainly feed in commensalistic association with ungulates or even farm implements. A higher percentage farm animals than game was involved herewith. Based on calculated preference indices only three species, namely cattle, buffalo and white rhino, qualified as key hosts. Eland, gemsbok, impala and horses were classified as major hosts, while the rest of the thirteen observed host species were identified as minor hosts. More than half of all feeding associations (58,4%) occurred during the early mornings followed by a decrease during the middle of the day with a slight increase again later in the afternoon. Depending on the host species involved, notable differences occurred in the time of association. Cattle were the only host species with which cattle egrets associated during any time of the day. Evidently, cattle egrets associated most often with larger host species which were actively grazing. In grassland habitats the birds mainly fed in front of grazing hosts, but behind those that moved too fast

Additions to the bird list of the Golden Gate Highlands National Park

Additions to the bird list of the Golden Gate Highlands National Par