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Search Results: 1 - 10 of 118328 matches for " Colleen T. Downs "
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Abundance of the endangered Cape parrot, Poicephalus robustus in South Africa: implications for its survival
Colleen T. Downs
African Zoology , 2011,
Abstract: Factors affecting the decline of the endangered Cape parrot, which is endemic to South Africa, are presented. Its abundance and status were investigated during annual intensive national surveys. The merits of such a census are reported. Presence of birds was unpredictable at forest patches throughout its range. Present distributions in forest fragments reflect past distribution in a larger mosaic of forest patches. Numbers are low and the best estimate of numbers is 300–350 birds in the Eastern Cape, 170–220 in KwaZulu-Natal, and 50–60 in Limpopo Province. This suggests less than 1000 Cape parrots remain in the wild. About 20% of the entire population of the Cape parrot resident within the forest mosaic of southern KwaZulu-Natal roosts in one particular forest, which consequently needs urgent conservation protection.
Abundance and home ranges of feral cats in an urban conservancy where there is supplemental feeding: a case study from South Africa
Jaclyn Tennent,Colleen T. Downs
African Zoology , 2011,
Abstract: There is much debate surrounding the impact of feral cats (Felis catus) on wildlife. Conservancies are usually areas where indigenous flora and fauna are protected and aliens excluded or managed. The University of KwaZulu-Natal’s Howard College campus (HCC) is an urban conservancy containing feral cats that are presently not managed, and little is known about their ecology and behaviour. Consequently a feral cat population census was conducted, and their home range investigated. Estimates of the overall campus feral cat population numbers ranged between 23.4–40.0 cats/km2 with a minimum of 55 identified as resident. They were not randomly distributed in the study area, with spacing patterns being related to resource availability. Home range area and core distribution of eight radio-collared cats were determined over 13 months. Total home range areas were relatively small, with considerable overlap between them. Home ranges were clustered in areas with permanent feeding stations and these were also within the cats’ core ranges. Supp
Characterizing the thermal environment of small mammals: what should we be measuring, and how?
Joy C Coleman, Colleen T Downs
Open Access Animal Physiology , 2010, DOI: http://dx.doi.org/10.2147/OAAP.S13270
Abstract: racterizing the thermal environment of small mammals: what should we be measuring, and how? Methodology (4052) Total Article Views Authors: Joy C Coleman, Colleen T Downs Published Date September 2010 Volume 2010:2 Pages 47 - 59 DOI: http://dx.doi.org/10.2147/OAAP.S13270 Joy C Coleman, Colleen T Downs School of Biological and Conservation Sciences, Scottsville, Pietermaritzburg, South Africa Abstract: Operative temperature and standard operative temperature have been proposed as providing an estimate of the thermal load experienced by endotherms and ectotherms. Common techniques of measuring operative temperature include black-bulb temperatures or simplified unheated metal models, typically made of copper. We quantified the thermal environment perceived by a small, arboreal rodent using a number of methods at three study sites in winter and summer. Our area of interest was how well these methods accurately portrayed the actual temperatures that small mammals are exposed to. We predicted that black-bulb and copper model temperatures would more accurately predict operative temperature during photophase when compared with other direct measurements/devices, and that black-bulb temperature would record the greatest variation in temperatures. Temperature differences between the methods were largest during the midday, when temperatures were highest. All methods recorded a greater range of temperatures during photophase than during scotophase. Black-bulb and model temperatures produced more accurate, rapid measurements when compared with measurements produced by direct temperature recording devices, particularly during photophase, when solar radiation is the major influence of heating. Other methods lagged behind black-bulb measurements. Although mean temperatures of some of the methods were significantly different, there was a high degree of correlation between all methods, even after randomization and generation of 25% and 10% subsamples. In studies requiring accurate time series measurements, it is suggested that black-bulb or copper models be employed rather than direct temperature recording devices. Simpler measurement devices would suffice for studies requiring an estimate of the temperature variation and trends in the microclimate of small mammals, particularly arboreal or cavity dwelling species.
Basking behaviour in the rock hyrax (Procavia capensis) during winter
Kelly J. Brown,Colleen T. Downs
African Zoology , 2011,
Abstract: Basking is a behaviour frequently observed in the rock hyrax (Procavia capensis) during winter that supposedly plays a significant role in rewarming from nocturnal hypothermia. This behaviour, together with changes in body temperature and changes in black bulb temperatures(T bb) were investigated in the natural environment. In this study, rock hyraxes did not reduce their body temperature substantially overnight and thus basking was not used for rewarming but rather to maintain constant body temperatures under low ambient conditions. Frequency of basking changed throughout the day as T bb increased and decreased. Different basking postures (hunched or flat), orientations to the sun and basking bout lengths were modified depending on T bb experienced. There was no difference in body temperature between the two basking postures at any T bb. It appears that rock hyraxes did not use basking behaviour as a way of warming up after night-time but used it during the day as a diurnal energy conserving me
The status of habitat of great white and pink-backed pelicans in northeastern KwaZulu-Natal, South Africa: a review
Meyrick B. Bowker,Colleen T. Downs
African Zoology , 2011,
Abstract: Habitat change, mainly through the actions of humans, poses a threat to great white (Pelecanus onocrotalus) and pink-backed (P. rufescens) pelicans in northeastern KwaZulu-Natal, the southernmost distributions of these species on Africa’s eastern seaboard. This study assessed the relative importance and state of the potential pelican habitat in the northeastern KwaZulu-Natal region, focusing particularly on Lake St Lucia and the Phongolo River floodplain. Great white pelicans breed on islands in Lake St Lucia. Should these islands be lost through falling water levels or their becoming joined to mainland by deposits of silt, or by flooding, no suitable habitat for their breeding will remain in the region. By contrast, the pink-backed pelican nests in trees, and there appears to be plentiful alternative habitat. Lake St Lucia and, to a lesser extent, the Phongolo River floodplain, are important foraging areas for both pelican species. The hydrology of both these systems has been affected by human activities.
Habitat Characteristics of Forest Fragments Determine Specialisation of Plant-Frugivore Networks in a Mosaic Forest Landscape
Lackson Chama, Dana G. Berens, Colleen T. Downs, Nina Farwig
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0054956
Abstract: Plant-frugivore networks play a key role in the regeneration of sub-tropical forest ecosystems. However, information about the impact of habitat characteristics on plant-frugivore networks in fragmented forests is scarce. We investigated the importance of fruit abundance, fruiting plant species richness and canopy cover within habitat fragments for the structure and robustness of plant-frugivore networks in a mosaic forest landscape of South Africa. In total, 53 avian species were involved in fruit removal of 31 fleshy-fruiting plant species. Species specialisation was always higher for plants than for frugivores. Both species and network-level specialisation increased with increasing fruit abundance and decreased with increasing fruiting plant species richness and canopy cover within fragments. Interaction diversity was unaffected by fruit abundance and canopy cover, but increased slightly with increasing fruiting plant species richness. These findings suggest that especially the availability of resources is an important determinant of the structure of plant-frugivore networks in a fragmented forest landscape.
Abundance and activity patterns of the Cape parrot (Poicephalus robustus) in two afromontane forests in South Africa
J.O. Wirminghaus,Colleen T. Downs,M.R. Perrin,C.T. Symes
African Zoology , 2011,
Abstract: Behaviour, movements and numbers of the rare Cape parrot (Poicephalus robustus) were investigated at two study sites to assess its conservation status and as the basis for an action plan for their conservation. Birds flew regularly to and from nearby forests and were observed arriving at a feeding site (Hlabeni) from roosting sites in the morning. Numbers varied monthly and seasonally between the sites. Mean monthly (±SE) number of birds observed daily was 21.8 ±2.5 (n = 45) but ranged from 0–80. Activity was bimodal: it commenced at sunrise, lasted several hours, and was followed by inactivity through mid-day; activity recommenced a few hours before sunset and continued until sunset. Activity reflected changing day length. Causes of localized movements included food and water availability, and in summer some birds fed in fruit orchards. The relevance of counts of Cape parrots for the conservation of this species is reviewed.
Species Composition, Distribution and Habitat Types of Odonata in the iSimangaliso Wetland Park, KwaZulu-Natal, South Africa and the Associated Conservation Implications
Lorinda A. Hart, Meyrick B. Bowker, Warwick Tarboton, Colleen T. Downs
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0092588
Abstract: Maputaland–Pondoland–Albany, South Africa has been identified as a biodiversity hotspot and centre for endemism. Odonata make good indicators of freshwater ecosystem health. Consequently we compiled a list of Odonata species recorded to date in the iSimangaliso Wetland Park. We then detailed important species in terms of endemism, conservation status, and potential as indicator species. Finally, we compared Odonata assemblages of different sites sampled within the park to illustrate habitat importance. Species identified during two formal surveys and incidental observations made during the study period were combined with an existing database to compile an accurate and up to date species list for the iSimangaliso Wetland Park. Data from this study were then analyzed to determine which water bodies had the most similar species composition. The Dragonfly Biotic Index (DBI) value of each study area was also determined. We recorded 68 odonate species in the iSimangaliso Wetland Park, adding 13 species to the Ezemvelo KwaZulu-Natal Wildlife database for the area. This brings the total number of Odonata species for the iSimangaliso Wetland Park to 86. Eight species are red-listed, 12 are restricted in South Africa to the coastal plains of northern KwaZulu-Natal, and the remainder occurs widely across the southern African savanna. Analyses indicate that species odonate assemblages were most similar in water bodies with comparable habitats. iSimangaliso Wetland Park is identified as an important area for Odonata diversity and endemism, a trend also reflected by the DBI values. Shifts in the existing species assemblages would indicate changes within the ecosystem and thus this species account provides necessary baseline data for the area. Species Conservation efforts should thus target water bodies of varying habitat types to protect greater species diversity.
Cauchy Families of Directional Distributions Closed Under Location and Scale Transformations
T.D. Downs
The Open Statistics & Probability Journal , 2009, DOI: 10.2174/1876527000901010076]
Abstract: Directional statistics deals with angular data that come from non-linear objects such as circle circumferences or toroidal surfaces. A fundamental problem in directional statistics is that arithmetic cannot be meaningfully done on angles. Naive changes of location and scale like λ' = (λ – μ)/s for a spherical longitude λ are inappropriate and often misleading since they are not interpretable as one-one mappings from a sphere onto itself. Finding ways to obtain angular scale changes and to construct families of spherical probability distributions that are closed under such scale changes have been unsuccessful. But, such families are successfully constructed herein by indirect but historically powerful methods. Thus, a unit sphere with a uniform probability distribution on its surface is centrally rotated to a suitable position, and then stereographically projected onto an extended complex plane, a linear surface especially amenable to directional and statistical computations. A central dilation is performed on the plane, the dilated plane is projected back in effect as a rescaled sphere, and the rescaled sphere is again rotated. This process induces a family of spherical Cauchy-type probability distributions on the sphere that is closed under composition of such processes (rotate sphere, project sphere to plane, dilate plane, project dilated plane back as a rescaled sphere, and rotate again). The distributions so induced can be generalized to higher dimensional spheres that are also closed under location and scale transformations. These distributions enjoy numerous interrelationships with one another and with linear and circular Cauchy distributions.
Schaurteite, Ca3Ge(SO4)2(OH)6·3H2O
Marcus J. Origlieri,Robert T. Downs
Acta Crystallographica Section E , 2013, DOI: 10.1107/s1600536812050945
Abstract: This report presents the first crystal structure determination of the mineral schaurteite, ideally Ca3Ge(SO4)2(OH)6·3H2O, tricalcium germanium bis(sulfate) hexahydroxide trihydrate. This single-crystal X-ray diffraction study investigated a natural sample from the type locality at Tsumeb, Namibia. Schaurteite is a member of the fleischerite group of minerals, which also includes fleischerite, despujolsite, and mallestigite. The structure of schaurteite consists of slabs of Ca(O,OH,H2O)8 polyhedra (site symmetry mm2) interleaved with a mixed layer of Ge(OH)6 octahedra (-3m.) and SO4 tetrahedra (3m.). There are two H atoms in the asymmetric unit, both located by full-matrix refinement, and both forming O—H...O hydrogen bonds.
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