Browsing by Author "Maphisa, David H"

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    The decline of the globally threatened Rudd's Lark in one of its last remaining core sites, the Wakkerstroom grasslands
    (2017) Gush, Wesley Gurney; Spottiswoode, Claire; Maphisa, David H; Donald, Paul
    Abstract The Rudd's Lark Heteromirafra ruddi is a globally threatened species with a fragmented population occurring in one of the world's most poorly-protected biomes, the grasslands. This, together with its endemism to the Highveld of South Africa and climate envelope modelling which predicts a dramatic reduction in its available habitat, places the species firmly in the cross-hairs of extinction risk. This thesis aims to gain a better understanding of Rudd's Lark population trends, habitat preference and threats in one of its most important remaining core sites in the grasslands around Wakkerstroom, Mpumalanga Province, which are under private ownership and used predominantly for grazing. My objectives were, first, to determine whether the species has declined in the Wakkerstroom area since a survey conducted in 2002 by David Maphisa. Second, to determine what habitat variables predict Rudd's Lark incidence, whether there has been a change in its available habitat and in farm management practices, and whether the species has changed in its habitat selection since the previous survey. Finally, I aimed to investigate whether other grassland birds (particularly other threatened grassland endemics) also respond to fine-scale habitat variation and share habitat preference with the Rudd's Lark. I found both absolute lower numbers of Rudd's Larks (5 transects with Rudd's Lark present down from 9 in 2002; 9 individuals down from 32), and a lower probability of encounter (significantly lower in the case of individuals). Seven transects had been lost to crop production, two of which formerly contained Rudd's Larks. Forb and dead vegetation cover had significantly increased at a coarse scale, but vegetation variables did not explain any significant variation in Rudd's Lark incidence at either a fine or a coarse scale within 2016. However, Rudd's Larks appear to be occupying subtly different habitat now compared to 12 years ago: lark territories surveyed in 2016 had less bare ground and more but shorter grass cover than in 2002. Most farmers reported warmer conditions in recent years and that burning generally took place between August and October, matching the analysis of remotely-sensed fire data from the past ten years and implying that destructive late-season fires are not common. Correspondingly, I found that burning regimes did not predict Rudd's Lark incidence. Among other threatened grassland species, Yellow-breasted Pipits showed a clear preference for taller grass and higher altitudes, unlike Rudd's Larks which showed no detectable preferences. In summary, direct loss of grassland habitat through conversion to crops appears to be a pressing threat to Rudd's Larks, although the species has also declined within the remaining area of grassland habitat. The specific drivers of this decline remain unclear given that the observed changes in grassland structure since 2002 do not correspond with Rudd's Lark habitat selection. Taken together, these findings are very concerning given that the Wakkerstroom area is considered to be one of the last remaining core sites for the species, and call its IUCN threat status of globally Vulnerable into question. A priority for future research will be to understand what limits Rudd's Larks to its current pockets of occupancy within its remaining apparently suitable grassland habitat, and whether increasing grassland fragmentation will accelerate its decline. Key words: fire, grassland, habitat selection, Heteromirafra ruddi, IUCN status, rangelands, Rudd's Lark, threatened species, transects
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    Drivers of bird species richness within moist high-altitude grasslands in eastern South Africa
    (Public Library of Science, 2016) Maphisa, David H; Smit-Robinson, Hanneline; Underhill, Les G; Altwegg, Res
    Moist high-altitude grasslands in South Africa are renowned for high avifaunal diversity and are priority areas for conservation. Conservation management of these areas conflicts with management for other uses, such as intensive livestock agriculture, which requires annual burning and leads to heavy grazing. Recently the area has become target for water storage schemes and renewable electricity energy projects. There is therefore an urgent need to investigate environmental factors and habitat factors that affect bird species richness in order to optimise management of those areas set aside for conservation. A particularly good opportunity to study these issues arose at Ingula in the eastern South African high-altitude grasslands. An area that had been subject to intense grazing was bought by the national power utility that constructed a pumped storage scheme on part of the land and set aside the rest for bird conservation. Since the new management took over in 2005 the area has been mostly annually burned with relatively little grazing. The new management seeks scientific advice on how to maintain avian species richness of the study area. We collected bird occurrence and vegetation data along random transects between 2006 and 2010 to monitor the impact of the new management, and to study the effect of the habitat changes on bird species richness. To achieve these, we convert bird transect data to presence only data to investigate how bird species richness were related to key transect vegetation attributes under this new grassland management. First we used generalised linear mixed models, to examine changes in vegetation grass height and cover and between burned and unburned habitats. Secondly, we examined how total bird species richness varied across seasons and years. And finally we investigated which habitat vegetation attributes were correlated with species richness of a group of grassland depended bird species only. Transects that were burned showed a larger decrease in vegetation cover compared to transects that were not burned. Grass height increased over time. Bird species richness was highest in summer compared to other seasons and increased over time. Overall bird species richness increased over the three summer surveys but species richness of birds that prefer heavily grazed habitat showed little change over the three years. Changes in bird species richness were best explained by the model with grass height for combined species richness of grassland depended birds but also for birds that prefer heavy grazing when treated alone. On one hand birds that prefer moderate grazing were best explained by a null model. However, overall bird species richness was better positively correlated to grass height than grass cover or dead grass. We conclude that frequent burning alone with relatively reduced grazing led to higher but less dense grass, which benefited some species and disadvantaged others. We suggest that management of this grassland use combination of fire and grazing and leave some areas unburned to accommodates birds of various habitat needs.