Distribution and habitat preference of redbacked shrikes lanius collurio in southern africa
TL;DR: Bruderer et al. as mentioned in this paper studied the distribution and habitat preference of Redbacked Shrikes Lanius collurio in southern Africa, and reported rates of redbacked shrikes provided by th...
Abstract: Bruderer B. & Bruderer H. 1993. Distribution and habitat preference of Redbacked Shrikes Lanius collurio in southern Africa. Ostrich 64: 141–147. Reporting rates of Redbacked Shrikes provided by th...
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TL;DR: To determine whether patterns of avian species turnover reflect either biome or climate transitions at a regional scale, and whether anthropogenic landscape transformation affects those patterns, a large-scale study of bird species turnover is proposed.
Abstract: Aim To determine whether patterns of avian species turnover reflect either biome or climate transitions at a regional scale, and whether anthropogenic landscape transformation affects those patterns.
Location South Africa and Lesotho.
Methods Biome and land transformation data were used to identify sets of transition areas, and avian species occurrence data were used to measure species turnover rates (β-diversity). Spatial congruence between areas of biome transition, areas of high vegetation heterogeneity, high climatic heterogeneity, and high β-diversity was assessed using random draw techniques. Spatial overlap in anthropogenically transformed areas, areas of high climatic heterogeneity and high β-diversity areas was also assessed.
Results Biome transition areas had greater vegetation heterogeneity, climatic heterogeneity, and β-diversity than expected by chance. For the land transformation transition areas, this was only true for land transformation heterogeneity values and for one of the β-diversity measures. Avian presence/absence data clearly separated the biome types but not the land transformation types.
Main conclusions Biome edges have elevated climatic and vegetation heterogeneity. More importantly, elevated β-diversity in the avifauna is clearly reflected in the heterogeneous biome transition areas. Thus, there is spatial congruence in biome transition areas (identified on vegetation and climatic grounds) and avian turnover patterns. However, there is no congruence between avian turnover and land transformation transition areas. This suggests that biogeographical patterns can be recovered using modern data despite landscape transformation.
45 citations
Cites background from "Distribution and habitat preference..."
...Furthermore, whilst it is well known that the avifauna responds to local vegetation heterogeneity in southern Africa (Hockey et al., 1988; Bruderer & Bruderer, 1993), and in other regions (Cody, 1985, 1993; Gentilli, 1992; Blondel & Vigne, 1993; MacNally, 1997; Wiebe & Martin, 1998), Allan et al.…...
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TL;DR: Red-backed shrikes’ population dynamics are driven by environmental factors operating at various scales of space and time, but only a small amount of the temporal variation in demographic rates is explained by the environmental factors considered, suggesting that additional factors, such as those operating during migration, might be important.
Abstract: Demographic rates of migratory species passing through several areas during their annual cycle may be affected by environmental conditions at each of these areas. Recent studies provide evidence that their impact is not necessarily immediate, but can be delayed. We studied survival, reproductive success and arrival date at the breeding grounds of red-backed shrikes Lanius collurio, a trans-Saharan migrant, in relation to weather and vegetation on the breeding grounds, the stopover sites during migration and in the wintering areas. These environmental factors are used as proxy of the shrike’s food supply. We analysed detailed demographic data of some 4,600 individuals from 25 years with multistate capture–recapture and mixed models. Survival probabilities of juveniles and breeders of both sexes varied in parallel across time, suggesting that all cohorts were sensitive to similar causes of mortality. Reproductive performance increased with temperature and decreased with rainfall on the breeding area. Moreover, it increased with vegetation cover in the Sahelian stopover area used on autumn migration suggesting a carry-over effect. Arrival date was negatively affected by spring temperatures in the breeding area. Hence, demographic rates were affected by environmental factors on the breeding grounds, but also outside and elsewhere. This suggests that the shrike’s population dynamics are driven by environmental factors operating at various scales of space and time. However, only a small amount of the temporal variation in demographic rates is explained by the environmental factors considered, suggesting that additional factors, such as those operating during migration, might be important.
41 citations
Cites background from "Distribution and habitat preference..."
...The main non-breeding habitats are arid savannahs (Bruderer and Bruderer 1993, 1994; Jakober et al. 2007)....
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TL;DR: This article examined biogeographical affiliations, habitat-associated heterogeneity and endemism of avian assemblages in sand forest patches and the savanna-like mixed woodland matrix.
Abstract: Aim To examine biogeographical affiliations, habitat-associated heterogeneity and endemism of avian assemblages in sand forest patches and the savanna-like mixed woodland matrix.
Location Two reserves in the Maputaland Centre of Endemism (MC) on the southern Mozambique Coastal Plain of northern KwaZulu-Natal, South Africa.
Methods Replicated surveys were undertaken in each of the two habitat types in each reserve, providing species abundance data over a full year. Vegetation structure at each of the survey sites was also quantified. Differences between the bird assemblages and the extent to which vegetation structure explained these differences were assessed using multi-variate techniques. Biogeographical comparisons were based on species presence/absence data and clustering techniques.
Results Bird assemblages differed significantly between habitats both within a given reserve and between reserves, and also between reserves for a given habitat. Differences in vegetation structure contributed substantially to differences between the avian assemblages. Of the four species endemic to the MC, three (Neergaard’s sunbird, Rudd’s apalis, and Woodward’s batis) were consistently present in sand forest. The fourth (pink-throated twinspot) preferred mixed woodland. None of these endemic species was classed as rare. In the biogeographical analysis, both the sand forest and the mixed woodland bird assemblages were most similar to bird assemblages found in the forest biome or the Afromontane forest biome, depending on the biome classification used.
Main conclusions The close affinities of sand forest and mixed woodland assemblages to those of the forest biome are most likely due to similarities in vegetation structure of these forests. Bird assemblages differ between the sand forest and mixed woodland habitats both within a given reserve and between reserves, and also between reserves for a given habitat. These differences extend to species endemic to the MC. Thus, conservation of sand forest habitat in a variety of areas is necessary to ensure the long-term persistence of the biota.
32 citations
TL;DR: In this paper, a quantitative, systematic analysis of the different bird communities spanning the Karoo was undertaken to examine contributions of broad and local-scale physical environmental and biotic factors to regional variations in the species composition, using multivariate statistical and spatial analytical tools.
Abstract: Aim To identify and quantify biotic and abiotic factors associated with the regional gradients in the distribution and abundance of bird communities restricted and endemic to the Succulent and Nama Karoo biomes of South Africa. Location The arid Nama and Succulent Karoo biomes in South Africa. Methods The quarter degree grid cell (QDGC) was used to extract environmental data, while the bird data previously atlased, was linked to the same geo-referenced system, using a geographical information system (GIS). Bird species were grouped into different life-history assemblages. A quantitative, systematic analysis of the different bird communities spanning the Karoo was undertaken to examine contributions of broad- and local-scale physical environmental and biotic factors to regional variations in the species composition, using multivariate statistical and spatial analytical tools. These included two indirect gradient methods; principal components analysis (PCA) and detrended correspondence analysis (DCA), and two direct gradient methods; canonical correspondence analysis (CCA) and redundancy analysis (RDA). Results Principal components analysis results showed that the selected environmental variables accounted for about 85% of the variation in the region. The first two principal gradients defined regional temperature seasonality and variability especially in winter and summer. The third principal gradient mainly defined summer rainfall areas in association with the coefficient of variation of rain and regional primary production, while the fourth gradient defined winter rainfall areas, growth days and elements of landscape structure. CCA ⁄ RDA analysis produced shortened hierarchically ranked explanatory variables for each bird assemblage. Stepwise gradient analysis results showed summer rain, rainfall concentration, topographic heterogeneity and annual evapotranspiration, as the most important climate variables explaining species occurrence. Landscape, in terms of percentage transformation, morphology, coefficient of variation of primary productivity and distance between suitable habitat patches, were also important, but to a lesser degree. Total variation explained (TVE) by the supplied variables was between 23 and 37% of variation. Less than 20% of TVE was the intrinsic spatial component of environmental influence, indicating that any unmeasured factors were independent of spatial structuring. For all the eight bird assemblages, climate contributed most to TVE (24‐57%). Landscape characteristics (human-induced transformation, vegetation in terms of size if grassy clumps and the average distances between them) contributed the least to TVE for all the different assemblages (0‐6%), especially the granivorous assemblage where it was not significant at all (0%). Seasonal extremes and variability were more important in explaining species gradients than were annual climatic conditions, with the exception of annual potential evapotranspiration.
26 citations
Cites result from "Distribution and habitat preference..."
...It is noteworthy that unlike other studies (e.g. Bruderer & Bruderer, 1993; Dean, 2000), none of the geological variables were identified as significant by the stepwise CCA....
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TL;DR: The sex differences in habitat occupation on the non-breeding grounds in the Red-backed Shrike are the first such differences documented in any PalaearcticAfrican migrant passerine.
Abstract: Lesser Grey Shrikes and Red-backed Shrikes have much smaller ranges on the non-breeding grounds in the Kalahari basin than during breeding. This study investigated whether, as a result of competition, habitat segregation occurs on the non-breeding grounds. Migrant shrikes were surveyed in point-transect counts in 19 vegetation types in Botswana. There were clear differences in habitat distribution between the species, and also between the sexes in the Red-backed Shrike. Female Red-backed Shrikes occupied more densely wooded bushveld than males, while Lesser Grey Shrikes occupied the most open habitat and overlapped more frequently with male than with female Red-backed Shrikes. More subtle differences along gradients of herbaceous ground cover suggest that differences in habitat quality may be involved, the dominant species (Lesser Grey Shrike) occupying, on average, the best and the most subordinate birds (female Red-backed Shrikes) the poorest habitat. The sex differences in habitat occupation on the non-breeding grounds in the Red-backed Shrike are the first such differences documented in any PalaearcticAfrican migrant passerine.
22 citations
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1,893 citations
01 Jan 1982
TL;DR: The term "savanna" has become synonymous with African plainslands - grasslands studded with flat-crowned acacias and carrying a profusion of wild ungulates as mentioned in this paper.
Abstract: In recent years the term “savanna” has become synonymous with African plainslands - grasslands studded with flat-crowned acacias and carrying a profusion of wild ungulates. In this chapter the term will be used in a wider context, to include all ecosystems in which C4 grasses potentially dominate the herbaceous stratum and where woody plants, usually fire-tolerant, vary in density from widely scattered individuals to a closed woodland broken now and again by drainage-line grasslands. Rainfall occurs in the warmer, summer months with a dry period of between two to eight months duration during which fire is a typical phenomenon at intervals varying from one to fifty years.
200 citations