The distribution and biology of nomadic birds in the Karoo, South Africa

Dryland nomadic bird species, as a proportion of all bird species in a biome in southern Africa, are highest in the arid grassland and arid and semi-arid Karoo in South Africa. Nomadic birds, of which the most widespread species is the greybacked finchlark Eremopterix verticalis (Smith), are most frequently observed in the north-central and north western Nama Karoo. The species richness of nomadic species is inversely correlated with species richness of all bird species in the Karoo. Since the distribution of nomadic birds is in areas where rainfall is patchy, low (<250 mm per year) and aseasonal, this supports the idea that fewer species are able to cope with resources that are patchy in time and space, and that there has been selection for nomadism in the species that are able to use patchy environments. Species richness and abundance of nomadic birds is negatively correlated with rainfall amount but positively correlated with the coefficient of variation of the rainfall and with rainfall in autumn. The frequency of nomadic birds is inversely correlated with altitude range; nomadic species are most often recorded in structurally simple habitats (shrubland and grassland) on open plains. Most nomadic bird species in the Karoo are granivorous. Perennial desert grasses are important components of the habitat and diet of small nomadic granivores, and also provide nest sites and nest material. Nomadic birds can breed throughout the year, without a clearly defined ‘season’ in both the Succulent and Nama Karoo. Average clutch sizes do not differ significantly between resident and all nomadic species in the arid and semi-arid Karoo. Nomadism is an evolutionary stable strategy for individual species only when extremes in environmental conditions are frequent enough, and unpredictable enough, to maintain movements to high resource patches or to maintain dispersal away from low resource patches. If high rainfall years are too regular or infrequent, or peaks in fluctuations of resources in the environment too low, or rainfall patches are randomly distributed, nomadism would not be maintained as part of the individual behaviour pattern.     

The Orange River avifauna: abundance,richness and comparisons

Like many other southern African rivers, the avifaunal richness and abundance of the Orange River, southern Africa's longest, remains virtually unknown. Given that the Orange River runs through hyper-arid regions in its lower reaches, its linear oasis effect and its role as a reservoir for Red Data bird species is likely but has not been quantified. Two surveys either side of the border town of Noordoewer, in the rainy and dry seasons of 1996 and 1997 deter-mined that species richness was higher in riverine habitat (71 species) than in the surrounding Nama Karoo (46 species) confirming the linear oasis effect. Surveys revealed five Namibian Red Data species. Peregrine Falcons, Falco peregrinus, and African Fish Eagles, Haliaeetus vocifer, were relatively common while the endangered Cape Eagle Owl, Bubo capensis, occurred sporadically. Among wetland Red Data bird species, Black Storks, Ciconia nigra, occurred in less disturbed areas, and White-backed Night Herons, Gorsachius leuconotus, were an unexpected species at this locality. The overall species richness of 103 birds and a density of riparian birds of 31 -3 4 birds/10 km, makes the lower Orange River avifauna similar to the Cunene River but tenfold less abundant than Namibia's other perennial rivers. Despite the low diversity, the arid habitats of the lower Orange River support greater diversity than more easterly regions when all current surveys of richness and abundance from Lesotho to the mouth on the Namib coast are combined. This east-west trend may be explained by the slower flow and warmer water of the lower Orange River but natural turbidity and regulation may explain the generally low diversity and abundance indices. Major rivers in southern Africa appear to have been over-looked as wetland habitats, and further avifaunal surveys of all of them are recommended.     

Searching for potential wintering and migration areas of a Danish Barn Swallow population in South Africa by correlating NDVI with survival estimates

On the basis of correlation analyses between annual Normalised Difference Vegetation Index (NDVI) values in Africa and the annual survival rate estimated for a breeding population of barn swallows Hirundo rustica from Denmark, we identified potential wintering and migration areas in South Africa during December–February and March–May, when barn swallows commonly occur in South Africa. During December–February we identified potential wintering areas only in the western part of South Africa, in the Karoo. Potential areas in the central and eastern parts of the country were only identified during March–May. NDVI values in the Karoo during March–May explained most of the variance in annual adult survival rate of the population. The high ratio of European ringed barn swallows among controlled individuals in the Karoo was similar to the ratio that would be expected based on the number of ringed barn swallows and the population sizes of barn swallows in north-western European breeding populations. The level of this ratio in the Karoo was higher than in any other locality in the central and eastern parts of South Africa and Botswana, indicating that ringed birds from the eastern flyway are absent to a much smaller extent than ringed birds from the western flyway. This approach shows that the NDVI and survival method can focus ringing efforts to regions and areas that are likely to harbour specific breeding populations, thereby helping to identify potential wintering and migration areas for breeding populations of migratory birds.     

Stable isotopes reveal regional movement patterns in an endangered bustard

Stable isotope analysis is a valuable technique to infer animal movement between isotopically distinct landscapes. For birds in terrestrial systems, it is usually only applied at continental scales, often relying on global isotopic patterns. In contrast, we used this technique to investigate movement patterns of Ludwig's bustard (Neotis ludwigii) at a regional scale, where such information is needed to improve the conservation status of this species. We analysed carbon and nitrogen isotopic compositions of feathers from bustards across two biomes of the semi‐arid rangelands of the Karoo, South Africa, to investigate movement and explore sex and age movement strategy differences. We used a linear discriminant function analysis based on growing feathers to classify fully grown feathers to a Succulent or Nama Karoo biome origin. Six of 12 birds for which all primary feathers were analysed had at least one feather classified as having grown in the Succulent Karoo, supporting the theory that these birds are partial migrants. Feathers from two satellite‐tracked bustards broadly supported the conclusions of the analysis, although food base differences resulting from local rainfall variation probably obscured geographic signals at finer scales. There was no apparent difference in movement strategies between the sexes, but juvenile feathers were almost exclusively assigned to the Nama Karoo, suggesting that most breeding occurs in this biome. Adult and juvenile feathers also had significantly different isotope ratios, which could relate to diet or to differing metabolic processes. This study demonstrates that with a good understanding of the system, carbon and nitrogen stable isotopes can be useful to infer general movement patterns of birds at a regional level.     

Large-Scale Range Collapse of Hawaiian Forest Birds under Climate Change and the Need 21st Century Conservation Options

Hawaiian forest birds serve as an ideal group to explore the extent of climate change impacts on at-risk species. Avian malaria constrains many remaining Hawaiian forest bird species to high elevations where temperatures are too cool for malaria’s life cycle and its principal mosquito vector. The impact of climate change on Hawaiian forest birds has been a recent focus of Hawaiian conservation biology, and has centered on the links between climate and avian malaria. To elucidate the differential impacts of projected climate shifts on species with known varying niches, disease resistance and tolerance, we use a comprehensive database of species sightings, regional climate projections and ensemble distribution models to project distribution shifts for all Hawaiian forest bird species. We illustrate that, under a likely scenario of continued disease-driven distribution limitation, all 10 species with highly reliable models (mostly narrow-ranged, single-island endemics) are expected to lose >50% of their range by 2100. Of those, three are expected to lose all range and three others are expected to lose >90% of their range. Projected range loss was smaller for several of the more widespread species; however improved data and models are necessary to refine future projections. Like other at-risk species, Hawaiian forest birds have specific habitat requirements that limit the possibility of range expansion for most species, as projected expansion is frequently in areas where forest habitat is presently not available (such as recent lava flows). Given the large projected range losses for all species, protecting high elevation forest alone is not an adequate long-term strategy for many species under climate change. We describe the types of additional conservation actions practitioners will likely need to consider, while providing results to help with such considerations.     

Neotropical bromeliads as food sources for birds: a systematic review and perspectives on the management of ecological interactions

The loss of interactions and ecosystem functions is a concerning by-product of pervasive Anthropocene species decline and extinction. Ecological interactions between species sustain the provision of ecosystem processes, especially those mediated by trophic relationships such as pollination and predation. At the local habitat scale, the diversity of natural food sources may increase the diversity of interactions, thus enhancing the stability of local communities and ecosystem functioning. Here I discuss the importance of bromeliads as a potential provider of additional trophic interactions with birds, a key animal group in the Neotropics. Based on 88 studies published between 1965 and 2020 across the Neotropical region, I observed that bromeliads act as ‘wildlife restaurants’ by providing an additional food source throughout the year in almost all Neotropical ecosystems for at least 162 bird species (mostly hummingbirds). These plants (both epiphytic and terrestrial forms) can provide nectar, flowers, water for drinking, invertebrates, small vertebrates, seeds, and fruits, as well as nest materials and substrates. Given these trophic relationships between bromeliads and birds, actions to restore the richness and abundance of these plants in changed habitats would potentially enhance the local diversity of birds. I discuss and recommend the use of bromeliad transplantations as a relevant conservation tool for birds and some implications for the maintenance of species and interaction diversity in natural and agricultural habitats.     

High power line collision mortality of threatened bustards at a regional scale in the Karoo,South Africa

Quantifying avian collisions with power lines at large spatial scales is difficult, but such mortality is of serious conservation concern for many bird species worldwide. To investigate effects on the Endangered Ludwig's Bustard Neotis ludwigii and two other bustard species, mortality surveys were conducted quarterly along high‐voltage transmission lines at five sites (total length 252 km) across the Karoo for 2 years and one low‐voltage distribution line site (95 km) for 1 year. Thirty bird species were found, with Ludwig's Bustards constituting 69% and other bustards a further 18% of carcasses (n = 679 birds). Significant explanatory variables of Ludwig's Bustard collisions were season (collisions more likely in winter), rainfall (less likely in drier areas) and year on transmission lines (highlighting variability between years). Season and proximity to roads were significant variables on distribution lines, with collisions more likely during winter and away from roads. Ludwig's Bustard collision rates (corrected for survey biases) were higher on transmission (1.12; 95% confidence interval (CI) 0.40–2.58 bustards/km/year) than on distribution lines (0.86; 95% CI 0.30–1.96), but these smaller lines are four times as extensive in South Africa and so probably kill more birds. Despite being much less abundant, Kori Bustards Ardeotis kori were the second most commonly recovered species, with collision rates of 0.10 (95% CI 0.05–0.19) on transmission lines in the Nama Karoo alone. Collision rates are highly variable but suggest mortality suffered by these two species is worryingly high. This adds to growing concern about the impacts of power lines on bustards globally, so given ongoing expansion to the power grid, collision mitigation measures should be implemented at all new power lines.     

Primary productivity and species richness: relationships among functional guilds, residency groups and vagility classes at multiple spatial scales

One of the major determinants of species richness is the amount of energy available, often measured as primary productivity. Heterogeneity of environmental variables has also been found to influence species richness. Predicting species distributions across landscapes and identifying areas that have high species richness, or vulnerable groups of species, is useful for land management. Remotely sensed data may help identify such areas, with the Normalized Difference Vegetation Index (NDVI) providing an estimate of primary productivity. We examined the relationship between maximum productivity (NDVI), heterogeneity of productivity, and species richness of birds and butterflies at multiple spatial scales. We also explored relationships between productivity, functional guilds and residency groups of birds, and vagility classes of butterflies. Positive linear relationships between maximum NDVI and number of functional guilds of birds were found at two spatial scales. We also found positive linear relationships between maximum NDVI and species richness of neotropical migrant birds at two scales. Heterogeneity of NDVI, by contrast, was negatively associated with number of functional guilds of birds and species richness of resident birds. Maximum NDVI was associated with species richness of all butterflies and of the most vagile butterflies. No association was found between heterogeneity of NDVI and species richness of butterflies. In the Great Basin, where high greenness and availability of water correspond to areas of high species richness and maximum NDVI, our results suggest that NDVI can provide a reliable basis for stratifying surveys of biodiversity, by highlighting areas of potentially high biodiversity across large areas. Measures of heterogeneity of NDVI appear to be less useful in explaining species richness.     

Risk‐taking and the evolution of mechanisms for rapid escape from predators

Flight initiation distance (FID) is the distance at which an individual animal takes flight when approached by a human. This behavioural measure of risk‐taking reflects the risk of being captured by real predators, and it correlates with a range of life history traits, as expected if flight distance optimizes risk of predation. Given that FID provides information on risk of predation, we should expect that physiological and morphological mechanisms that facilitate flight and escape predict interspecific variation in flight distance. Haematocrit is a measure of packed red blood cell volume and as such indicates the oxygen transport ability and hence the flight muscle contracting reaction of an individual. Therefore, we predicted that species with short flight distances, that allow close proximity between a potential prey individual and a predator, would have high haematocrit. Furthermore, we predicted that species with large wing areas and hence relatively low costs of flight and species with large aspect ratios and hence high manoeuvrability would have evolved long flight speed. Consistent with these predictions, we found in a sample of 63 species of birds that species with long flight distances for their body size had low levels of haematocrit and large wing areas and aspect ratios. These findings provide evidence consistent with the evolution of risk‐taking behaviour being underpinned by physiological and morphological mechanisms that facilitate escape from predators and add to our understanding of predator–prey coevolution.     

Rainfall as a breeding stimulus and clutch size determinant in South African arid-zone birds

Rainfall is known to be a stimulus for initiating breeding in arid-zone birds, but its influence on clutch size is unknown for most southern African birds. The breeding activity of nine out of 11 species studied in the arid Nama Karoo biome of South Africa increased markedly after appreciable rainfall. Some resident insectivores did breed in the absence of rainfall, even under drought conditions, but also laid eggs within one week of small rain showers. Nomadic granivores required more substantial rainfall to stimulate what was usually a synchronized, population-wide breeding response. The timing and length of the breeding season was dependent on the integrated effect that rainfall and temperature had on the growing season of the vegetation. Over 50% of the 11 species studied showed evidence of an increase in clutch size following large rainfall events. Grey-backed Finchlark Eremopterix verticalis began laying larger clutches within one week of a rainfall stimulus, illustrating how rapid this response can be.     

The dynamics of a succulent karoo vegetation

Strong inference techniques were used in a preliminary study of the structure and dynamics of the vegetation the Prince Albert region of the Great Karoo, South Africa. Seedling emergence studies indicate that open areas in the interstices of the existent vegetation are colonized by mound-building species of the Mesembryanthemaceae. Later, these species serve as sites of establishment for seedlings of several species of woody shrubs. Eventually, the woody shrubs replace the mound-building mesems through interspecific competition. The woody shrubs persist in the community until they reach senescence and die or are removed through overgrazing. Superimposed on this dynamic pattern is a further temporal pattern involving a combination of disturbance and subsequent soil changes. Much of this effect is caused by fossorial animals, which are associated with large circular (10–20 m diameter) mounds. Burrowing by these animals changes the soil characteristics and establishes an additional sequence of vegetation succession in which the mounds serve as refuges from which non-palatable species, such as Pteronia pallens, can invade the rangeland. Later, as the mounds are abandoned and disturbance effects cease, more palatable species, such as P. empetrifolia, will replace P. pallens, overcoming finally the effects of the adjacent mounds on the surrounding vegetation.     

High juvenile mortality during migration in a declining population of a long‐distance migratory raptor

Many populations of long‐distance migrants are declining and there is increasing evidence that declines may be caused by factors operating outside the breeding season. Among the four vulture species breeding in the western Palaearctic, the species showing the steepest population decline, the Egyptian Vulture Neophron percnopterus, is a long‐distance migrant wintering in Africa. However, the flyways and wintering areas of the species are only known for some populations, and without knowledge of where mortality occurs, effective conservation management is not possible. We tracked 19 juvenile Egyptian Vultures from the declining breeding population on the Balkan Peninsula between 2010 and 2014 to estimate survival and identify important migratory routes and wintering areas for this species. Mortality during the first autumn migration was high (monthly survival probability 0.75) but mortality during migration was exclusively associated with suboptimal navigation. All birds from western breeding areas and three birds from central and eastern breeding areas attempted to fly south over the Mediterranean Sea, but only one in 10 birds survived this route, probably due to stronger tailwind. All eight birds using the migratory route via Turkey and the Middle East successfully completed their first autumn migration. Of 14 individual and environmental variables examined to explain why juvenile birds did or did not successfully complete their first migration, the natal origin of the bird was the most influential. We speculate that in a declining population with fewer experienced adults, an increasing proportion of juvenile birds are forced to migrate without conspecific guidance, leading to high mortality as a consequence of following sub‐optimal migratory routes. Juvenile Egyptian Vultures wintered across a vast range of the Sahel and eastern Africa, and had large movement ranges with core use areas at intermediate elevations in savannah, cropland or desert. Two birds were shot in Africa, where several significant threats exist for vultures at continental scales. Given the broad distribution of the birds and threats, effective conservation in Africa will be challenging and will require long‐term investment. We recommend that in the short term, more efficient conservation could target narrow migration corridors in southern Turkey and the Middle East, and known congregation sites in African wintering areas.     

Evaluation of Restoration Techniques for the Succulent Karoo, South Africa

Abstract Possible constraints on the passive recovery of bare areas in the Karoo, a semiarid region in South Africa, include inadequate supply of seed, availability of suitable microsites for plant establishment, altered soil properties, and the truncation of key soil biotic processes. Here we investigate the possibility of initiating the restoration of bare areas by soil surface treatments with gypsum (CaSO₄) and/or organic mulch. We also apply an exogenous seed source to test the hypothesis that seed availability limits autogenic recovery. Both gypsum and mulch improved rain water infiltration, gypsum more so than mulch, and both treatments resulted in significantly higher numbers of reseeded seedlings compared with controls. Gypsum also improved the survival of the cohorts of seedlings of the larger seeded Tripteris sinuata. Tripteris showed the highest number of seedlings (maximum count of 150 seedlings/1,000 viable seeds sown) and surviving plants of the three reseeded species, which included two small‐seeded species, Ruschia spinosa and Chaetobromus dregeanus. Throughout the study period significantly higher plant volumes of naturally seeded annuals and perennials were recorded in the gypsum and/or mulch treatments compared with the controls. Germination and emergence of reseeded and naturally seeded plants appears to be determined by the availability of cool season (autumn to spring ) soil moisture, whereas follow‐up rainfall during this time is important for plant survival. Mulching of bare areas in the Succulent Karoo has the potential to re‐create vegetated areas that will further capture and conserve water, soil, and nutrients. Gypsum also showed positive results but might not be a cost‐effective option because of transport costs to these remote arid areas.     

Fruit size, crop mass, and plant height explain differential fruit choice of primates and birds

Seed dispersal by animals is an important ecological process shaping plant regeneration. In general, seed dispersers are highly variable and often opportunistic in their fruit choice. Despite much research, the factors that can explain patterns of fruit consumption among different animal groups remain contentious. Here, we analysed the interactions between 81 animal species feeding on the fruits of 30 plant species in Kakamega Forest, Kenya, during 840 h of observations. Our aim was to determine whether plant characteristics, fruit morphology, fruit colours and/or fruit compounds such as water, sugar, phenols and tannins explained the relative importance of fruit consumption by the two most important consumer groups, primates and birds. We found significant differences in fruit choice between both groups. Primates fed on larger fruits and on higher trees that had larger fruit crops, whereas birds were observed feeding on smaller fruits and on smaller plants producing fewer fruits. Fruit colours did not differ between fruits consumed by primates and those consumed by birds. However, differences in the fruit choice among frugivorous birds were associated with differences in fruit colours. Smaller plants with smaller fruits produced red fruits which contrasted strongly with the background; these fruits were dispersed by a distinct set of bird species. The contents of water, sugar, phenols and tannins did not differ between fruits eaten by primates and those eaten by birds. Some phylogenetic patterns were apparent; primates fed preferentially on a phylogenetically restricted subsample of large plants with large fruits of the subclass Rosidae. We discuss why the observed primate dispersal syndrome is most likely explained by a process of ecological fitting.     

Life form spectra in the Hantam-Tanqua-Roggeveld, South Africa

The Hantam-Tanqua-Roggeveld subregion is situated in an area where the Fynbos, Succulent Karoo and Nama Karoo biomes meet. Life form spectra were compiled at a species richness and vegetation cover level in order to determine the affinities of the vegetation of the subregion with respect to its Succulent Karoo, Fynbos and Nama Karoo Biome status. A percentage succulence was also calculated for both species richness and cover. Comparisons of life form spectra and succulence were made across the eight vegetation associations found in the area and across three broad vegetation groups, i.e., Mountain Renosterveld, Winter Rainfall Karoo and Tanqua Karoo. Mountain Renosterveld vegetation was characterised by high chamaephyte, cryptophyte and therophyte species contributions. Compared to the other broad vegetation groups, the Mountain Renosterveld group showed phanerophyte contributions at the vegetation cover level to be highest, but the degree of succulence was low. Winter Rainfall Karoo vegetation was co-dominated by high levels of chamaephyte, cryptophyte and therophyte species with chamaephytes dominating the vegetation cover. Succulent contributions to species richness and cover values were higher than for Mountain Renosterveld vegetation. Tanqua Karoo vegetation was dominated by chamaephyte species or co-dominated by chamaephyte and cryptophyte species with therophyte species contributions lowest of all vegetation groups. Contributions by succulent species to richness and vegetation cover were high in the Tanqua Karoo. Life form spectra of the Mountain Renosterveld associations compared poorly to other sites in the Fynbos Biome. However, the low level of succulence in the Mountain Renosterveld associations also precludes its inclusion into the Succulent Karoo Biome. The large contribution of succulent species at a species and vegetation cover level in Winter Rainfall Karoo and Tanqua Karoo associations confirms that these two groups belong to the Succulent Karoo Biome. Affinities to the Nama Karoo Biome were indicated by the low level of succulence at a vegetation cover level in one of the Winter Rainfall Karoo associations (Roggeveld Karoo).     

Endemism in Namibia: patterns, processes and predictions

Sandwiched between the Namib and Kalahari Deserts of southwestern Africa are the karooid and escarpment biotopes of Namibia which are rich in endemics of many taxa. Most plant, invertebrate, amphibian, reptile, mammal and bird species endemic to Namibia are found in a zone running through, and to the west of, Namibia's escarpment region. There is also an important region of endemism for succulent plants, reptiles and invertebrates in the Succulent Karoo biome. Congruence between endemism hotspots, particularly on rocky substrates, is remarkably high for most taxa, implying broadly similar speciation processes. Possible speciation mechanisms in different parts of the country include the spatial isolation of rupicolous taxa such as insects and reptiles by the formation of large coastal dune fields; the expansion and contraction of wooded savannas during pluvial and interpluvial periods; and global temperature shifts which created highland refugia for frost-susceptible plants and poikilotherms. Areas of endemism and species richness overlap poorly for Namibia's mainly arid-dwelling endemic vertebrates, as richness is highest in the mesic wetlands and woodlands of northeast Namibia. The overlap for succulent plants, insects and arachnids, however, is relatively high. Centres of endemism for plants and vertebrates fall mainly outside protected areas, as few parks were established with biodiversity indices in mind. Our analysis of endemism congruence provides a strong platform for the promulgation of new protected areas to safeguard Namibia's unique biota. Furthermore, analysis of speciation patterns and processes is a useful predictive tool for the identification of other biotically important sites.     

Plant and small mammal richness correlate positively in a biodiversity hotspot

Hotspots of biodiversity are important areas in facilitating an understanding of species richness and its maintenance. Herbivores can increase plant richness by reducing dominant plant species thus providing space for subdominant species. As small mammals are abundant in the Succulent Karoo and therefore might affect plant richness by means of herbivory, we tested if this mechanism might exist in the Succulent Karoo in southern Africa, a biodiversity hotspot due to its extraordinary plant richness. At ten ecologically different study sites we measured plant and small mammal richness and diversity and determined 11 abiotic factors including soil composition, altitude and rainfall. We found positive correlations between plant richness and the number of small mammal species. A general linear model revealed that the number of small mammal species was more important than abiotic factors in explaining variation in plant richness. To test whether small mammals might directly influence plant richness, we studied the influence of the bush-Karoo rat Otomys unisulcatus, a central place forager, on the plant community. The immediate surroundings of occupied O. unisulcatus nests showed significantly higher plant richness than control areas. We conclude that small mammals can have a positive effect on plant richness in the Succulent Karoo. While experimental data are needed to support these correlative results, the results of our study indicate that areas of high small mammal richness should be included in conservation programs of the Succulent Karoo.     

Hierarchical processes define spatial pattern of avian assemblages restricted and endemic to the arid Karoo, South Africa

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 theleast 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. Main conclusions This study was able to synthesize species environment relations at the broad scale and demonstrated the association of arid zone endemic species occurrence with climate extremes and seasonality. Given the predicted climate change scenarios for South Africa, this regional gradient study provides a quantitative ecological basis for finer scale modelling and analysis, developing regional strategies for conserving biodiversity as well as predicting and planning for the effects of global climate change. However, most importantly, it clearly showed that bird species restricted and endemic to the arid Karoo biome may be more sensitive to climate rather than vegetation structure as previously thought.     

Avian diversity in a Kenyan agroecosystem: effects of habitat structure and proximity to forest

Tropical agroecosystems cover an increasingly large proportion of the Earth’s terrestrial surface. Yet, relatively little is known about the factors that influence their avifauna, especially in areas of high human population density. The potential of tropical farmland for sustaining bird biodiversity, including forest birds, can be influenced by habitat structure and the distance from the nearest forest. We investigated the effect of these two factors on the bird community in the farmland near Kakamega Forest, Kenya. Using point counts, we assessed the number of bird species and individuals on 56 study plots in distances up to about 2,100 m from the forest. We observed a total of 96 bird species in the farmland, 22 of which were forest, 58 shrub-land, and 16 open-country species. High vertical vegetation heterogeneity and a large number of woody plant individuals were related to high species richness of forest and shrub-land birds, whereas open-country birds avoided such areas. The species richness and total number of forest birds declined with increasing distance to the forest. A comparison with the bird community within Kakamega Forest indicated that only a fraction of the forest species could be sustained in the farmland. This suggests that agroecosystems with a diverse habitat structure can support a high diversity of birds, but have only a limited capacity to compensate for forest loss. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Non-random distribution of ring recoveries from trans-Saharan migrants indicates species-specific stopover areas

Many long-distance migrant birds regularly have to pass ecological barriers, like the Saharan desert, where fuelling is very difficult, and large fuel loads have to be stored in advance. In this paper, we have investigated how seven species of birds are distributed in autumn close to the Saharan desert in the eastern Mediterranean area by using ring recoveries from northern Europe. The result clearly shows that the species included are not randomly distributed at this point, about 3,000 km from the breeding area. Birds from rather large breeding areas were shown to converge in confined areas, which in several cases completely differ between species. This means that birds of the same species have to follow different migratory directions depending on the location of their starting point. The observed pattern support earlier findings indicating that birds, in combination with a clock-and-compass orientation procedure, must use some external cues in order to find confined species-specific areas. The possibility for birds to use information from the Earth's magnetic field as an external cue in this area is discussed.