I examined the effects of nest site vegetation structure and cattle grazing on songbird nesting success in native mixed-grass prairie in Grasslands National Park of Canada and Mankota Community Pastures in southwestern Saskatchewan. This is the first study to compare songbird nesting success in season-long grazed and ungrazed native mixed-grass prairie. Sprague’s pipit, Baird’s sparrow, vesper sparrow, lark bunting, and chestnut-collared longspur all selected for denser vegetation at the nest than was generally available. Sprague’s pipit daily nest survival declined with increased vegetation density and litter depth at the nest site. Vegetative cover did not influence daily nest survival of the other species. Environmental conditions during the study may have resulted in an increased risk of predation for Sprague’s pipits nesting in greater cover. Grazing did not influence daily nest survival of any of the 5 species. Low-moderate intensity cattle grazing appears compatible with management for prairie songbirds in native mixed-grass prairie.

Temperate grasslands and the biodiversity they sustain are becoming increasingly imperilled. Habitat loss and degradation are considered primary causes of grassland species declines. Since livestock production is a dominant use of remaining temperate grassland, livestock producers and the grazing management decisions they make play a vital role in the recovery of grassland species. In this thesis, I examined social and ecological factors that drive habitat management and abundance of prairie wildlife species so as to contribute to conservation planning for prairie species at risk and their habitat. I focused on grassland songbirds because, of all prairie wildlife species, grassland birds have undergone some of the most dramatic declines in recent years. I employed an interdisciplinary approach, using theory and methodology from ornithology, rangeland management and the human dimension of conservation biology to achieve three objectives: i) to determine the extent to which indices of rangeland health explained variation in grassland songbird abundance for ten grassland bird species, including three species currently listed under Canada’s Species at Risk Act: Sprague’s pipit, McCown’s longspur and Chestnut-collared longspur; ii) to describe livestock producer characteristics, summarize producer awareness of and attitudes towards species at risk and the Canadian Species at Risk Act and evaluate how characteristics, awareness and attitudes affect producer willingness to engage in voluntary stewardship actions that support species at risk conservation; and iii) to explore relationships between select social and ecological factors and bird abundance for the three aforementioned grassland bird species at risk to elucidate novel pathways for achieving their conservation. I address the first objective in Chapter 2, where I identify the rangeland health index as a poor predictor of bird abundance and vegetation structure variables, such as litter and vegetation volume, as strong predictors of bird abundance. These findings make a case for further refining the rangeland health index as a tool for biodiversity assessment. In Chapter 3 I achieve the second objective and summarize producer characteristics, awareness and attitudes towards species. I also identify awareness, attitudes and rangeland management learning approach as important to producer willingness to support species at risk recovery. I accomplish the third objective in Chapter 4, where I present results of a structural equation model that upholds bird-habitat relationships identified in Chapter 2 and distinguishes management jurisdiction, size of land holdings and attitudes as important social factors to consider in conservation planning. Chapters 2 and 3 contribute to theory and methodology related to the ecological and social dimensions of grassland bird conservation, respectively. Chapter 4 demonstrates how structural equation models can be used to integrate social and ecological factors, and thereby inform habitat conservation and management. Both social and ecological data presented in this thesis make valuable contributions to producer engagement and habitat management aspects of conservation planning efforts for species at risk in the Milk River watershed of southwestern Saskatchewan. Overall, my findings point to the importance of a joint effort by regional private and public managers to use livestock grazing to create a mosaic of vegetation structure and habitat conditions suitable for the grassland bird community as a whole. This thesis provides a methodological approach that draws on and integrates social and ecological data, methods and concepts, thereby demonstrating how to conduct interdisciplinary research for biological conservation.

Livestock grazing impacts more land than any other use. Yet knowledge of grazing impacts on native fauna is scarce. This thesis takes a predictive approach to investigating the effects of livestock grazing on Australian woodland birds, employing some novel methodological approaches and experimental designs. These include methods of analysis to handle zero-inflated data and the application of Bayesian statistics to analyse predictions based on expert opinion. The experimental designs have enabled impacts of grazing to be separated from the frequently confounding effects of other disturbances, and to consider the effect of grazing on habitat condition in the context of different surrounding land uses. A distinguishing feature of many datasets is their tendency to contain a large proportion of zero values. It can be difficult to extract ecological relationships from these datasets if we do not consider how these zeros arose and how to model them. Recent developments in modelling zero-inflated data are tested with the aim of making such methods more accessible to mainstream ecology. Through practical examples, we demonstrate how not accounting for zero-inflation can reduce our ability to detect relationships in ecological data and at worst lead to incorrect inference. The impact of grazing on birds was first examined through the elicitation of a priori predictions from 20 Australian ecologists. This expert knowledge was then used to inform a statistical model using Bayesian methods. The addition of expert data through priors in our model strengthened results under at least one grazing level for all but one bird species examined. This study highlights that in fields where there is extensive expert knowledge, yet little published data, the use of expert information as priors for ecological models is a cost effective way of making more confident predictions about the effect of management on biodiversity. A second set of a priori predictions were formulated using a mechanistic approach. Habitat structure is a major determinant of bird species diversity and livestock grazing is one mechanism by which structure is altered. Using available information on the vegetation strata utilised by each species for foraging and the strata most affected by grazing, predictions of the impact of grazing on each bird species were formulated. We found that foraging height preference was a good predictor of species’ susceptibility to grazing. This approach is a starting point for more complex predictive models, and avoids the circularity of post hoc interpretation of impact data. The confounding of grazing with tree clearing was addressed by examining the impact of pastoral management on birds in sub-tropical grassy eucalypt woodland in Southeast Queensland, where land management practices have made it possible to disentangle these effects. Changes in bird species indices were recorded across woodland and riparian habitats with and without trees across three levels of grazing, replicated over space and time. Tree removal had a dramatic influence on 78% of the bird fauna. 65% of species responded significantly to changes in grazing level and the abundance of 42% of species varied significantly with habitat, level of clearing and grazing. The impact of grazing on birds was most severe in riparian habitat. Finally, the extent to which landscape context and local habitat characteristics influence bird assemblages of riparian habitats in grazed landscapes is addressed. Over 80% of bird species responded significantly to changes in local riparian habitat characteristics regardless of context, while over 50% of species were significantly influenced by landscape context. The influence of landscape context increased as the surrounding landuse became more intensive. These results suggest that it is not enough to conserve riparian habitats alone but conservation and restoration plans must consider landscape context. The ability to predict which bird species will be most affected by grazing will facilitate the transformation of this industry into one that is both profitable and ecologically sustainable. Results from this thesis suggest that any level of commercial grazing is detrimental to some woodland birds. Habitats with high levels of grazing support a species-poor bird assemblage dominated by birds that are increasing nationally. However, provided trees are not cleared and landscape context is not intensively used, a rich and abundant bird fauna can coexist with moderate levels of grazing, including iconic woodland birds which are declining elsewhere in Australia.

Made available in DSpace on 2014-06-11T19:35:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-08-21Bitstream added on 2014-06-13T20:26:43Z : No. of bitstreams: 1 gabriel_va_dr_rcla.pdf: 1465049 bytes, checksum: adbeba8c57d4586a7bcc4aae32986e9c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A expansão de plantações florestais tem sido intensificada nos últimos anos, ultrapassando 70.000.000 ha nos trópicos. Eucalyptus é o principal gênero plantado, ocupando 50% das áreas silviculturais. Monoculturas arbóreas e fragmentos de vegetação secundária figurarão entre os principais elementos das paisagens tropicais futuras. Logo, compreender como diversas espécies se comportam diante dessa situação é fundamental quando se objetiva a conservação da biodiversidade. Este trabalho estudou a avifauna em um mosaico composto por talhões de Eucalyptus spp. e alguns de vegetação nativa na Floresta Estadual Edmundo Navarro de Andrade (Rio Claro, SP). Esses talhões possuíam diferentes idades (plantados de 1934 a 1990), extensões (~1-51 ha) e graus de regeneração de vegetação nativa. Os principais objetivos foram caracterizar a avifauna encontrada nesses talhões quanto à riqueza, abundância e composição e compará-las, verificando possíveis associações com a estrutura da vegetação (riqueza, altura, área basal, densidade de plantas, densidade de plantas mortas, cobertura do dossel e densidade vertical nos estratos de 0,0 a 1,0, de 1,1 a 2,0 e de 2,1 a 5,0 m). Para a amostragem de aves foi empregado o método de pontos. No primeiro capítulo, foram amostrados 14 talhões de E. citriodora. Foram registradas 103 espécies de aves, variando de 23 a 55 por talhão. Myiodynastes maculatus, Cyclarhis gujanensis, Amazilia lactea e Megarynchus pitangua mostraram maior plasticidade ambiental, não revelando fortes associações com as variáveis da vegetação. A abundância total foi maior em talhões que apresentavam vegetação mais desenvolvida. Talhões com maior complexidade da vegetação apresentaram maior riqueza e abundância de espécies insetívoras e de dependentes de florestas. A distância entre os talhões de E. citriodora e de vegetação nativa... / The expansion of planted forests is surprisingly fast in the last years, exceeding 70.000.000 ha in the tropics, 50% of which are composed of Eucalyptus spp.. Planted and secondary forests are likely to be dominant features of tropical forest landscapes in the future. Therefore, to understand the use of different species in this situation in basic to the biological conservation. This work investigated the avifauna at a mosaic of Eucalyptus spp. patches in the State Forest Edmundo Navarro de Andrade (Rio Claro, Sâo Paulo, Brazil). These patches (~1-51 ha) were created in different years (1994-1990), presenting different levels of regeneration of the native vegetation. The principal aims were to evaluate the richness, abundance and composition of the bird community associating these parameters to the structure of the vegetation (richness, height, basal area, plant density, dead plant density, canopy cover and vertical density from 0,0 to 1,0, from 1,1 to 2,0 and form 2,1 to 5,0 m). The avifauna was sampled with point counts. In the first chapter, 14 patches of E. citrioddora were studied. It was recorded 103 species, from 23 to 55 per patch. Myiodynastes maculatus, Cyclarhis gujanensis, Amazilia lactea and Megarynchus pitangua were the most habitat generalist species. These species were not associated to any vegetation parameter. The abundance was greater in patches with more developed vegetation. Patches with high vegetation complexity had greater richness and abundance of insectivorous and forest dependent species. The distance between E. citriodora and native vegetation patches influenced negatively the richness and abundance of forest dependent species. In chapter 2, in addition to the 14 E. citriodora patches, four E. microcorys and three native vegetation patches were included in the analyses. It was recorded 115 species. On average, there were 47, 35 and 24 species in the patches... (Complete abstract click electronic access below)

The population dynamics of small mammal populations in Punda Maria, Kruger National Park, South Africa was investigated with respect to community size and structure, seed predation and dispersal of several trees. Species populations, community structure and habitat attributes were measured at six sites comprising of 3 habitat types (2 sites per habitat); namely Acaciagrassland, North-facing and South-facing sloped sites. Seasonal variation was investigated at the Acacia sites during late summer (April) and winter months (July). Five habitat attributes were measured; percentages of total cover and herbage, plant litter depth (cm), height of dominant vegetation type measured (m) and edaphic condition were recorded at 15 randomly selected traps per site. Almonds (Prunus dulcis), baobabs (Adansonia digitata), mopane (Colophospermum mopane), and Acacia tortilis seeds were used in the predation and dispersal experiment. North- and South-facing sites were dominated by Aethomys sp. while Acacia sites were dominated by Mastomys natalensis. Seed predation was high at the North-facing slopes, with a significant difference in predation on A. tortilis seeds. Seed dispersal activity was low; no , scatter hoarding was identified; only larder hoarding was observed by Aethomys sp. and M. natalensis at North-facing sites and Acacia sites respectively. Trampling by megaherbivore activity impacted vegetation structure and has negatively affected rodent population and ground activity, particularly at the Acacia sites.

Sediment and nutrient retention are important ecosystem functions floodplain meadows fulfil. While it is known that the inundated floodplain vegetation purifies the water during floods, little is known about the processes behind. I investigated the effect of the vegetation structure on sedimentation at three hierarchical scales, leaf, patch, and floodplain scale and used two approaches, experiments and an in situ field study. In the leaf experiment (study 1) I inundated single leaves into sediment rich water. The results showed that leaf pubescence increased sedimentation on leaf surfaces and that for leaves without hairs, the sedimentation increased with decreasing leaf area. In the flume experiment (study 2) I investigated the effects of community characteristics of vegetation patches regarding their capacity to capture sediment. I manipulated the leaf pubescence, the community density, the community height and the structural diversity (high-high vs high-low growing species) of the patches. The results show that all four investigated community characteristics increased the sediment retention. In the second flume experiment (study 3), I investigated the effect of species richness of vegetation patches on sediment retention. The results showed the importance of the vegetation biomass and identity effects of single species, but no clear effect of species richness. For the in situ field measurements (study 4), I measured sedimentation during a real flood event along the Mulde River in Germany. With sediment traps and biomass harvests I quantified the sedimentation underneath as well as on the vegetation. The results showed that besides the vegetation biomass, the topographical parameter ‘hydrological distance’ (pathway of lowest elevation the water travels to the site) is important for sediment and especially nutrient retention. Even though sediment retention is highest close by the river, sedimentation is still reasonably high far insight the floodplain and especially nutrient retention (C, N and P) increase with hydrological distance. From the sum of results I can derive four management strategies for floodplains to increase the sediment retention. First, reduced mowing for more standing biomass during flood season, wherefore trade-offs with other ecosystem functions need to be evaluated carefully. Second, promotion of structural diversity, possible via species diversity. Third, promotion of species with characteristics that increase sediment, such as pubescent leaves. Forth, preserving or recreating topographic complexity in the floodplain. Overall, I showed that the specific structures of herbaceous vegetation are highly beneficial for sediment and nutrient retention on floodplains.:Table of contents 1. General introduction 6 1.1 The Mulde River and the “Wilde Mulde” project 7 1.2 Sediment retention on floodplains 8 1.3 Vegetation causes fine sedimentation 11 1.4 Structural characteristics 12 1.4.1 Structural identity of species 13 1.4.2 Structural identity of communities 14 1.4.3 Structural diversity of communities 15 1.5 Links between studies 17 2. Methodological features 19 2.1 Study area “Wilde Mulde” 19 2.2 Leaf roughness measurement 22 2.3 Experimental set up of the flume experiment 24 3. Original contributions 26 3.1 Paper 1 - Leaf area and pubescence drive sedimentation on leaves surfaces during flooding 26 3.2 Paper 2 – Plant structural diversity alters sediment retention on and underneath herbaceous vegetation in a flume experiment 44 3.3 Paper 3 – Effects of plant species identity overrides diversity effects in explaining sedimentation within vegetation in a flume experiment 65 3.4 Paper 4 – Vegetation characteristics control sediment and nutrient retention on but not underneath vegetation in floodplain meadows 77 4. Discussion 107 4.1 Mechanistic parallels among scales 109 4.2 Effects of species diversity in relation to species identity 112 4.3 Transferability and its limitations 113 4.4 The ecosystem function of sediment retention 114 4.4.1 Floodplain management for sediment retention 115 4.4.2 Sediment retention in the context of other ecosystem functions 117 4.4.3 Floodplain management for sediment retention along the Lower Mulde River 119 5. Outlook 122 5.1 Leaf roughness 122 5.2 Diversity experiment 123 5.3 Approaches for new management strategies 124 5.4 Extrapolation with remote sensing 125 5.5 Sediment budget 126 6. Conclusion 128 7. References 130 8. Summary 143 9. Zusammenfassung 149 Acknowledgements 155 Author contribution statement 156 Curriculum vitae 164 List of publications 166 Selbstständigkeitserklärung 169

Examination of bird assemblages along an environmental gradient which encompasses both climate and habitat change is needed if we are to better understand the potential effects of these changes for avians and the ecological process that depend upon them. Climate change is predicted to have a significant impact on deserts and desert margins, resulting in distributional shifts of entire ecosystems and new community associations. This study explores the probable responses of avian communities to increasing desertification. In general, species richness and numbers of birds in arid zones are low compared to more mesic areas. Different combinations of habitat types and the variety of patches in a landscape influence the diversity and community structures of avians in that landscape. The role of vegetation structure in avian habitat selection in semi-arid areas is dictated by horizontal habitat density as well as vertical structure. Although bird distribution is determined by habitat boundaries, most birds are flexible and can disperse across small habitat barriers. The hypothesis tested, was that bird species assemblages along an aridity gradient are affected primarily by rainfall and secondarily by habitat type. Assessing the impacts of rainfall and habitat on bird variables, such as species richness, abundance, diversity, biomass, and life history traits, were the objectives of the study. An east-west aridity gradient of 300 mm, stretching over 370 km, was chosen in central Namibia for the study area. The climate is harsh with localised rain and considerable daily fluctuations in temperature. Grasses, and trees and shrubs up to 7 m in height are the co-dominant life-forms. Surveys were conducted over three years; one winter and one summer survey in each year. Rainfall, seasons and vegetation height were recorded as environmental variables. Three structurally different habitat types were selected for stratified sampling: open areas, rivers and thickets. Open areas were dominated by grass; river refers to ephemeral dry river lines with mature trees; and thickets comprise woody shrubs and trees. At each site, the same three habitats were used for bird sampling, resulting in 15 sample units. Sampling took place on 51 discontinuous line transects of 1km in length and without a width limit. Univariate analyses included ANOVA and t-tests. Multivariate analyses consisted of cluster analysis, MRPP tests, indicator analysis, Shannon diversity index and NMS ordinations. NMS bi-plots were used to define avian community structures responding to aridity, habitat, migration and life history traits. The results showed that bird species richness, abundance, and diversity remained relatively constant across the aridity gradient, until they declined significantly once a certain aridity threshold was crossed at the most arid site. There were significantly more bird species and individual birds at the wetter sites than at the drier sites. Rivers contained more birds than thickened or open habitat types, suggesting the importance of riparian habitat types for maintaining avian diversity. The three more mesic sites included higher numbers of species from the nesting and feeding guilds, regardless of habitat type, than the two more arid sites. The aridity threshold had a significant effect on bird community structures: more migrant and nomadic species, and omnivore and insectivore species persisted in very arid conditions. From the results it was predicted that climate change will cause avian species to undergo range shifts from west to east, resulting in community composition changes and a reduction in diversity. Life history traits affect the adaptive capabilities of bird species and it is predicted that nomadism, flexibility in diet, and adaptability of nesting requirements will contribute to species persistence in the drier conditions predicted under current climate change scenarios. Dry river lines will act as refugia for avian diversity, but crucial habitat types that currently contain less diversity are also important for maintaining unique avian assemblages. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Examination of bird assemblages along an environmental gradient which encompasses both climate and habitat change is needed if we are to better understand the potential effects of these changes for avians and the ecological process that depend upon them. Climate change is predicted to have a significant impact on deserts and desert margins, resulting in distributional shifts of entire ecosystems and new community associations. This study explores the probable responses of avian communities to increasing desertification. In general, species richness and numbers of birds in arid zones are low compared to more mesic areas. Different combinations of habitat types and the variety of patches in a landscape influence the diversity and community structures of avians in that landscape. The role of vegetation structure in avian habitat selection in semi-arid areas is dictated by horizontal habitat density as well as vertical structure. Although bird distribution is determined by habitat boundaries, most birds are flexible and can disperse across small habitat barriers. The hypothesis tested, was that bird species assemblages along an aridity gradient are affected primarily by rainfall and secondarily by habitat type. Assessing the impacts of rainfall and habitat on bird variables, such as species richness, abundance, diversity, biomass, and life history traits, were the objectives of the study. An east-west aridity gradient of 300 mm, stretching over 370 km, was chosen in central Namibia for the study area. The climate is harsh with localised rain and considerable daily fluctuations in temperature. Grasses, and trees and shrubs up to 7 m in height are the co-dominant life-forms. Surveys were conducted over three years; one winter and one summer survey in each year. Rainfall, seasons and vegetation height were recorded as environmental variables. Three structurally different habitat types were selected for stratified sampling: open areas, rivers and thickets. Open areas were dominated by grass; river refers to ephemeral dry river lines with mature trees; and thickets comprise woody shrubs and trees. At each site, the same three habitats were used for bird sampling, resulting in 15 sample units. Sampling took place on 51 discontinuous line transects of 1km in length and without a width limit. Univariate analyses included ANOVA and t-tests. Multivariate analyses consisted of cluster analysis, MRPP tests, indicator analysis, Shannon diversity index and NMS ordinations. NMS bi-plots were used to define avian community structures responding to aridity, habitat, migration and life history traits. The results showed that bird species richness, abundance, and diversity remained relatively constant across the aridity gradient, until they declined significantly once a certain aridity threshold was crossed at the most arid site. There were significantly more bird species and individual birds at the wetter sites than at the drier sites. Rivers contained more birds than thickened or open habitat types, suggesting the importance of riparian habitat types for maintaining avian diversity. The three more mesic sites included higher numbers of species from the nesting and feeding guilds, regardless of habitat type, than the two more arid sites. The aridity threshold had a significant effect on bird community structures: more migrant and nomadic species, and omnivore and insectivore species persisted in very arid conditions. From the results it was predicted that climate change will cause avian species to undergo range shifts from west to east, resulting in community composition changes and a reduction in diversity. Life history traits affect the adaptive capabilities of bird species and it is predicted that nomadism, flexibility in diet, and adaptability of nesting requirements will contribute to species persistence in the drier conditions predicted under current climate change scenarios. Dry river lines will act as refugia for avian diversity, but crucial habitat types that currently contain less diversity are also important for maintaining unique avian assemblages. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Student Number : 9202137P - MSc Dissertation - School of Animal, Plant and Environmental Studies - Faculty of Science / The Reconstruction and Development Programme’s Mpumalanga Working for Water Programme (WWP) has cleared exotic and commercial weed species from the riverine environment since 1994. This study serves as an assessment of the impact and modification caused as a result of invasion and the subsequent clearing of the exotic vegetation on flora in the riverine zone of the Sabie River Catchment. The experimental design compares the before and after clearing effects and includes altitude and invasion intensity variables. The investigations included: in situ soil seed banks, environmental modification, vegetation structure, species diversity and effectiveness of clearing. Clearing and invasion by exotic species altered soil chemical, physical and ground cover parameters. The extent of these modifications was dependent on the extent of invasion and clearing done within the community. Clearing of exotic species however, acted as an additional disturbance to that caused by invasion. Environmental modifications that occurred with clearing and invasion within the study were positively related to percentage soil organic matter, and ground cover (soil, litter, vegetation). Invasion by exotic species alters the vegetation structure, the extent of which was directly related to the invasion intensity. The main source of vegetation structure modification is attributed to tall growing exotic species such as Eucalyptus grandis and Solanum mauritianum. Both of these species dominated the indigenous vegetation, E. grandis by expanding the upper canopy and S. mauritianum by dominating the mid canopy. Clearing of invasive vegetation resulted in an additional disturbance proportional to the extent of invasion intensity. Invasion did not result in any large changes to the vegetation at low intensity but clearing at this intensity increased the disturbance and altered the vegetation structure. Soil seed banks were limited in the number of species and dominated by two exotic species. The soil seed bank of woody species related positively to the community species richness. The total soil seed bank density did not relate to invasion intensity or clearing thereof but propagules of individual species within the soil seed banks did. The seeds of the exotic species, Acacia mearnsii and S. mauritianum, illustrated burial as prerequisite for persistence in the soil seed bank. A. mearnsii and S. mauritianum seeds were found to have half-life’s of up to 25 years and 13 months respectively. The species richness and diversity varied only marginally because of invasion and clearing. Species alpha diversity increased with clearing due to weedy and pioneer species establishment. Beta diversity effectively highlights the species turnover with clearing and invasion. Success in eradication of exotic species had mixed results. Clearing of high invasion sites was effective but in lower invasion categories a number of exotic individuals were missed. Clearing effectiveness was good for certain species such as E. grandis and Pinus patula, but poor for others such as S. mauritianum. Coppicing is a significant issue for E. grandis and S. mauritianum. The persistence of individuals (coppicing & missed individuals) coupled with very large persistent seed banks has repercussions for the clearing programme, as it may prevent effective eradication. Initially the WWP has been successful in removing exotic vegetation, however there is a failure to address the regenerative properties of some exotic species. Unless a rigid schedule of follow up clearing treatments occurs, an even larger invasion problem could exist.

Esse estudo teve como objetivo investigar os fatores estruturantes das taxocenoses de aves que utilizam remanescentes de vegetação campestre na região da Fronteira Oeste do Rio Grande do Sul. Através desse estudo busquei compreender os efeitos da estrutura espacial dos remanescentes (área, formato e proximidade entre remanescentes) e também os efeitos exercidos pela estrutura do habitat no uso desses pelas aves campestres. Amostrei quantitativamente por pontos de contagem a avifauna em 21 manchas de vegetação campestre com diferentes áreas, formas e estrutura da vegetação. Utilizei ferramentas de sensoriamento remoto para avaliar a estrutura espacial dos remanescentes e caracterizei o habitat dessas manchas através de medidas da estrutura da vegetação. Utilizei o método analítico de partição da variância através de análises de regressão múltipla e análise de correlação canônica parciais para quantificar a porção da variância explicada por cada grupo de variáveis (estrutura da vegetação e estrutura espacial dos remanescentes) na variação total da abundância, composição e riqueza da avifauna nas manchas. Registrei um total de 33 espécies de aves campestres, sendo três dessas categorizadas em algum grau de ameaça de extinção: Circus cinereus, Cisthotorus platensis e Sporophila cinnamomea. Meus resultados indicaram que a estrutura espacial das manchas não exerce efeito significativo sobre a avifauna campestre e a essa responde principalmente à estrutura e características da vegetação. Dessa forma, meus resultados sugerem que as assembléias de aves que utilizam os remanescentes de vegetação campestre da região estudada são estruturadas a partir das características do habitat e são fracamente influenciadas pela estruturação espacial desses. Assim, a permanência de manchas próximas de vegetação campestre em meio às áreas de cultivo, mesmo que pequenas, poderá favorecer a permanência de uma alta diversidade de espécies de aves na região estudada. / The goal of this study was to investigate the factors that structure bird assemblages in grassland patches in Campos Biome of Fronteira Oeste region, Rio Grande do Sul, Brazil. Thus, I searched for the effects of the spatial structure of native vegetation patches and the effects caused by their vegetation structure on the avifauna that makes use of them. I utilized remote sensing techniques to evaluate the spatial structure of the patches (area, shape, and proximity among patches) and I characterized the patches’ habitat by measuring the vegetation structure (vegetation height, dead standing vegetation, soil covered by vegetation, percentage coverage by grasses, herbs, and shrubs). I used the variation partitioning method to quantify the portion of variation explained by both spatial and vegetation group of variables in the total avifauna’s abundance, composition, and richness variation. I registered 33 grassland bird species and among them, three are threatened with extinction: Circus cinereus, Cisthotorus platensis, and Sporophila cinnamomea. My results denote an insignificant effect of spatial structure of patches on the grassland birds and a high response to the vegetation structure. In this way, my results suggest that the grassland bird’s assemblages that use native vegetation patches are mainly structured by the habitat characteristics (vegetation structure), and are weakly influenced by the patches spatial arrangement. Thus, the maintenance of neighbour patches, even though small ones, into the arable fields may favour the persistence of a high diversity of grassland birds in the region studied.