Landscape effects on birds in urban woodlands: an analysis of 34 Swedish cities

Aim To compare bird abundances in woodlands along gradients from the city centre to the peri‐urban area. To evaluate the importance of the proportion of woodland within the city and in the peri‐urban landscape to forest bird communities breeding in urban woodlands. To test whether fragmentation effects on birds were linked to the type of peri‐urban matrix. Location A total of 34 Swedish cities with > 10,000 inhabitants in south‐central Sweden. The study area covered 105,000 km², in which 84% of the Swedish population of 9.1 million lives. Methods Repeated point count surveys were conducted in 2004 in a total of 474 woodlands. General linear models were used to test for possible differences in abundance along urban to peri‐urban gradients, and to regress bird abundances in local urban woodlands on: (1) total woodland cover in the city, (2) total woodland cover in the peri‐urban landscape, (3) the interaction between woodland cover in the city and in the peri‐urban area, (4) region, and (5) human density. Results More than 12,000 individuals of 100 forest bird species were recorded. Of the 34 most common species detected, 13 bird species had higher abundances in urban than in peri‐urban woodlands, and seven species showed the opposite trend. The bird community of urban woodlands was characterized by species associated with deciduous forests and tree nesters, whereas the bird community of peri‐urban woodlands was characterized by species associated with coniferous woodland and ground nesters. Twelve species were significantly linearly associated with the proportion of urban woodland and/or the proportion of peri‐urban woodland, and a further eight species were associated with the interaction between these two factors. Local breeding bird abundances of four species were significantly positively associated with the proportion of urban woodland only in farmland‐dominated landscapes. Main conclusions Fragmentation effects on some urban birds are linked to the type of peri‐urban matrix. In farmland landscapes, peri‐urban woodlands may have been too scarce to act as a source of bird immigrants to fragmented urban woodlands. To maintain populations of specialized forest birds within cities in landscapes dominated by agriculture, it is of paramount importance to conserve any remaining urban woodlands.     

Mechanisms of population dynamics in trans-Saharan migrant birds: A review

Modern views on the mechanisms of population dynamics in Palearctic birds wintering in tropical Africa are discussed with regard to the distribution of migrants on the African continent and the influence of external factors on conditions of bird wintering. The data on long-term bird trapping at ten ornithological stations in Europe are analyzed. Among 142 long-term trends in the population dynamics of 18 bird species, 34% are negative, 11% are positive, and the remaining trends lack statistical significance. The proportion of negative trends in each species negatively correlates with the number of birds: the more abundant the species, the lower the probability of its long-term population decline. Population dynamics may largely be determined by environmental conditions in wintering regions. Population studies on ten Palearctic species showed that drastic population declines and even local extinction of birds in recent decades resulted from the dramatic decrease in their survival on African wintering grounds because of insufficient precipitation and, in particular, severe droughts in the Sahel.     

Bird species richness and densities in relation to sulphur dioxide gradients and environmental variables

The expansion of coal-fired power stations in South Africa has resulted in growing environmental concerns as they are the largest emitters of sulphur dioxide (SO₂). Sulphur dioxide emissions from power plants pose a potential threat to avian populations. However, the effect of SO₂ pollution on bird communities is poorly understood. Using point counts we investigated the relationships of bird species richness and species-specific density with SO₂ concentrations around Matimba power station. Environmental parameters were derived from remotely sensed data and data reduction was performed using principal component analysis. Generalised linear mixed models were then used to infer the relationships of bird species richness and species-specific densities with SO₂ concentrations and the environmental variables. Our results revealed that SO₂-polluted air had no influence on bird species richness and densities in our study sites, but SO₂ levels were below annual national ambient air quality standards. Vegetation productivity was found to have a greater influence on species densities than SO₂ pollution. Monitoring of bird population changes around Matimba power station once neighbouring Medupi power station is fully operational is recommended, as SO₂ content of the air will increase significantly, and species may be sensitive to this increase in SO₂ levels.     

Urban bird trends in a rapidly growing tropical city

Long-term studies of urban birds are relatively scarce, especially in Africa. We analysed trends in species richness and bird species occurrence over a 32-year period in Kampala, Uganda, in order to assess changes in the bird community in a period that has shown rapid expansion of the city's human population. Given that species may respond to urbanisation according to their diet, we also analysed bird community trends of species groups defined according to predominant diet. There was an overall decline in species richness that was largely driven by declines in insectivores and granivores. General declines were evident also when the trends in the most common individual species in these two groups were considered. The occurrence of the commonest predator and scavenger species tended to increase over the period considered. Insectivorous species are likely to be especially affected by increasing urbanisation due to air pollution. Predators and scavengers are likely to have benefitted from the inability of municipal waste management to keep pace with growth in the human population, hence providing more potential food resources. Both insectivores and predators/scavengers are therefore good candidates for the development of urban indicators.     

Geographic variation in the population trends of common breeding birds across central Europe

Recent declines of many European bird species have been linked with various environmental changes, especially land-use change and climate change. Since the intensity of these environmental changes varies among different countries, we can expect geographic variation in bird population trends. Here, we compared the population trends of bird species among neighbouring countries within central Europe (Czech Republic, Denmark, Germany, Switzerland) between 1990 and 2016 and examined trait-associations with population trends at both national and international scales. We found that Denmark had the highest proportion of declining species while Switzerland had the lowest. Species associated with farmland had negative trends, but the effect size tended to differ among countries. A preference for higher temperature was positively associated with population trends and its effect size was similar among countries. Species that were increasing across all four countries were associated with forest; while species that were decreasing across all countries were long-distance migrants or farmland birds. Our results suggest that land-use change tends to be a more regionally variable driver of common bird population trends than climate change in central Europe. For species declining across all countries, international action plans could provide a framework for more efficient conservation. However, farmland birds likely need both, coordinated international action (e.g. through a green agricultural policy) to tackle their widespread declines as well as regionally different approaches to address varying national effect trajectories.     

中国鸟类红色名录评估

中国有1,372种鸟类, 其中77种为中国特有。由于资源过度利用、栖息地丧失和片断化、环境污染等原因, 中国的鸟类多样性保护面临严峻的挑战。为了全面评估当前中国野生鸟类的濒危状况, 国家环境保护部支持启动了“中国脊椎动物红色名录”的编制工作。依照IUCN的标准, 对中国鸟类的受胁状况进行了一次全面评估。通过确定评估对象、数据收集、初评、初核、复审、定稿等步骤, 集国内27位鸟类学家的力量, 完成了本次评估。结果表明: 区域灭绝(RE)3种, 分别是白鹳(Ciconia ciconia)、镰翅鸡(Falcipennis falcipennis)和赤颈鹤(Grus antigone), 极危(CR)15种, 濒危(EN)51种, 易危(VU)80种, 近危(NT)190种; 无危(LC)876种, 数据缺乏(DD)157种。列为极危、濒危和易危等级的受胁鸟类合计146种, 占中国鸟类种数的10.6%。受威胁程度最高的科是鹈鹕科和犀鸟科, 这两个科100%的物种都属于受胁种。。77种特有鸟类中有29种(37.7%)属于受胁种。陆禽和猛禽是受胁最严重的生态类群, 分别有25.2%和23.2%的种类处于受胁状态。不同行政区域受胁鸟类差异较大。本工作对于我国鸟类保护和履行国际公约等工作均有重要意义。     

Variations of the germinable soil seed bank along the altitudinal gradient in the northwestern Red Sea region

In a mixed forest in Hong Kong, the foraging ecology of nine species of insectivorous birds was studied. Leaves and branches of diameters smaller than 2 cm were the most frequently searched microhabitats. Gleaning was the most frequently used foraging method. Apart from Blue-winged Minla and Japanese White-eye, no two species used similar proportions of vertical strata and microhabitats at the same time. Bird species using similar proportion of microhabitats were foraging in different proportion of vertical strata. This niche segregation enabled the bird species to coexist in the same habitat. Velvet-fronted Nuthatch differed from other species by its more frequent use of branches of diameters larger than 2 cm and tree trunks. This might be one of the reasons why this exotic species successfully established a breeding population in the study area.     

Decomposing trends in bird populations: Climate,life histories and habitat affect different aspects of population change

Aim

Despite the complexity of population dynamics, most studies concerning current changes in bird populations reduce the trajectory of population change to a linear trend. This may hide more complex patterns reflecting responses of bird populations to changing anthropogenic pressures. Here, we address this complexity by means of multivariate analysis and attribute different components of bird population dynamics to different potential drivers.

Location

Czech Republic.

Methods

We used data on population trajectories (1982–2019) of 111 common breeding bird species, decomposed them into independent components by means of the principal component analysis (PCA), and related these components to multiple potential drivers comprising climate, land use change and species' life histories.

Results

The first two ordination axes explained substantial proportion of variability of population dynamics (42.0 and 12.5% of variation in PC1 and PC2 respectively). The first axis captured linear population trend. Species with increasing populations were characterized mostly by long lifespan and warmer climatic niches. The effect of habitat was less pronounced but still significant, with negative trends being typical for farmland birds, while positive trends characterized birds of deciduous forests. The second axis captured the contrast between hump-shaped and U-shaped population trajectories and was even more strongly associated with species traits. Species migrating longer distances and species with narrower temperature niches revealed hump-shaped population trends, so that their populations mostly increased before 2000 and then declined. These patterns are supported by the trends of total abundances of respective ecological groups.

Main Conclusion

Although habitat transformation apparently drives population trajectories in some species groups, climate change and associated species traits represent crucial drivers of complex population dynamics of central European birds. Decomposing population dynamics into separate components brings unique insights into non-trivial patterns of population change and their drivers, and may potentially indicate changes in the regime of anthropogenic effects on biodiversity.     

Estimating regional landbird populations from enhanced North American Breeding Bird Surveys

Estimating the size of bird populations is central to effective conservation planning and prudent management. I updated estimated regional bird populations for the East Gulf Coastal Plain of Mississippi using data from 275 North American Breeding Bird Surveys from 2009 to 2013. However, regional bird populations estimated from count surveys of breeding birds may be biased due to lack of empirical knowledge of the distance at which a species is effectively detected and the probability of detecting a species if it is present. I used data recorded within two distance classes (0–50 m and >50–400 m) and three 1‐min time intervals on 130 Breeding Bird Surveys to estimate detection probability and effective detection distance for 77 species. Incorporating these empirical estimates of detection probability and detection distance resulted in estimated regional populations for these species that were markedly greater than regional populations estimated without species‐specific estimates of detection parameters. Using the same Breeding Bird Survey data, I also estimated probability of site occupancy for 66 species and extrapolated this to the proportion of area occupied in the East Gulf Coastal Plain of Mississippi. I combined the area occupied with the reported range of breeding territory size for 54 species to obtain independent estimates of regional bird populations. Although the true population of these species is unknown, estimated populations that incorporated empirical estimates of detection probability and detection distance were more likely to be within the range of independently estimated, occupancy‐based, regional population estimates than were population estimates that lacked empirical detection and distance information.     

Predators at bird nests in a northern hardwood forest in New Hampshire

ABSTRACT.   Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure.     

Bird population in birch forests of the Southern Urals affected by industrial pollution: Report 2. Relationship with habitat variables

The changes in habitat variables are analyzed according to the data of 2009 at ten sites along the gradient of pollution by emissions from the Karabash Copper Smelter (Chelyabinsk oblast): the pollution level, basic structural characteristics of phytocenosis, and abundance of leaf-eating invertebrates and epigeic invertebrates. The height of the top canopy, stand basal area, foliage cover of all forest layers, and biomass of epigeic invertebrates decrease as pollution grows. Foliar damage in birch (the indirect index of the abundance of phyllophages) changes only insignificantly. It seems impossible to differentiate the contribution of abiotic and biotic variables to the formation of the bird population in the study region because of close correlation between them. Pollution seems to affect the bird population indirectly through the changes in habitats.     

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.     

The impact of shrub encroachment on savanna bird diversity from local to regional scale

Aim  Evidence is accumulating of a general increase in woody cover of many savanna regions of the world. Little is known about the consequences of this widespread and fundamental ecosystem structural shift on biodiversity.
Location  South Africa.
Methods  We assessed the potential response of bird species to shrub encroachment in a South African savanna by censusing bird species in five habitats along a gradient of increasing shrub cover, from grassland/open woodland to shrubland dominated by various shrub species. We also explored historical bird species population trends across southern Africa during the second half of the 20th century to determine if any quantifiable shifts had occurred that support an ongoing impact of shrub encroachment at the regional scale.
Results  At the local scale, species richness peaked at intermediate levels of shrub cover. Bird species composition showed high turnover along the gradient, suggesting that widespread shrub encroachment is likely to lead to the loss of certain species with a concomitant decline in bird species richness at the landscape scale. Finally, savanna bird species responded to changes in vegetation structure rather than vegetation species composition: bird assemblages were very similar in shrublands dominated by Acacia mellifera and those dominated by Tarchonanthus camphoratus .
Main conclusions  Shrub encroachment might have a bigger impact on bird diversity in grassland than in open woodland, regardless of the shrub species. Species recorded in our study area were associated with historical population changes at the scale of southern Africa suggesting that shrub encroachment could be one of the main drivers of bird population dynamics in southern African savannas. If current trends continue, the persistence of several southern African bird species associated with open savanna might be jeopardized regionally.     

合肥市小微湿地鸟类多样性的时空格局及其影响因素

小微湿地是城市生态系统的重要组成部分, 也是生物多样性的重要庇护场所。鸟类作为城市小微湿地生态系统的指示类群, 其多样性时空格局受多种环境因子影响。本研究于2020年8月至2021年7月采用样点法对合肥市45个小微湿地鸟类的种类、数量分布和生境因子进行了调查, 并获取湿地面积、湿地形状、建筑面积比例、植被面积比例、环境噪声、人为干扰和城市化指数等生境变量。通过α多样性和β多样性分析, 研究城市小微湿地鸟类多样性的时空特征及其决定因素。采用信息论模型选择和模型平均法以及基于距离矩阵的多重回归模型进行计算, 确定影响鸟类群落α多样性和β多样性及其组分的主要环境因子。结果显示, 研究区域共有鸟类13目39科102种, 其中水鸟31种, 国家二级重点保护鸟类2种, 安徽省重点保护鸟类17种, IUCN濒危物种红色名录中的易危(VU)物种1种。湿地面积和城市化指数对小微湿地陆地鸟类和水鸟的α多样性、β多样性及其组分均具有显著影响, 其中陆地鸟类物种丰富度在中度和低度城市化之间的小微湿地中达到最高值, 面积超过4 ha的小微湿地能维持较多的水鸟物种。植被面积比例对陆地鸟类多样性具有重要的影响, 而建筑面积比例对水鸟多样性具有显著影响。此外, 总体β多样性及其组分计算结果显示物种周转组分占明显优势, 表明城市小微湿地群作为城市复合生态系统的重要组成部分, 加强整体保护更为必要。研究结果对于加强城市鸟类保护和提高城市生态环境质量具有指导意义。     

Patterns of endemic extinctions among island bird species

The relationship between island biogeography and the vulnerability of island biota to extinction as a result of human activities was examined. In particular, this study analyzed whether island area, maximum elevation of an island, isolation from the nearest continental landmass, or date of human colonization had statistically significant relationships with the proportion of endemic island bird species that have become endangered or extinct. The study examined islands or island groups with endemic bird species, and which have never been connected to a continental landmass. Both modern and fossil bird species were incorporated into the analysis. Islands that were colonized by humans earliest had the lowest proportion of modern species alone, and modern and fossil species combined, that have gone extinct. However, date of human arrival was not correlated with the proportion of modern species that are endangered. Maximum elevation of an island was negatively correlated with the proportion of modern species that are extinct, and was positively correlated with the proportion of modern species that are endangered. Area was negatively correlated with the proportion of modern species that are endangered. Isolation of islands was not significantly correlated with the proportion of modern species extinct or endangered, but was positively correlated with the proportion of modern and fossil species combined that have gone extinct. These results indicate that the initial spasm of island bird extinctions due to human contact may have, in part, passed. They also indicate that bird species on islands colonized earliest by humans may have had more time to adapt to the presence of man and his commensal species, resulting in reduced extinction rates.     

The urban decline of the house sparrow (Passer domesticus): a possible link with electromagnetic radiation

During recent decades, there has been a marked decline of the house sparrow (Passer domesticus) population in the United Kingdom and in several western European countries. The aims of this study were to determine whether the population is also declining in Spain and to evaluate the hypothesis that electromagnetic radiation (microwaves) from phone antennae is correlated with the decline in the sparrow population. Between October 2002 and May 2006, point transect sampling was performed at 30 points during 40 visits to Valladolid, Spain. At each point, we carried out counts of sparrows and measured the mean electric field strength (radiofrequencies and microwaves: 1 MHz-3 GHz range). Significant declines (P = 0.0037) were observed in the mean bird density over time, and significantly low bird density was observed in areas with high electric field strength. The logarithmic regression of the mean bird density vs. field strength groups (considering field strength in 0.1 V/m increments) was R = -0.87 (P = 0.0001). The results of this article support the hypothesis that electromagnetic signals are associated with the observed decline in the sparrow population. We conclude that electromagnetic pollution may be responsible, either by itself or in combination with other factors, for the observed decline of the species in European cities during recent years. The appearently strong dependence between bird density and field strength according to this work could be used for a more controlled study to test the hypothesis.     

Evaluating the effectiveness of overstory cover as a surrogate for bird community diversity and population trends

Landscape features are often used as surrogates for biodiversity. While landscape features may perform well as surrogates for coarse metrics of biodiversity such as species richness, their value for monitoring population trends in individual species is virtually unexplored. We compared the performance of a proposed habitat surrogate for birds, percentage cover of vegetation overstory, for two distinct aspects of bird assemblages: community diversity (i.e. species richness) and population trends. We used four different long-term studies of open woodland habitats to test the consistency of the relationship between overstory percentage cover and bird species richness across a large spatial extent (>1000 km) in Australia. We then identified twelve bird species with long-term time-series data to test the relationship between change in overstory cover and populations trends. We found percentage cover performed consistently as a surrogate for species richness in three of the four sites. However, there was no clear pattern in the performance of change in percentage cover as a surrogate for population trends. Four bird species exhibited a significant relationship with change in percentage overstory cover in one study, but this was not found across multiple studies. These results demonstrate a lack of consistency in the relationship between change in overstory cover and population trends among bird species, both within and between geographic regions. Our study demonstrates that biodiversity surrogates representing community-level metrics may be consistent across regions, but provide only limited information about individual species population trends. Understanding the limitations of the information provided by a biodiversity surrogate can inform the appropriate context for its application.     

Habitat heterogeneity drives bird species richness,nestedness and habitat selection by individual species in fluvial wetlands of the Paraná River,Argentina

We assessed the relationship between habitat heterogeneity and bird species richness and composition within wetlands of the floodplain of the Middle Paraná River, Argentina. Given the high habitat heterogeneity in these wetland systems, we sought to determine whether (i) there was a positive relationship between bird species richness and habitat heterogeneity; (ii) whether bird species richness was associated with certain types of individual habitat types; (iii) whether there was a pattern of species nestedness and turnover between sites as a function of habitat heterogeneity and composition, respectively; and (iv) whether individual species exhibited associations with habitat heterogeneity. Point counts were used to survey birds at 60 sites. We estimated the area of eight habitat types found within a 200‐m radius from the centre of each site and calculated number and Pielou's evenness of habitat types. These indices, together with area proportion of each habitat type, were used as explanatory factors of bird species richness in linear regression models. Habitat heterogeneity per se rather than area of individual habitat types was a more important predictor of species richness in these fluvial wetlands. Sites with more habitat types supported more bird species. Results showed that individual bird species were associated with different habitat types and, therefore, sites that contained more habitat types contained more species. Number of habitat types accounted for species nestedness between sites whereas composition of habitat types accounted for species turnover between sites. Results suggest that selection of heterogeneous sites by individual species could help explain the positive heterogeneity–species richness relationship. Our findings highlight the importance of habitat heterogeneity per se resulting from flood disturbances in maintaining bird richness in fluvial systems.     

Modelling irruptions and population dynamics of the great spotted woodpecker – joint effects of density and cone crops

Irruptive migrants are partially migrating species showing pronounced temporal variation in the number of migrants. Occasional irruptions are often explained by increased population density (per area) or lack of food. Similarly to population dynamics, these explanations are not mutually exclusive, but probably act in concert. Here we do a parallel analysis on the migration intensity and population dynamics of an irruptive migratory bird species, the great spotted woodpecker Dendrocopos major, in southern Finland. Both analyses include simultaneous effects of breeding density and cone crops of Scots pine Pinus sylvestris and Norway spruce Picea abies. A novel model for statistical analyses of irruptive migration intensity is developed. Population dynamics are investigated using log‐linear state‐space models. Woodpecker migration intensity is well explained by lack of spruce cones and increases proportionally to population density. Population dynamics is most successfully described with a density dependent model, where the natural logarithm of spruce cone availability previous autumn has a strong positive effect on population growth. This is likely to be due to lowered winter mortality and lowered emigration rates resulting from plentiful food availability. Although the species uses pine cones as a food resource in winter, the estimated impacts of pine cone crops on migration intensity and population dynamics are low, probably due to low annual variation in crop comparing to spruce cones. Large irruptions also tend to occur earlier in season, often before cones are a crucial food resource for the woodpeckers, suggesting that the woodpeckers use the amount of maturing cones as a cue for upcoming conditions. Our results show that the ecological role of different resources can differ considerably from the expected pattern based on the proportion of the resources in a species’ diet. Advantages of examining patterns of bird migration, population density and dynamics in unison are apparent.     

Comparison of structure and biodiversity in the Rajhenav virgin forest remnant and managed forest in the Dinaric region of Slovenia

Comparisons are made between a virgin forest remnant (primeval forest) and a lightly managed (near‐to‐nature) forest with regard to horizontal forest structures, the structure of forest stands, and the diversity of plant and bird species. In the virgin forest remnant the proportion of canopy gaps is smaller, there are no stands in the developmental phase of a pole stand (10 < cm d.b.h. < 30 cm), and both the growing stock and the proportion of less vigorous trees are considerably greater. In addition, there is a higher percentage of dead trees, a smaller proportion of minor tree species and a considerably lower diversity of plants. The diversity of bird species is similar for each forest type, but rare bird species are confined to the virgin forest remnant. The biological differences between the two types of forest have led to changes in the physical site conditions. The results of the research are valuable in assessing the consequences of near‐to‐nature forest management.