Site vegetation characteristics are more important than landscape context in determining bird assemblages in revegetation

The effectiveness of revegetation in providing habitat for fauna is expected to be determined both by within‐site factors and attributes of the landscape in which a revegetation site occurs. Most studies of fauna in revegetation have been conducted in landscapes that have been extensively cleared, modified or fragmented, and in Australia, predominantly in the southern temperate zone. We investigated how within‐site vegetation attributes and landscape context attributes were related to bird species richness and composition in a chronosequence of post‐mining rehabilitation sites within an otherwise intact landscape in tropical northern Australia. Our working hypothesis was that bird species richness in rehabilitating sites would be positively related to site vegetation structure and landscape context including (1) proximity to woodland and (2) the proportion of woodland within a 500‐m buffer of rehabilitation sites. Within each of 67 sites, we sampled vegetation once and surveyed for birds eight times over 16 months. Landscape context variables were calculated using GIS. There were large differences between bird assemblages of woodland and rehabilitation sites and between age classes of rehabilitation. Bird assemblages were strongly related to site vegetation attributes across all rehabilitation sites. Proximity to woodland was only related to bird assemblages in rehabilitation sites older than 4 years old. We conclude that the relative importance of landscape context and site variables at any point in time will be a function of how closely vegetation within the revegetation site matches the habitat resource requirements of individual species.     

Are predators negative or positive predictors of farmland bird species community on a large geographical scale?

Species distribution models (SDMs) are numerical tools that combine species occurrence/density or species richness with environmental data in order to predict particular species’ distribution. In most cases only abiotic environmental parameters are used as predictors, while biotic interactions which control distribution of species and influence the goodness of fit of the SDM, such as predator–prey systems, have been broadly neglected. For this reason, we tested the usefulness of easy to detect predators, such as the Common Buzzard and the Common Raven, as positive and negative predictors, respectively, of farmland bird species richness. We analyzed factors affecting the density of both predators and farmland bird species using data from 958 1 × 1 km² study plots in Poland and a set of 22 environmental variables. Next, we also included these predators’ densities as additional predictors of farmland bird species. Habitat and climatological predictors were aggregated using the Principal Components Analysis and then related to the Common Raven's and the Common Buzzard's densities as well as farmland bird species richness using General Additive Models. Finally, completed models were assessed according to information – theoretic criteria. Our results showed that all the analyzed groups occurred in open areas; the Common Buzzard and passerine bird species preferred traditional farmland, while the Common Raven reached its highest density in modern intensive farmland. Importantly, we documented a significant increase in the goodness of fit of SDMs for farmland bird species, having added the density of predators as negative (Common Raven) and positive (Common Buzzard) predictors. Consequently, our findings suggest that species’ specific models can improve the predictive power of SDMs and can be used as an effective tool for predicting bird diversity with higher accuracy.     

Habitat selection of breeding riparian birds in an urban environment: untangling the relative importance of biophysical elements and spatial scale

Aim Urbanization is a leading threat to global biodiversity, yet little is known about how the spatial arrangement and composition of biophysical elements – buildings and vegetation – within a metropolitan area influence habitat selection. Here, we ask: what is the relative importance of the structure and composition of these elements on bird species across multiple spatial scales? Location The temperate metropolitan area of Cincinnati, Ohio, USA. Methods We surveyed breeding birds on 71 plots along an urban gradient. We modelled relative density for 48 bird species in relation to local woody vegetation composition and structure and to tree cover, grass cover and building density within 50–1000 m of each plot. We used an information‐theoretic approach to compare models and variables. Results At the proximate scale, native tree and understory stem frequency were the most important vegetation variables explaining bird distributions. Species’ responses to landscape biophysical features and spatial scales varied. Most native species responded positively to vegetation measures and negatively to building density. Models combining both local vegetation and landscape information represented best or competitive models for the majority of species, while models containing only local vegetation characteristics were rarely competitive. Smaller spatial scales (≤ 500 m) were most important for 36 species, and eight species had best models at larger scales (> 500 m); however, several species had competitive models across multiple scales. Main conclusions Habitat selection by birds within the urban matrix is the result of a combination of factors operating at both proximate and broader spatial scales. Efforts to manage and design urban areas to benefit native birds require both fine‐scale (e.g., individual landowners and landscape design) and larger landscape actions (e.g., regional comprehensive planning).     

The spatial distribution of birds and carabid beetles in pine plantation forests: the role of landscape composition and structure

Aim To evaluate the joint and independent effects of spatial location, landscape composition and landscape structure on the distribution patterns of bird and carabid beetle assemblages in a mosaic landscape dominated by pine plantation forests. Location A continuous 3000‐ha landscape mosaic with native maritime pine Pinus pinaster plantations of different ages, deciduous woodlands and open habitats, located in the Landes de Gascogne forest of south‐western France. Methods We sampled breeding birds by 20‐min point counts and carabid beetles by pitfall trapping using a systematic grid sampling of 200 points every 400 m over the whole landscape. Explanatory variables were composed of three data sets derived from GIS habitat mapping: (1) spatial variables (polynomial terms of geographical coordinates of samples), (2) landscape composition as the percentage cover of the six main habitats, and (3) landscape structure metrics including indices of fragmentation and spatial heterogeneity. We used canonical correspondence analysis with variance partitioning to evaluate the joint and independent effects of the three sets of variables on the ordination of species assemblages. Moran's I correlograms and Mantel tests were used to assess for spatial structure in species distribution and relationships with separate landscape attributes. Results Landscape composition was the main factor explaining the distribution patterns of birds and carabids at the mesoscale of 400 × 400 m. Independent effects of spatial variables and landscape structure were still significant for bird assemblages once landscape composition was controlled for, but not for carabid assemblages. Spatial distributions of birds and carabids were primarily influenced by the amount of heathlands, young pine plantations, herbaceous firebreaks and deciduous woodlands. Deciduous woodland species had positive responses to edge density, while open habitat species were positively associated with mean patch area. Main conclusions Forest birds were favoured by an increase in deciduous woodland cover and landscape heterogeneity, but there was no evidence for a similar effect on carabid beetles. Fragmentation of open habitats negatively affected both early‐successional birds and carabids, specialist species being restricted to large heathlands and young plantations. Several birds of conservation concern were associated with mosaics of woodlands and grasslands, especially meadows and firebreaks. Conserving biodiversity in mosaic plantation landscapes could be achieved by the maintenance of a significant amount of early‐successional habitats and deciduous woodland patches within a conifer plantation matrix.     

Landscape structure influences tree density patterns in fragmented woodlands in semi‐arid eastern Australia

Landscape and local‐scale influences are important drivers of plant community structure. However, their relative contribution and the degree to which they interact remain unclear. We quantified the extent to which landscape structure, within‐patch habitat and their confounding effects determine post‐clearing tree densities and composition in agricultural landscapes in eastern subtropical Australia. Landscape structure (incorporating habitat fragmentation and loss) and within‐patch (site) features were quantified for 60 remnant patches of Eucalyptus populnea (Myrtaceae) woodland. Tree density and species for three ecological maturity classes (regeneration, early maturity, late maturity) and local site features were assessed in one 100 × 10 m plot per patch. All but one landscape characteristic was determined within a 1.3‐km radius of plots; Euclidean nearest neighbour distance was measured inside a 5‐km radius. Variation in tree density and composition for each maturity class was partitioned into independent landscape, independent site and joint effects of landscape and site features using redundancy analysis. Independent site effects explained more variation in regeneration density and composition than pure landscape effects; significant predictors were the proportion of early and late maturity trees at a site, rainfall and the associated interaction. Conversely, landscape structure explained greater variation in early and late maturity tree density and composition than site predictors. Area of remnant native vegetation within a landscape and patch characteristics (area, shape, edge contrast) were significant predictors of early maturity tree density. However, 31% of the explained variation in early mature tree differences represented confounding influences of landscape and local variables. We suggest that within‐patch characteristics are important in influencing semi‐arid woodland tree regeneration. However, independent and confounding effects of landscape structure resulting from previous vegetation clearing may have exerted a greater historical influence on older cohorts and should be accounted for when examining woodland dynamics across a broader range of environments.     

Local extinctions and recolonisations of passerine bird populations in small woods

This paper considers, for eight species of woodland bird, the factors that influenced both local extinctions and recolonisations in 145 woods over 3 years. In all species, probability of local extinction was inversely related to population size; most local extinctions occurred in woods containing one to three breeding pairs. However, considerable variation in extinction probabilities occurred between species and between years. In addition, the suitability of habitat within a wood (more extinctions in less suitable woods) was important for wren Troglodytes troglodytes, song thrush Turdus philomelos and blue tit Parus caeruleus; also, the structure of the surrounding landscape was important for blue tit, great tit Parus major, and chaffinch Fringilla coelebs (more extinctions in localities with less woodland). In only two species was the probability of recolonisation related to any of the measured variables. Wrens were more likely to recolonise larger woods, whereas song thrushes were more likely to recolonise woods with a high habitat suitability rating and those which are more isolated from other woodland     

Does landscape structure affect resource tracking by avian frugivores in a fragmented Afrotropical forest?

Frugivorous species heavily depend on patchy food resources and are believed to track these in space and time, thereby providing an important seed dispersal function that might be critical toward the regeneration of fruiting plants. However, isolation of suitable food patches due to habitat fragmentation or changes in landscape connectivity may hamper food tracking behaviour and adversely affect populations of both frugivores (through starvation) and food plants (through interruption of seed dispersal). We here test whether density fluctuations in four frugivorous Afrotropical bird species were larger and/or matched fluctuations in ripe fruit densities better in study plots embedded in large tracts of indigenous forest than in equally-sized plots embedded in cultivated lands. We compared these results with those of four non-frugivorous species (out-group) which were not expected to track fruit resources. Whereas densities of both frugivores and fruit crops strongly fluctuated in space and time, these fluctuations were not synchronised, nor did the level of synchrony differ in relation to matrix type. For some but not all bird species, lower densities and smaller temporal fluctuations in forest plots surrounded by cultivation may reflect decreased mobility. The observed fluctuations in bird densities most likely reflect exchange with the surrounding landscape matrix, suggesting that small pockets of fruiting trees in farmland may comprise critical food resources for frugivores inhabiting highly fragmented landscapes, apart from increasing connectivity for both bird and seed dispersal.     

Synchrony of woodland bird populations: the effect of landscape structure

The influence of environmental stochasticity and dispersal in producing patterns in population synchrony was examined for 53 woods censused annually from 1990 to 1999 for nine resident bird species (wren Troglodytes troglodytes , dunnock Prunella modularis , robin Erithacus rubecula , blackbird Turdus merula , song thrush Turdus philomelos , long-tailed tit Aegithalos caudatus , blue tit Parus caeruleus , great tit Parus major , and chaffinch Fringilla coelebs ) and four migrant bird species (garden warbler Sylvia borin , blackcap Sylvia atricapilla , chiffchaff Phylloscopus collybita and willow warbler Phylloscopus trochilus ). Twelve species showed global synchrony of population counts due to regional population trends and widespread annual population fluctuations. There was a clear link between population fluctuations and winter weather for wren, and three other species showed their largest population declines after the coldest winters. Eight species showed a decline in synchrony with distance between woods, and there was evidence for dispersal causing this pattern in three species. Landscape structure affected patterns of synchrony in several species, with lower synchrony in landscapes with less woodland. For three species, this difference in synchrony across a landscape gradient of decreasing woodland cover accounted for the decline in synchrony over distance. Three species showed greater synchrony between woods with similar amounts of hedgerow in the surrounding landscape, suggesting that the surroundings of a wood influence the population dynamics of some species breeding in the wood. Habitat fragmentation can alter the processes contributing to population synchrony. Loss of woodland reduces the relative abundance of woodland bird species. The remaining patches of habitat are smaller, more isolated and are set in a more hostile landscape, all of which may disrupt dispersal between patches and alter the population dynamics within woods.     

How much abandoned farmland is required to harbor comparable species richness and abundance of bird communities in wetland? Hierarchical community model suggests the importance of habitat structure and landscape context

While wetlands have been converted into farmlands, large amounts of farmlands are now being abandoned, and this novel habitat is expected to be inhabited by species which depend on wetlands. Here we examined the effects of habitat and landscape variables on the densities of wetland bird species in abandoned farmlands. We surveyed birds in abandoned farmlands with different patch area, habitat, and landscape variables in Kushiro district, eastern Hokkaido, northern Japan. We also surveyed birds in 15 ha of the remaining wetlands as a reference habitat. We used abundance-based hierarchical community models (HCMs) to estimate patch-level estimates of abundance of each species based on sampling plots data that only partially covered the studied patches. We observed 14 wetland species and analyzed them with HCMs. Abandoned farmland patch areas had significant positive effects on the densities of two species. Tree densities and shrub coverage exerted positive and negative effects on some species. Amounts of surrounding wetland/grassland had positive effects on many species. Ensemble of species-level models suggested that 24.7 and 10.6 ha of abandoned farmlands would be needed to harbor a comparable total abundance and species richness in 15-ha wetlands, respectively. These required amounts can be increased/decreased depending on the covariates. The use of HCMs allows us to predict species- and community-level responses under varied conditions based on incomplete sampling data. A quantity of 1.6 times larger areas of abandoned farmlands may be required to restore wetland bird communities in eastern Hokkaido.     

潜在洞巢资源差异对次级洞巢鸟及繁殖鸟类群落的影响

为了解次生林中潜在洞巢资源(包括各种啄木鸟的啄洞和人工巢箱)的多寡对次级洞巢鸟集团及繁殖鸟类群落结构的影响, 2007年11月至2008年7月, 我们在吉林省吉林市大岗林场选择洞巢密度不同的样地, 对其次级洞巢鸟及鸟类群落结构进行了比较研究。根据洞巢资源密度我们将9块样地分为3组, 即巢箱区(啄洞密度最低, 悬挂人工巢箱使其潜在洞巢资源总密度大幅提高)、低密度区(啄洞密度较低, 无巢箱)和高密度区(啄洞密度较高, 无巢箱), 调查了3组样地内鸟类的组成和密度、潜在洞巢资源的利用情况等。3组样地中均调查到4种初级洞巢鸟, 其种类组成略有不同; 4种次级洞巢鸟在3组样地广泛分布, 分别为白眉姬鹟(Ficedula zanthopygia)、大山雀(Parus major)、沼泽山雀(P. palustris)和普通鳾(Sitta europaea)。巢箱区和高密度区的次级洞巢鸟总密度显著高于低密度区。巢箱区同高密度区一样, 大山雀和白眉姬鹟的密度显著高于低密度区, 这是由于大山雀和白眉姬鹟是人工巢箱的主要利用鸟种, 而沼泽山雀和普通鳾的密度在三组样地间差异不显著。初级洞巢鸟总密度与啄洞密度、次级洞巢鸟总密度与潜在洞巢资源总密度都呈显著正相关关系。潜在洞巢资源丰富的样地中鸟类群落多样性指数显著高于潜在洞巢资源贫乏样地中的鸟类群落多样性指数, 人为增加洞巢资源可以改变鸟类群落组成并显著提高群落的多样性指数。三组样地中鸟类群落的均匀性、丰富度指数和种间相遇率没有显著差异, 群落相似性指数也相近。高密度区和低密度区鸟类群落集团结构相似。次级洞巢鸟密度的增加短时期内未对群落内其他主要鸟种的密度产生显著影响。研究结果显示, 初级洞巢鸟的密度决定了啄洞的丰富程度, 而洞巢资源的差异会对次级洞巢鸟集团的分布模式产生影响, 进而影响整个繁殖鸟类群落的结构。     

Bird Community Composition in a Shaded Coffee Agro-ecological Matrix in Puebla,Mexico: The Effects of Landscape Heterogeneity at Multiple Spatial Scales

This study examined the importance of habitat heterogeneity on the avian community composition, and investigated the scale at which species abundances respond to habitat variables. The study was conducted within a diverse landscape matrix of a shaded coffee region in Mexico. To detect at which characteristic spatial scale different species and foraging guilds respond most strongly we analyzed the effect of plot-, patch- and landscape-level variables at different spatial extent (i.e., different kilometer radii) on species composition and foraging guilds. We used redundancy analysis to identify species–environment correlations, and to identify predictor variables that best explained the bird community structure, quantified the influence of plot-, patch- and landscape-level variables on the bird community composition. In addition, we used the 4th-corner method to detect significant relationships between the dietary guilds and plot-, patch- and landscape-level variables. We recorded 12,335 individuals of 181 bird species; 105 bird species were recorded foraging within the shaded coffee plantations. We found that plot- and landscape-level variables significantly explained the bird community composition best across all scales, and were significantly correlated with the abundance of the dietary guilds. In contrast, patch-level variables were less important. Habitat composition variables (i.e., coffee, forest and agricultural area) were among the most important predictors. Canopy structure was more important than other vegetation structure variables in explaining dietary guild structure. Hence, the maintenance of a heterogeneous landscape with a high-quality matrix within an agro-ecological region enhances bird conservation.     

Pasture area and landscape heterogeneity are key determinants of bird diversity in intensively managed farmland

Agriculture intensification has drastically altered farmland mosaics, while semi-natural grasslands have been considerably reduced and fragmented. Bird declines in northern temperate latitudes are attributed to habitat loss and degradation in farmed landscapes. Conversely, landscape-modification effects on grassland/farmland bird communities are less studied in the South American temperate grasslands. We investigated how bird communities were influenced by landscape characteristics in the Rolling Pampa (Argentina). We sampled bird communities in 356 landscapes of 1-km radius that varied in cover and configuration of pastureland, flooding grassland and cropland. Using generalized linear models, we explored the relationship between both bird species richness and abundance, and landscape structure. Analyses were carried out for all species, and open-habitat, grassland and aquatic species. Pasture area was far the most important factor, followed by landscape composition, in predicting species richness and abundance, irrespective of specific habitat preferences, followed by partially-flooded grassland cover and its mean shape index. Grassland fragmentation did not affect species richness or abundance. When comparing the effects of landscape variables on bird richness and abundance (using mean model coefficients), pasture and grassland area effects were on average more than four times greater than those of compositional heterogeneity, and about ten times greater than shape effects. To conserve species-rich bird communities persisting in Rolling Pampa farmland, we recommend the preservation of pasture and grassland habitats, irrespective of their fragmentation level, in intensively managed farmland mosaics.     

Testing indicators of sustainable forest management on understorey composition and diversity in southern Italy through variation partitioning

Tree species composition and stand structural complexity are valuable indicators of sustainable forest management. This article aims to investigate the relative influence of forest overstorey composition and structural attributes on understorey composition and diversity, taking into account also site characteristics and broad-scale environmental variables. We sampled vascular plant species composition and forest structure in 132 plots in the Cilento and Vallo di Diano National Park (southern Italy). Spearman’s non-parametric correlation coefficients were calculated between overstorey and understorey diversity indices, beech percentage, and altitude and environmental indices. A complete partitioning of the variation in understorey composition was then performed through canonical correspondence analysis considering four sets of variables: (1) overstorey composition, (2) structural attributes, (3) topography, and (4) landscape abiotic variables. Finally, we constructed a regression tree analysis of understorey species richness using the same explanatory variables. Understorey diversity indices were positively correlated with overstorey diversity indices and with environmental indices (i.e., light and soil heterogeneity). Overstorey and understorey diversity indices were negatively correlated with both altitude and the dominance of beech in the overstorey. Compositional variation was due primarily to overstorey composition and secondarily to structural attributes. Regression tree analysis revealed that altitude, overstorey species richness, and structural attributes play an important role in determining understorey species richness. According to our results, understorey composition and diversity are strongly related to overstorey composition and structural attributes. Indeed, the latter proved to be effective indicators of understorey characteristics in the study area.     

Estimating breeding season abundance of golden-cheeked warblers in Texas,USA

Population abundance estimates using predictive models are important for describing habitat use and responses to population-level impacts, evaluating conservation status of a species, and for establishing monitoring programs. The golden-cheeked warbler (Setophaga chrysoparia) is a neotropical migratory bird that was listed as federally endangered in 1990 because of threats related to loss and fragmentation of its woodland habitat. Since listing, abundance estimates for the species have mainly relied on localized population studies on public lands and qualitative-based methods. Our goal was to estimate breeding population size of male warblers using a predictive model based on metrics for patches of woodland habitat throughout the species' breeding range. We first conducted occupancy surveys to determine range-wide distribution. We then conducted standard point-count surveys on a subset of the initial sampling locations to estimate density of males. Mean observed patch-specific density was 0.23 males/ha (95% CI = 0.197–0.252, n = 301). We modeled the relationship between patch-specific density of males and woodland patch characteristics (size and landscape composition) and predicted patch occupancy. The probability of patch occupancy, derived from a model that used patch size and landscape composition as predictor variables while addressing effects of spatial relatedness, best predicted patch-specific density. We predicted patch-specific densities as a function of occupancy probability and estimated abundance of male warblers across 63,616 woodland patches accounting for 1.678 million ha of potential warbler habitat. Using a Monte Carlo simulation, our approach yielded a range-wide male warbler population estimate of 263,339 (95% CI: 223,927–302,620). Our results provide the first abundance estimate using habitat and count data from a sampling design focused on range-wide inference. Managers can use the resulting model as a tool to support conservation planning and guide recovery efforts. © 2012 The Wildlife Society.     

Woody elements benefit bird diversity to a larger extent than semi-natural grasslands in cereal-dominated landscapes

Increasing landscape complexity can mitigate negative effects of agricultural intensification on biodiversity by offering resources complementary to those provided in arable fields. In particular, grazed semi-natural grasslands and woody elements support farmland birds, but little is known about their relative effects on bird diversity and community composition. In addition, the relative importance of local habitat versus landscape composition remains unclear. We investigated how the presence of semi-natural grasslands, the number of woody elements and the composition of the wider agricultural landscape affect bird species richness, true diversity (exponential Shannon diversity) and species composition. Bird communities were surveyed four times on 16 paired transects of 250 m each with 8 transects placed between a crop field and a semi-natural grassland and 8 transects between two crop fields with no semi-natural grasslands in the vicinity. The number of woody elements around transects was selected as an important predictor in all models, having a positive effect on species richness and true diversity, while the local presence of semi-natural grasslands was not selected in the best models. However, species richness and true diversity increased with increasing cover of ley and semi-natural grasslands, whereas species composition was modified by the coverage of winter wheat at the landscape scale. Furthermore, bird species richness, true diversity and species composition differed between sampling dates. As bird diversity benefited from woody elements, rather than from the local presence of semi-natural grasslands as such, it is important to maintain woody structures in farmland. However, the positive effect of grassland at the landscape scale highlights the importance of habitat variability at multiple scales. Because species richness and true diversity were affected by different landscape components compared to species composition, a mosaic of land-use types is needed to achieve multiple conservation goals across agricultural landscapes.     

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.     

Combined effects of landscape composition and heterogeneity on farmland avian diversity

Conserving biodiversity on farmland is an essential element of worldwide efforts for reversing the global biodiversity decline. Common approaches involve improving the natural component of the landscape by increasing the amount of natural and seminatural habitats (e.g., hedgerows, woodlots, and ponds) or improving the production component of the landscape by increasing the amount of biodiversity‐friendly crops. Because these approaches may negatively impact on economic output, it was suggested that an alternative might be to enhance the diversity (compositional heterogeneity) or the spatial complexity (configurational heterogeneity) of land cover types, without necessarily changing composition. Here, we develop a case study to evaluate these ideas, examining whether managing landscape composition or heterogeneity, or both, would be required to achieve conservation benefits on avian diversity in open Mediterranean farmland. We surveyed birds in farmland landscapes of southern Portugal, before (1995–1997) and after (2010–2012) the European Union's Common Agricultural Policy (CAP) reform of 2003, and related spatial and temporal variation in bird species richness to variables describing the composition, and the compositional and configurational heterogeneity, of the natural and production components of the landscape. We found that the composition of the production component had the strongest effects on avian diversity, with a particularly marked effect on the richness of farmland and steppe bird species. Composition of the natural component was also influential, mainly affecting the richness of woodland/shrubland species. Although there were some effects of compositional and configurational heterogeneity, these were much weaker and inconsistent than those of landscape composition. Overall, we suggest that conservation efforts in our area should focus primarily on the composition of the production component, by striving to maximize the prevalence of biodiversity‐friendly crops. This recommendation probably applies to other areas such as ours, where a range of species of conservation concern is strongly associated with crop habitats.     

Effects of landscape composition on farmland and red-listed birds in boreal agricultural-forest mosaics

Farmland birds have declined in large areas of western and northern Europe. This decline has been connected with changes in the agricultural landscape. We studied the effects of landscape composition on birds in a boreal agricultural-forest mosaic in SW Finland. This study was carried out with a grid-based approach: bird pairs were counted in 105 grid squares of 25 ha within an area of 26.25 km². The total density of farmland birds and density of red-listed species were related to the land cover variables using generalized linear modelling (GLM). Farmland birds consist of a variable group of species either breeding or feeding in agricultural land. The model explained a moderate proportion (49%) of the variation in the total density of farmland birds in the landscape. In a regression analysis cover of non-arable agricultural land (semi-natural grasslands, built-up areas) explained a much higher proportion (r²=0.49) of the variation in farmland bird density than that of arable land (cultivated fields and set-aside fields, r²=0.04). Semi-natural grasslands, which have drastically declined throughout NW Europe, and built-up areas (mainly farmyards) had the most significant positive effects on the density of red-listed species. The results emphasize the significance of semi-natural grasslands for the declining red-listed farmland bird species. Birds are usually not restricted to certain patches of habitat but use several patches in their home range. Thus, when studying bird-landscape relations for land use planning, we also recommend grid-based approaches covering the whole landscape variation.     

Heterospecific attraction and food resources in migrants' breeding patch selection in northern boreal forest

We studied experimentally how heterospecific attraction may affect habitat selection of migrant passerine birds in Finnish Lapland. We manipulated the densities of resident tit species (Parus spp.). In four study plots residents were removed before the arrival of the migrants in the first study year, and in four other plots their densities were increased by releasing caught individuals. In the second year the treatments of the areas were reversed, allowing paired comparisons within each plot. We also investigated the relative abundance of arthropods in the study plots by the sweep-net method. This allowed us to estimate the effect of food resources on the abundance of birds. The heterospecific attraction hypothesis predicts that densities of migrant species (especially habitat generalists) would be higher during increased resident density. Results supported this prediction. Densities and number of the most abundant migrant species were significantly higher when resident density was increased than when they were removed. On the species level the redwing (Turdus iliacus) showed the strongest positive response to the increased abundance of tits. Migrant bird abundances seemed not to vary in parallel with relative arthropod abundance, with the exception of the pied flycatcher (Ficedula hypoleuca) which showed a strongly positive correlation with many arthropod groups. The results of the experiment indicate that migrants can use resident tit species as a cue to a profitable breeding patch. The relationship between the abundance of the birds and arthropods suggests that annual changes in food resources during the breeding season probably do not have a very important effect on bird populations in these areas. The results stress the importance of positive interspecific interactions in structuring northern breeding bird communities. Received: 1 September 1997 / Accepted: 22 January 1998