Woodland Birds Research Articles

Optimal restoration of altered habitats

We describe a new conservation decision support tool: ‘Optimal Restoration of Altered Habitats’ (OPRAH). OPRAH combines species landscape configuration preferences and habitat quality information to optimally select habitat restoration priorities for single or multiple species. OPRAH uses a simulated annealing algorithm and information about extant native vegetation, land use and rehabilitation costs, to find solutions to non-linear landscape-scale problems. The landscape is divided into planning units, some of which represent native vegetation, while others can be restored for a given budget. A habitat restoration problem for declining woodland bird species is demonstrated as a case study.

What makes an effective restoration planting for woodland birds?

Large-scale vegetation clearing accompanying agricultural development has been a major driver of biodiversity loss. Efforts to reverse this problem have often included revegetation, but the value of revegetated areas for biodiversity is poorly known. We addressed aspects of this knowledge gap using a case study in south-eastern Australia. We quantified relationships between bird species richness and the probability of detection for eight individual bird species and: (i) the context of a planting, i.e. the types of the vegetation cover in the neighborhood of a planting, (ii) the configuration of a planting, i.e. the location and geometry of a planting, and, (iii) the content of planting, i.e. the vegetation features of a planting. The presence and nature of the effects of these explanatory variables varied with each of our response variables. A combination of context, configuration and content variables were needed to explain the variability in species richness and the presence of individual species. Context effects were highly significant, particularly the amount of planted and remnant native vegetation surrounding plantings. We speculate that when the area surrounding a planting was potentially suitable, recognition of planting “patch” boundaries disappeared and, correspondingly, configuration effects such as planting size were limited. Our results suggest that maximizing the value of planted areas for bird biota requires consideration not only of the features of the vegetation within a planting, but also where a planting is placed.

Extinction debt or habitat change? – Ongoing losses of woodland birds in north-eastern New South Wales, Australia

The loss, fragmentation and degradation of native vegetation are major causes of loss of biodiversity globally. Extinction debt is the term used to describe the ongoing loss of species from fragmented landscapes long after the original loss and fragmentation of habitat. However, losses may also result from habitat changes that are unrelated to fragmentation, which reduce breeding success and recruitment. Many woodland birds have declined in fragmented landscapes in Australia, probably due to loss of small, isolated populations, though the ecological processes are poorly understood. We record the progressive regional loss of two ground-foraging, woodland birds, the Brown Treecreeper Climacteris picumnus and Hooded Robin Melanodryas cucullata, in northern New South Wales, over 30 years. This has happened despite most habitat loss occurring over 100 years ago, suggesting the payment of an extinction debt. Our observations suggest that several ecological processes, caused by habitat loss, fragmentation or degradation, and operating over different time scales, have led to both species’ declines. Female Brown Treecreepers disperse poorly among vegetation remnants, leaving only males in isolated populations, which then go extinct. In contrast, Hooded Robins suffer high nest predation in fragmented landscapes, producing too few recruits to replace adult mortality. Foraging by both species may also be affected by regrowth of ground vegetation and shrubs. We found little support for a major role played by drought, climate change or aggressive Noisy Miners Manorina melanocephala. We propose that both extinction debt in the classical sense and ongoing habitat change frequently contribute to species’ decline in modified landscapes. Management to arrest and reverse such declines needs to consider these multiple causes of decline. For instance, reconnecting isolated populations may be inadequate alone, and activities such as appropriate grazing, fires and the addition of woody debris may also be required.

Do Highly Modified Landscapes Favour Generalists at the Expense of Specialists? An Example using Woodland Birds

Demands on land use in heavily populated landscapes create mosaic structures where semi-natural habitat patches are generally small and dominated by edges. Small patches are also more exposed and thus more vulnerable to adverse weather and potential effects of climate change. These conditions may be less problematic for generalist species than for specialists. Using insectivorous woodland birds (great tits and blue tits) as an example, we demonstrate that even generalists suffer reduced breeding success (in particular, rearing fewer and poorer-quality young) and increased parental costs (daily energy expenditure) when living in such highly modified secondary habitats (small woods, parks, farmland). Within-habitat heterogeneity (using the example of Monks Wood NNR) is generally associated with greater species diversity, but to benefit from heterogeneity at a landscape scale may require both high mobility and the ability to thrive in small habitat patches. Modern landscapes, dominated by small, modified and scattered habitat patches, may fail to provide specialists, especially sedentary ones, with access to sufficient quantity and quality of resources, while simultaneously increasing the potential for competition from generalists.

Seasonality of Nectar Production by Woodland Plants on the Gove Peninsula

In this paper I report flowering periods and indices of nectar availability over two years, for seven common plants regarded as being important nectar resources for birds in savannah woodland and rehabilitated mined land on the Gove Peninsula. Nectar availability varied seasonally, being lowest from December to February and highest in June and October each year. Nectar availability differed significantly between years, the difference being predominantly attributable to eucalypts, which exhibited large inter-annual differences in flowering, in contrast to the more consistent flowering of non eucalypts. Fern-leaved Grevillea contributed most to the nectar index (30%) across study sites. Darwin Stringybark contributed 10% to the overall nectar index, although this is considered an underestimate of its importance to nectar availability on the Gove Peninsula. Although birds were observed feeding on the nectar of all plant species for which the nectar index was calculated, Fern-leaved Grevillea (8 bird species) and Darwin Woollybutt (7 bird species) attracted the largest variety of birds.

Continuum or discrete patch landscape models for savanna birds? Towards a pluralistic approach

Conceptualising landscapes as a mosaic of discrete habitat patches is fundamental to landscape ecology, metapopulation theory and conservation biology. An emerging question in ecology is: when is the discrete patch model more appropriate than alternative and conceptually appealing models such as the continuum model? There is limited empirical testing of the utility of alternative landscape models compared to the discrete patch model for a range of species. In this paper, we constructed three alternative sets of models for testing the effect of landscape structure on diversity and abundance of a suite of woodland birds in a savanna landscape of northern Australia: the null model (only site‐scale habitat variables, landscape context not important), the continuum model, and the discrete patch model. We utilised high‐spatial resolution satellite images to quantify spatial gradients in tree cover density (the continuum model), and to then aggregate the fine‐scale heterogeneity in tree cover into discrete patches of trees, with grass cover forming the “matrix” (the discrete patch‐model). We then evaluated the relative importance of the alternative models using generalised linear models and an information theoretic approach. We found that the importance of the models varied among species, with no single model dominant. Species that move between open grassy areas and woody shelter responded well to the continuum model, reflecting the importance of gradients in density of forage (grasses) and cover (trees), while the discrete model performed best for species that forage in all vegetation strata, and nest predominantly in dense woody vegetation. This finding supports a pluralistic approach, highlighting the need for adopting and testing more than one landscape model in savanna landscapes, and in other landscapes that do not have a well defined patch structure.

Potential impact of grey squirrels Sciurus carolinensis on woodland bird populations in England

Several woodland bird species have declined markedly in abundance in England over the past 40 years, whilst the grey squirrel Sciurus carolinensis, a non-native nest predator, has increased. Given the timing, there has been concern that grey squirrels have driven these declines, although there is little data to support this view. Using novel analytical methods and extensive national bird and grey squirrel monitoring data, we examine whether there is evidence that woodland bird populations in England have been depressed by grey squirrels and whether there is a relationship between nest failure and squirrel numbers. Our results indicate that grey squirrels are very unlikely to have driven observed declines of woodland birds in recent years, although the number of associations, positive as well as negative, between grey squirrels and woodland birds is greater than expected by chance. For this reason, we cannot exclude the possibility that the populations of a small number of bird species, principally increasing species, have been depressed to some degree at sites where a greater number of grey squirrels were present. Of these species, perhaps the most convincing evidence is for Common Blackbird Turdus merula and Eurasian Collared Dove Streptopelia decaocto where nest record data also identified a positive relationship between nest failure at the egg stage and squirrel abundance.

Factors affecting site occupancy by woodland bird species of conservation concern

Significant biodiversity loss is characteristic of agricultural landscapes worldwide. Biodiversity recovery efforts in such landscapes can be hamstrung by a paucity of information on factors affecting species’ distributions, particularly for threatened and/or declining species. The temperate woodlands of south-eastern Australia have been extensively modified for agriculture and numerous bird taxa are declining. We have explicitly identified habitat and landscape attributes of woodland remnants affecting site occupancy by 13 woodland bird species of conservation concern. Using case-control data and linear logistic regression, we found that site occupancy for each species was related to both habitat and landscape variables. Habitat variables of particular importance included those in the ground layer (an abundance of leaf litter, an intact surface crust of mosses and lichens and a scarcity of annual grasses) and overstorey (a scarcity of eucalypt dieback and an abundance of mistletoe). Landscape variables strongly affecting site occupancy included the number of paddock trees and the area of native grass within 500 m of a site. Many of our study species were found most often in regrowth remnants. Our findings indicate a gap between current conservation practices and the actual habitat requirements of woodland bird species of conservation concern. Successful management will require protection and/or rehabilitation of the ground layer and overstorey of woodland remnants and sympathetic management of the surrounding landscape. It also will require managers to go beyond current practices of conserving old growth remnants and establishing replantings to maintaining and creating stands of woodland regrowth.

Remote sensing and the future of landscape ecology

Landscape ecology focuses on the analysis of spatial pattern and its relationship to ecological processes. As a scientific discipline, landscape ecology has grown rapidly in recent years, supported by developments in GIS and spatial analysis techniques. Although remote sensing data are widely employed in landscape ecology research, their current and potential roles have not been evaluated critically. To provide an overview of current practice, 438 research papers published in the journal Landscape Ecology for the years 2004—2008 were examined for information about use of remote sensing. Results indicated that only 36% of studies explicitly mentioned remote sensing. Of those that did so, aerial photographs and Landsat satellite sensor images were most commonly used, accounting for 46% and 42% of studies, respectively. The predominant application of remote sensing data across these studies was for thematic mapping purposes. This suggests that landscape ecologists have been relatively slow to recognize the potential value of recent developments in remote sensing technologies and methods. The review also provided evidence of a frequent lack of key detail in studies recently published in Landscape Ecology , with 75% failing to provide any assessment of uncertainty or error relating to image classification and mapping. It is suggested that the role of remote sensing in landscape ecology might be strengthened by closer collaboration between researchers in the two disciplines, by greater integration of diverse remote sensing data with ecological data, and by increased recognition of the value of remote sensing beyond land-cover mapping and pattern description. This is illustrated by case studies drawn from Latin America (focusing on forest loss and fragmentation) and the UK (focusing on habitat quality for woodland birds). Such approaches might improve the analytical and theoretical rigour of landscape ecology, and be applied usefully to issues of outstanding societal interest, such as the impacts of environmental change on biodiversity and ecosystem services.

Regent Honeyeater Habitat Restoration Project Lurg Hills, Victoria

Summary The Regent Honeyeater Habitat Restoration Project is a landscape scale community effort to protect and restore all significant remnants of native woodland habitat in the agricultural district of the Lurg hills, Victoria. While focus is placed on the Regent Honeyeater, many other declining birds and mammals also benefit from the restoration project. Over 14 years of sustained effort, the project has involved 115 local landholders (approximately 95% of local farms) and about 17 000 volunteers. Together, they have protected relatively healthy remnants by fencing, planted or direct seeded depleted understoreys and replanted open areas that had been cleared for agriculture. Other restoration activities include ecological thinning of ‘pole forests’, mistletoe removal, environmental weeding, feral animal control, kangaroo reduction, systematic monitoring of a range of threatened and declining woodland birds, and nest box placement for hollow‐dependent mammals. The works have achieved the rapid closing of some high‐priority gaps in the local landscape, connecting the Lurg hills project area to other major regional habitats nearby. The oldest tree plantings are now 12 yrs old and 6‐m high and the first Ironbarks flowered in 2006. While the Regent Honeyeater has not yet returned in numbers (because the trees have not yet reached optimum flowering age), surveys and nest box monitoring reveal a range of threatened birds and mammals are already using this project’s regenerated and reconstructed habitats.

Population trends of breeding birds in British woodlands over a 32‐year period: relationships with food, habitat use and migratory behaviour

This paper outlines population trends (with confidence intervals) for 49 species in woodland habitats in Britain as monitored by the British Trust for Ornithology’s (BTO) Common Bird Census (CBC) between 1967 and 1999. Additionally, the possible causes of these population trends are investigated by relating the ecological characteristics of species to the degree of population change they have undergone over different time periods. Over the whole period, 17 species showed significant decreases in abundance and 12 species showed significant increases. Whilst population trajectories were diverse, long‐distance migrants showed more negative trends than other species and the timing of the changes in their populations was related to their wintering latitude, suggesting that these species may be suffering from environmental changes in the non‐breeding season. There was also support for habitat specializations being related to population changes, with species classified as scrub and understorey specialists declining on average, but this was only evident across the entire study period. Additionally, species eating seeds in summer declined and those eating vegetation and making use of the agricultural landscape matrix increased. Therefore wide‐scale factors such as landscape‐scale processes or processes operating outside of Britain appear to be important in addition to local habitat change, especially for long‐distance migrants.

Mapping forest patches and scattered trees from SPOT images and testing their ecological importance for woodland birds in a fragmented agricultural landscape

Scattered trees represent an important element within the agricultural matrix for birds. The aims of this study were to develop methods for mapping isolated trees from satellite imagery and to assess the importance of isolated trees for bird species richness. Field sampling of birds and plants was conducted at 120 sites in south-east Australia. We mapped tree cover from Landsat and SPOT images using a combination of spectral and segmentation based methods. Mapping of isolated trees as point objects was highly accurate (80–90%). Tree cover at spatial extents of 3–28 ha around sites explained 60% of the variability in woodland–dependent bird species richness. However, isolated trees in agricultural areas made just a small contribution to explaining the spatial variability in overall avian richness. This approach can be used for more extensive assessment of avian habitat quality from high spatial resolution images across a range of human modified landscapes.

Exurban development influences woodland bird composition

One of the fastest growing types of land-use change is exurban development—low-density housing outside urban service boundaries. However, how individual species are responding to exurban development remains uncertain. We monitored birds for 5 years across three housing density levels in northern California oak woodlands. We compared community and species responses to exurban development (4–16 ha parcels) with suburban and undeveloped natural areas. We found that individual species and groups of species exhibited variable responses to exurban development. Some species and guilds were impacted by exurban development to the same extent as suburban development while others were less sensitive to this type of land use. For example, the proportion of the bird community composed of tree-and-shrub feeders was similar between exurban and natural areas, whereas proportions of temperate migrants showed significant reductions at both suburban and exurban sites. Similarly, Northern Flicker, Hutton's Vireo, and Orange-crowned Warbler were equally rare in exurban and suburban sites, making large, undeveloped parcels essential for their conservation. By explicitly measuring ecological changes associated with parcel size and density this research provides valuable information to land-use planners on the consequences of zoning for biodiversity conservation.

Habitat preferences of the noisy miner (Manorina melanocephala) – a propensity for prime real estate?

AbstractThis study investigated habitat characteristics that have been postulated to influence the occurrence of noisy miners (Manorina melanocephala Family Meliphagidae). It builds on an earlier study that identified corners along remnant edges as important predictors of the presence of noisy miners in large blocks of remnant vegetation (>300 ha). Six habitat characteristics were recorded at 39 corner sites within the box‐ironbark region of Victoria. We failed to detect any significant effect of the density of understorey vegetation on the likelihood of noisy miners occupying a site, but this might have been an artefact of prolonged drought conditions. The most powerful predictors of the presence of noisy miners at remnant corners were found to be soil type and the proportion of canopy trees at a site that were yellow gum (Eucalyptus leucoxylon), with noisy miners being associated with deeper, more fertile soils and higher proportions of yellow gums present. As yellow gum is a prolific and reliable nectar producer, the inherent productivity of a site might be more important in determining the attractiveness of a site to noisy miners than structural attributes like the presence or absence of an understorey. Noisy miners are sedentary colonial birds that occupy year‐round territories, often at high densities. Sites capable of supporting such high density occupation year‐round might be limited to the most productive sites within the landscape. This productivity hypothesis has potentially profound implications for other woodland avifauna, as noisy miners might be excluding other woodland birds from some of the most fertile components of the landscape; components that are already rare in the box‐ironbark region due preferential clearing for agriculture at the time of settlement.

Nesting, foraging and aggression of Noisy Miners relative to road edges in an extensive Queensland forest

Increased abundance of Noisy Miners (Manorina melanocephala), a large, aggressive honeyeater, is one of the most important mechanisms through which habitat fragmentation and degradation threaten populations of eastern Australian woodland birds. In inland Queensland, however, Noisy Miners dominate avian assemblages throughout extensive forest areas as well as fragmented landscapes, and our understanding of the factors influencing their behaviour and habitat selection in such relatively intact landscapes is limited. I investigated how road edges influenced Noisy Miners by comparing the species’ aggressive and foraging behaviour, and location of nests, between road-edge and interior transects in a southern Queensland forest. I also investigated Noisy Miner foraging microhabitat preferences and targets of aggression. Noisy Miner nests were more likely to be located near to road edges, but foraging and aggressive interactions occurred with similar frequency near and far from road edges. Such interactions selectively targeted close competitors and a nest predator. Most foraging activity was in the canopy, and selectively within ironbarks (Eucalyptus spp.), suggesting that higher densities of Noisy Miners in more open areas of the forest are unlikely to be related to facilitation of ground-foraging activity. Despite some evidence of a preference for nesting near road openings, road edges do not appear to influence Noisy Miners as strongly as edges between forest and agricultural land do elsewhere in eastern Australia.

Hybrid poplar plantations in a floodplain have balanced impacts on farmland and woodland birds

Hybrid poplar plantations are increasing worldwide and are often accused of impoverishing bird communities. We conducted 124 bird point counts in a landscape where plantations, semi-natural forests and farmland occupied similar surface areas. As expected, birds occurred at higher densities in areas dominated by forests than dominated by plantations, mostly due to the scarcity of late-successional forest birds in plantations. Contrary to expectations, bird communities were the poorest in farmland dominated areas and the most specialised in areas dominated by young plantations. Indeed, many grassland species, including some of conservation concern in Europe, frequently used young plantations. However, plantations have probably depleted grassland bird communities by fragmenting open areas, while playing a limited positive role on forest species. Total length of unpaved roads had a positive effect on community specialisation index, while total length of paved roads and mean forest/plantation patch size played no role. Bird density increased with the development of the understory vegetation in mature poplar plantations. We conclude that poplar should not be planted at the expense of areas of high conservation value; in other cases, they may increase the overall diversity of bird communities. At the plantation scale, we advocate stopping understory removal as soon as possible and maintaining old trees and hedgerows alongside or within plantations to provide suitable breeding habitats for bird species that may be foraging in the plantations.

Distance to edges, edge contrast and landscape fragmentation: Interactions affecting farmland birds around forest plantations

Afforestation often causes direct habitat losses for farmland birds of conservation concern, but it is uncertain whether negative effects also extend significantly into adjacent open land. Information is thus required on how these species react to wooded edges, and how their responses are affected by edge and landscape characteristics. These issues were examined in Mediterranean arable farmland, using bird counts at 0, 100, 200, 300 and >300 m from oak, pine and eucalyptus edges, embedded in landscapes with variable amounts and spatial configurations of forest plantations. Bird diversity declined away from edges, including that of woodland, farmland and ground-nesting birds. Positive edge responses were also found for overall and woodland bird abundances, and for five of the nine most widespread and abundant species ( Galerida larks, stonechat, linnet, goldfinch and corn bunting). Strong negative edge effects were only recorded for steppe birds, with reduced abundances near edges of calandra larks and short-toed larks, but not of little bustards and tawny pipits. Edge contrast affected the magnitude of edge effects, with a tendency for stronger responses to old and tall eucalyptus plantations (hard edges) than to young and short oak plantations (soft edges). There were also species-specific interactions between edge and fragmentation effects, with positive edge responses tending to be strongest in less fragmented landscapes, whereas steppe birds tended to increase faster away from edges and to reach the highest species richness and abundances in large arable patches. Results suggest that forest plantations may increase overall bird diversity and abundance in adjacent farmland, at the expenses of steppe birds of conservation concern. Clustering forest plantations in a few large patches and thus reducing the density of wooded edges at the landscape-scale might reduce such negative impacts.

Sacrificing patches for linear habitat elements enhances metapopulation performance of woodland birds in fragmented landscapes

It is generally assumed that large patches of natural habitat are better for the survival of species than the same amount of habitat in smaller fragments or linear elements like hedges and tree rows. We use a spatially explicit individual-based model of a woodland bird to explore this hypothesis. We specifically ask whether mixtures of large, small and linear habitat elements are better for population performance than landscapes that consist of only large elements. With equal carrying capacity, metapopulations perform equally or better in heterogeneous landscape types that are a mix of linear, large and small habitat elements. We call this increased metapopulation performance of large and small elements “synergy”. These mixed conditions are superior because the small linear elements facilitate dispersal while patches secure the population in the long run because they have a lower extinction risk. The linear elements are able to catch and guide dispersing animals which results in higher connectivity between patches leading to higher metapopulation survival. Our results suggest that landscape designers should not always seek to conserve and create larger units but might better strive for more variable landscapes with mixtures of patch sizes and shapes. This is especially important when smaller units play a key role in connecting patches and dispersal through the matrix is poor.

The consistency and stability of abundance–occupancy relationships in large‐scale population dynamics

1. Abundance-occupancy relationships comprise some of the most general and well-explored patterns in macro-ecology. The theory governing these relationships predicts that species will exhibit a positive interspecific and intraspecific relationship between regional occupancy and local abundance. Abundance-occupancy relationships have important implications in using distributional surveys, such as atlases, to understand and document large-scale population dynamics and the consequences of environmental change. A basic need for interpreting such data bases is a better understanding of whether changes in regional occupancy reflect changes in local abundance across species of varying life-history characteristics. 2. Our objective was to test the predictions of the abundance-occupancy rule using two independent data sets, the New York State Breeding Bird Atlas and the North American Breeding Bird Survey. The New York State Breeding Bird Atlas consists of 5332 25-km(2) survey blocks and is one of the first atlases in the USA to be completed for two time periods (1980-85 and 2000-05). The North American Breeding Survey is a large-scale annual survey intended to document the relative abundance and population change of songbirds throughout the USA. 3. We found that regional occupancy was positively correlated with relative abundance across 98 (beta = 0.60 +/- 0.11 SE, P < 0.001, R(2) = 0.60) and 85 species (beta = 0.67 +/- 0.06 SE, P < 0.001, R(2) = 0.57) in two separate time periods. This relationship proved stable over time and was notably consistent between breeding habitat groups and migratory guilds. 4. Between 1980 and 2005, changes in regional occupancy were highly correlated with long-term abundance trend estimates for 75 species (beta = 5.73 +/- 0.24 SE, P < 0.001, R(2) = 0.88). Over a 20-year period, woodland and resident birds showed an increase in occupancy while grassland species showed the greatest decline; these patterns were mirrored by changes in local abundance. 5. Although exceptions existed, we found most changes in occupancy parallel changes in local abundance. These findings support the basic predictions of the abundance-occupancy rule and demonstrate its consistency and stability in species and groups of varying life-history characteristics.

Population Trends of Breeding Birds on the Edwards Plateau, Texas: Local Versus Regional Patterns

I compared population trends of 32 species of shrubland and woodland birds generated from 10 years (1995–2004) of point counts on Fort Hood Military Reservation, Texas, with trend data for the same species and time period generated by the Breeding Bird Survey for the entire Edwards Plateau region of Texas. Regardless of scale, most (>90%) species exhibited acceptable population trajectories (i.e., stable or increasing trends). Trend directions were the same at local and regional scales for the majority (62.5%) of species despite differences in land use and management at local and regional scales. Most trend differences were attributable to stable populations on Fort Hood while populations increased on the Edwards Plateau, or vice versa. Stable or increasing population trends for most of the species I examined likely are related to continued or increased availability of woody habitat. Only two species, ladder-backed woodpecker (Picoides scalaris) and field sparrow (Spizella pusilla), exhibited declines at the regional level, possibly due to afforestation or development, which may be cause for concern. Because the population status of many of the species that use woody habitats on the Edwards Plateau appear to be acceptable, greater research and management emphasis should be placed on grassland birds, a group that has experienced substantial declines on the Edwards Plateau and nationally.