Woodland Birds Research Articles

Association between avian assemblages and mountain bushveld communities along a single mountain slope in the Usuthu Gorge, South Africa

The study investigated the bird species diversity associated with vegetation communities found on a single mountain slope in the Usuthu Gorge Community Conservation Area, northern KwaZulu-Natal. Thirteen sample sites were surveyed on a monthly basis for 12 months. Over this period, 279 birds and 55 species were recorded, of which the Dark-capped Bulbul Pycnonotus tricolor was the most abundant. The Rattling Cisticola Cisticola chiniana was the indicator species in the highest community, Open Bushveld, which is characterised by grassland and bush patches. The White-bellied Sunbird Cinnyris talatala was an indicator in the second-lowest community, Dense Bushveld–Woodland, which is characterised by steep slopes and thickets. In Wooded Grassland, located between the above two communities, the highest beta diversity (species turnover) was recorded and this outcome was probably caused by large areas covered by rocks that compelled woodland birds to move through this community. Contrary to expectation, the gamma diversity per vegetation community increased with elevation from 18 to 33 species in Dense Bushveld–Woodland, Wooded Grassland and Open Bushveld. A future study should measure bird species diversity on larger elevational gradients, i.e. slopes from 500 to 3 000 m above sea level, which also include more distinct vegetation communities.

Assessing the Natura 2000 network with a common breeding birds survey

Natura 2000 (N2000) is a network of European sites focused on the conservation of specific species and habitats. Despite the known importance of common biodiversity in ecosystem functioning, common species are currently not explicitly targeted by conservation initiatives in France. In this study, we investigated whether the N2000 network contributes to the protection of common breeding bird species. In particular, we focused on species abundance and species specialization, community specialization and community trophic levels. We also determined the effects of N2000 on temporal trends of specialist and generalist bird groups. We studied 100 species in 1461 plots monitored by the French Breeding Bird Survey (BBS) between 2001 and 2010. We found that species abundance increased for 54 species with the proportion of the plot covered by N2000 areas in the plot. The bird species with the abundances that were most influenced by proportion of the plot covered by N2000 areas were predominantly habitat specialists. Bird communities inside N2000 sites were more specialized and exhibited higher trophic indices than communities outside N2000 sites. We found no differences in the temporal trends of farmland and woodland birds inside and outside N2000 sites, but the temporal trend of generalist species was positive outside N2000 sites and stable inside. We concluded that N2000 sites showed greater abundance of a majority of common bird species but that the network was established too recently to assess its influence on population trends. The French BBS has proved to be an efficient tool in assessing protected area networks.

Using habitat extent and composition to predict the occurrence of woodland birds in fragmented landscapes

The removal, alteration and fragmentation of habitat are key causes of biodiversity decline worldwide. In Australia, temperate woodlands have been disproportionately cleared following European settlement. Biodiversity decline in such systems may be reversed by restoration of native vegetation on agricultural land. However, rebuilding functioning habitat will require understanding the determinants of species distributions in existing habitat. We used logistic regression of bird occurrence data from 240 sites across northern Victoria, to determine the probability of occurrence of 29 woodland-dependent bird species. We modelled occurrence as a function of habitat variables that characterise both the extent (amount) and composition of native vegetation surrounding sites. Our specific goal was to determine whether the predictive performance of models is improved by accounting for both extent and composition of native vegetation compared with models that characterise native vegetation by extent alone. For nearly all species, accounting for vegetation composition in addition to extent and weighting habitat variables by distance improved the explanatory power of models, explaining on average 5.4 % (range 0–27.6 %) of the residual uncertainty in models that accounted for extent alone. Models that incorporate variation in vegetation composition can not only provide more accurate predictions of species occurrence, but also guide more appropriate restoration. They highlight the need for restoration to incorporate sites with fertile soils that support productive vegetation types. These models of woodland birds will be used to inform a spatially-explicit optimisation model for restoring native vegetation cover on agricultural land in this region, with the goal of achieving biodiversity gains while minimizing loss to production.

Do woodland birds prefer to forage in healthy Eucalyptus wandoo trees?

Globally, many forests and woodlands are in decline. The marked loss of canopy foliage typical of these declines results in reduced foraging resources (e.g. nectar, pollen, and insects) and, subsequently, can reduce habitat quality for woodland birds. In south-west Western Australia, patches of Eucalyptus wandoo woodlands have shown a decline in condition since at least 2002. We investigated how changes in E. wandoo condition affect the woodland bird community. Foraging activities of three bird species were recorded for 20 sites in Dryandra State Forest and Wandoo Conservation Park either by conducting watches on focal trees (‘sitting’ method), or following individuals through the woodland (‘following’ method). Condition assessments of trees used by the birds were compared with those for trees available at the study site. Weebills (Smicrornis brevirostris; canopy insectivore) displayed preference for healthy trees (low amounts of canopy dieback), whereas rufous treecreepers (Climacteris rufa; bark-foraging insectivore) preferred trees with a higher proportion of dead branches. Yellow-plumed honeyeaters (Lichenostomus ornatus; insectivore/nectarivore) foraged in older, larger E. wandoo trees having full canopies with few signs of tree decline. Tree declines, such as that happening in E. wandoo, alter the foraging resources and habitat available to woodland birds.

Birds in remnant woodland vegetation in the central wheatbelt of New South Wales during the drought declared years 2005 to 2009

The woodlands of southern Australia have been extensively cleared for agriculture. The loss and fragmentation of the native vegetation has been followed by dramatic declines in woodland-dependant species. Here we present data from the Central Western Plains of New South Wales on the occurrence of birds in woodlands that have been highly fragmented and structurally altered over the last 150 years. The species composition of the region is still very similar to that recorded 3 decades earlier but many small insectivorous and nectivorous woodland birds are rare and restricted, while the woodland patches and remnant tree groves in the landscape are now dominated by the Galah, Noisy Miner, Australian Magpie, Crested Pigeon, Apostlebird, Magpie-lark, Grey-crowned Babbler, Australian Raven, Eastern Rosella and Pied Butcherbird.

Woodland birds persisting in least disturbed environment: Birds of Dryandra Woodland 1953–2008.

Woodland birds have seriously declined across southern Australian with local extinctions reported in many areas. Dryandra Woodland presents a contrasting picture to this decline with declining species persisting there. It retains an almost full community of birds, many of which have declined or disappeared from the surrounding wheatbelt. It is 27 000 ha of remnant woodland, situated ~160 km south-east of Perth, in south-western Australia. Birds were surveyed predominately by professional biologists and/or taken from their archives, publications and institutional databases for a 55 year period (173 observation years) from 1953 to 2008; 141 species were detected. Persistence rather than extinction and increase rather than decline were the dominant paradigms for the birds of Dryandra. This is the inverse of what has happened in the greater wheatbelt, in which Dryandra is located. It is postulated that Dryandra’s birds persist because their habitat is relatively unchanged compared to that of the surrounding wheatbelt. Despite the many ‘success stories’ some birds had declined, for example, Malleefowl Leipoa ocellata and Hooded Robin Melanodryas cucullata. Three species were judged to be locally extinct at Dryandra Spotted Nightjar Eurostopodus argus, Chestnut Quail-thrush Cinclosoma castanotum and Crested Bellbird Oreoica gutturalis.

The effect of patch area on birds in central Australian mulga (Acacia aneura) woodland of different times-since-fire.

It is often assumed that a fine-scaled mosaic of different times-since-fire supports greater biodiversity than a coarsescaled mosaic — the fire mosaic hypothesis. A potential mechanism of the fire mosaic hypothesis is the effect of area on species diversity. We investigated the effect of patch area on bird communities in mulga (Acacia aneura) woodland in central Australia. The study was conducted at Uluru Kata-Tjuta National Park using 55 fixed-area sites classified to the time since last fire: burnt 2002; burnt 1976 and long unburnt. Birds were surveyed in the winter and spring of 2005 and 2006. Of 20 key species, two showed a positive density-area effect (i.e. higher density in larger patches). Patch area did not affect total bird density or species richness. However, species turnover (ß-diversity) was greater in large patches in the burnt 2002 treatment than it was in small patches. There was no effect of patch area on the composition of the bird communities in any of the time-since-fire classes. We concluded that patch area did affect the distribution of some birds in mulga woodland. However, patch area was not a mechanism of the fire mosaic hypothesis because the effects of patch size tended to increase avian diversity in larger patches rather than small.

Relationships between patterns of habitat cover and the historical distribution of the Marsh Tit, Willow Tit and Lesser Spotted Woodpecker in Britain

Spatial analysis of remotely-sensed land cover data in conjunction with species distribution atlases can reveal large-scale relationships between animal taxa and their habitats. We investigated the historical distribution patterns of three declining woodland birds, the Marsh Tit (Poecile palustris), Willow Tit (Poecile montana) and Lesser Spotted Woodpecker (Dendrocopos minor), in relation to a parsimonious landscape metric for describing habitat availability in Britain. Bird distributions were derived from two field-based atlas surveys, conducted in 1968–1972 and 1988–1991, and used to classify areas of the landscape for each species as retained, lost or gained between atlas periods, or unoccupied in both. We used remotely-sensed land cover data from 1990 to compare percentage habitat cover between landscape areas classified by bird occupation, and regional summary data from national woodland inventories to investigate changes in habitat cover and bird distributions. Percentage habitat cover was a sufficient landscape metric to explain the distribution pattern of all three bird species; habitat cover was greatest in areas where each species was retained between atlas surveys, significantly less in areas from which species were lost, and least in areas that remained unoccupied. Reductions in Marsh Tit distribution were less in regions that showed greater increases in habitat cover, but there was no such relationship for other species. Results indicated that spatial studies could be used to infer aspects of the spatial ecology of species where field data is lacking: by comparing distribution patterns with the relatively well-studied Marsh Tit, we found support for the assumption that the Lesser Spotted Woodpecker occupies very large territories in Britain, and provided evidence that the spatial habitat requirements of the Marsh Tit could be used as a proxy for the data-poor Willow Tit. The results showed that the habitat cover required to retain each species in the landscape had increased over time, illustrating how spatial studies can be used to identify priorities for further research and suggest conservation measures for declining species, and these are discussed.

Contrasting effect of isolation of hedges from forests on farmland vs. woodland birds

Hedges and forest edges play a major role in providing nesting sites, food resources and shelter for birds in agricultural landscapes of western and central Europe. We investigated the response of farmland vs. woodland birds at two degrees of isolation of hedges from forest and to vegetation structure. We surveyed 200 m long sections of six forest edges, six hedges connected to forests and six isolated hedges. Species richness and abundance of farmland birds were higher in hedges than in forest edges, species richness and abundance of woodland birds were lower in hedges than in the forest edges. Species richness and abundance of both groups did not differ between connected and isolated hedges. Width and height of hedges and edges did not affect the species richness and abundance of either farmland or woodland birds. Furthermore, bird community composition differed between habitat types (hedge vs. forest edge) and also between hedge isolation levels (hedges connected to forest vs. isolated hedges). Based o...

Temporal consistency in fine-scale habitat relationships of woodland birds during a period of habitat deterioration

Temporal consistency of models of animal-habitat relationships is important because it is widely assumed that such models have long-term relevance for conservation management. Habitat associations can potentially shift over time due to changes in factors such as habitat quality, predation risk and intra-specific competition. Relationships between vegetation attributes and bird distribution were examined in rotationally harvested woodland in two breeding seasons separated by 16years. Over this period habitat suitability deteriorated for understory bird species as a result of increased browsing pressure by deer. Generalised additive models were constructed for eight species and three groups of songbirds (all species, migrants, hole-nesters), with choice of predictors and the assumed form of underlying relationships informed by cross-validation deviance. Three species differed strongly between years in their responses to age of vegetation regrowth following harvesting; in two of these cases the differences were probably a consequence of deer browsing altering relationships between age of regrowth and vegetation structure. Canopy height was generally the single best predictor and for six of the 11 response variables, height was the best predictor in both years. Density of shrub layer foliage was frequently the second best predictor in both years. Multi-variable models in most cases selected canopy height as the first variable. Floristic variables (i.e. ones measuring aspects of tree or shrub species composition) featured in 64% of the multi-variable models and 27% of the selected variables were floristic rather than structural. Overall, there was a high level of temporal consistency in the bird-habitat models with most species apparently keying into very similar vegetation structures irrespective of browsing pressure. Canopy height is considered to be a surrogate for a complex of micro-habitat elements associated with resource provision for many birds. However, the understory micro-structures that are important determinants of habitat quality for many forest species are difficult to measure in ecologically meaningful ways. New technologies potentially offer better ways of measuring these habitat attributes and of assessing how they are affected by forest management.

Little evidence that condition, stress indicators, sex ratio, or homozygosity are related to landscape or habitat attributes in declining woodland birds

Habitat loss, fragmentation and degradation are drivers of major declines in biodiversity and species extinctions. The actual causes of species population declines following habitat change are more difficult to discern and there is typically high covariation among the measures used to infer the causes of decline. The causes of decline may act directly on individual fitness and survival, or through disruption of population processes. We examined the relationships among configuration, extent and status of native vegetation and three commonly used indicators of individual body condition and chronic stress (haemoglobin level, haematocrit, residual body mass condition index) in 13 species of woodland‐dependent birds in south‐eastern Australia. We also examined two measures of changes to population processes (sex ratio and individual homozygosity) in ten species and alleic richness in five species. We found little support for relationships between site or landscape characteristics and individual or population response variables, notwithstanding that our simulations showed we had sufficient power to detect relatively small effects. We discuss possible causes of the absence of detectable habitat effects in this system and the implications for the usefulness of individual body condition and easily measured haematological indices as indicators of the response of avian populations to habitat change.

Describing Habitat Occupation by Woodland Birds with Territory Mapping and Remotely Sensed Data: An Example Using the Marsh Tit (Poecile palustris)

Abstract. Changes in the structure of woodlands and forests, caused by shifts in management, stand maturity, and composition, have been implicated in the population decline of some bird species in Europe and North America. One such species is the Marsh Tit (Poecile palustris). We investigated relationships between Marsh Tit occupation (derived from territory mapping) and vegetation structure, tree species composition, and proximity to woodland edge in a British woodland, using a combination of 5 years of occupation data and high-resolution (0.5 and 1 m), large-scale (155 ha) habitat models derived from remote sensing. The results demonstrated that Marsh Tit occupation was linked to vegetation characteristics through the woodland's full vertical profile and related significantly and positively with overstory height, tree canopy closure, and the coverage of understory vegetation below the overstory. Marsh Tit occupation was lower within 50 m of the woodland perimeter, where habitat structure was less favora...

Habitat selection and ranges of tolerance: how do species differ beyond critical thresholds?

Sensitivity to habitat fragmentation often has been examined in terms of thresholds in landscape composition at which a species is likely to occur. Observed thresholds often have been low or absent, however, leaving much unexplained about habitat selection beyond initial thresholds of occurrence, even for species with strong habitat preferences. We examined responses to varying amounts of tree cover, a widely influential measure of habitat loss, for 40 woodland bird species in a mixed woodland/grassland landscape in eastern North Dakota, USA. We used LOESS smoothing to describe incidence for each species at three scales: within 200, 400, and 1200 m around sample locations. For the 200-m scale, we also calculated the most-preferred range of tree cover (within which at least half of observations were predicted to occur) for each species. Only 10 of 40 species had occurrence thresholds greater than about 10% tree cover. After initial occurrence, species showed three general patterns: some increased monotonically with tree cover; some increased up to an asymptote; some peaked at intermediate amounts of tree cover and then declined. These patterns approximate selection for interior woodlands and for edge-rich environments, but incidence plots provide greater detail in landscape-scale selection than do those categories. For most species, patterns persisted at larger scales, but for some, larger scales had distinctly different patterns than local scales. Preferred ranges of tree cover varied from <20% tree cover (common grackle, Quiscalus quiscula) to >60% (veery, Catharus fuscescens). We conclude that incidence patterns provide more information on habitat selection than do threshold measures for most species: in particular, they differentiate species preferring concentrated woodlands from those preferring mixed landscapes, and they show contrasting degrees of selectiveness. [Correction added on 16 October 2012, after first online publication: the section has been reworded].

Declining woodland birds in North America: should we blame Bambi?

AbstractAimWe evaluate the possible link between increasing deer populations and declines in woodland birds.LocationNorth American continent.MethodsWe used a group of 73 forest bird species that had been tested for their sensitivity to the impact of overabundant deer on forest understory. We used Breeding Bird Survey data to assess population trends for these 73 songbird species between 1966 and 2009, a period of marked continent‐wide increases in white‐tailed (Odocoileus virginianus) and mule or black‐tailed (Odocoileus hemionus) deer.ResultsWe show a continent‐wide link between increase in deer populations and declines in forest–songbird species‐dependent on understory for nesting and/or foraging.Main conclusionsIncreasing deer populations may actually play an important and underestimated role in the decline of North American songbirds.

The importance of the surroundings: are bird communities of riparian galleries influenced by agroforestry matrices in SW Iberian Peninsula?

The remaining riparian stretches are often the unique suitable habitats for forest breeding birds in Mediterranean landscapes undergoing long-term changes. Understanding the interactions between riparian zones and their surroundings is critical to establish successful management actions. We assessed the influence of surrounding matrix on riparian bird communities and the use of riparian galleries as surrogate habitats for the forest passerine communities of southwestern Iberia. We used point counts in three simultaneous sampling stations, one in the riparian gallery and two in the adjacent matrix. Three matrix types were selected with a decreasing tree density gradient: dense montado, sparse montado, and open agricultural areas. Data were analysed with redundancy analysis and differences in species’ occurrences were tested with one-way ANOVA. In riparian galleries, we found bird species belong to three ecological guilds: riparian, woodland, and edge guilds. The richness of bird guilds and the occurrence of some species depended on the surrounding matrix type. Riparian bird richness was constant in all surrounding matrices, woodland bird guild was richer in galleries embedded in dense montados, and edge guild in riparian galleries surrounded by sparse montados. Five among 19 assessed species were influenced by matrix type, within particular a few strictly riparian species. Species richness increased close to riparian galleries, due to the increase in habitat heterogeneity and resource availability for birds in densely vegetated riversides. However, the occurrence of some bird species differed according to the type of surrounding matrix. The matrix type explained most of the variance in riparian bird assemblages. Some woodland birds have used riparian galleries as surrogate habitat. Our study suggests that land use in the surrounding matrices must be taking into account for the management and rehabilitation of watercourses and bird conservation actions.

Genes and song: genetic and social connections in fragmented habitat in a woodland bird with limited dispersal

Understanding the processes leading to population declines in fragmented landscapes is essential for successful conservation management. However, isolating the influence of disparate processes, and dispersal in particular, is challenging. The Grey Shrike-thrush, Colluricincla harmonica, is a sedentary woodland-dependent songbird, with learned vocalizations whose incidence in suitable habitat patches falls disproportionally with decline in tree cover in the landscape. Although it has been suggested that gaps in tree cover might act as barriers to its dispersal, the species remains in many remnants of native vegetation in agricultural landscapes, suggesting that it may have responded to habitat removal and fragmentation by maintaining or even increasing dispersal distances. We quantified population connectivity of the Grey Shrike-thrush in a system fragmented over more than 120 years using genetic (microsatellites) and acoustic (song types) data. First, we tested for population genetic and acoustic structure at regional and local scales in search of barriers to dispersal or gene flow and signals of local spatial structuring indicative of restricted dispersal or localized acoustic similarity. Then we tested for effects of habitat loss and fragmentation on genetic and acoustic connectivity by fitting alternative models of mobility (isolation-by-distance [the null model] and reduced and increased movement models) across treeless vs. treed areas. Birds within -5 km of each other had more similar genotypes and song types than those farther away, suggesting that dispersal and song matching are limited in the region. Despite restricted dispersal detected for females (but not males), populations appeared to be connected by gene flow and displayed some cultural (acoustic) connectivity across the region. Fragmentation did not appear to impact greatly the dispersal of the Grey Shrike-thrush: none of the mobility models fit the genetic distances of males, whereas for females, an isolation-by-distance model could not be rejected in favor of the models of reduced or increased movement through treeless gaps. However, dissimilarities of the song types were more consistent with the model of reduced cultural connectivity through treeless areas, suggesting that fragmentation impedes song type sharing in the Grey Shrike-thrush. Our paper demonstrates that habitat fragmentation hinders important population processes in an Australian woodland bird even though its dispersal is not detectably impacted.

What do declining woodland birds eat? A synthesis of dietary records

Ground-foraging insectivores are prominent among the 26 species considered ‘declining woodland birds’ in southern Australia but the mechanisms driving their declines remain elusive. Nutritional factors may be critical, with larger and more structurally complex woodlands supporting greater arthropod biomass, but these differences need not translate into more arthropods actually consumed by these insectivores. We synthesised existing dietary records of a subset of the 26 declining woodland birds—13 ground-foraging insectivorous passerines—to determine the range of arthropods consumed and to estimate the relative importance of each prey group for these birds. Declining insectivores consumed a wide array of arthropods, but diets were characteristically dominated by one or two prey groups: Coleoptera, Formicidae and Lepidoptera accounted for 58% of prey records. Coleoptera contributed the greatest proportion of records (27%) and was the dominant prey group in the diets of nine of the 13 birds. These popular prey groups likely represent core resources supporting populations of declining insectivores and measurement of their abundance may provide meaningful estimates of the availability of prey. We highlight the need to quantify the size-range and identity of those prey eaten by declining woodland birds, and propose that reliance on a small number of prey groups may underlie the sensitivity of ground-foraging insectivores to modification of habitat.

Wrong place, wrong time: climate change‐induced range shift across fragmented habitat causes maladaptation and declined population size in a modelled bird species

AbstractMany species are locally adapted to decreased habitat quality at their range margins, and therefore show genetic differences throughout their ranges. Under contemporary climate change, range shifts may affect evolutionary processes at the expanding range margin due to founder events. In addition, populations that are affected by such founder events will, in the course of time, become located in the range centre. Recent studies investigated evolutionary changes at the expanding range margin, but have not assessed eventual effects across the species' range. We explored the possible influence of range shift on the level of adaptation throughout the species' total range. For this we used a spatially explicit, individual‐based simulation model of a woodland bird, parameterized after the middle spotted woodpecker ( Dendrocopos medius) in fragmented habitat. We simulated its range under climate change, and incorporated genetic differences at a single locus that determined the individual's degree of adaptation to optimal temperature conditions. Generalist individuals had a large thermal tolerance, but relatively low overall fitness, whereas climate specialists had high fitness combined with a small thermal tolerance. In equilibrium, the populations in the range centre were comprised of the specialists, whereas the generalists dominated the margins. In contrast, under temperature increase, the generalist numbers increased at the expanding margin and eventually also occupied the centre of the shifting range, whereas the specialists were located in the retracting margins. This was caused by founder events and led to overall maladaptation of the species, which resulted in a reduced metapopulation size and thus impeded the species' persistence. We therefore found no evidence for a complementary effect of local adaptation and range shifts on species' survival. Instead, we showed that founder events can cause local maladaptation which can amplify throughout the species' range, and, as such, hamper the species' persistence under climate change.

Fine-scale effects of habitat loss and fragmentation despite large-scale gene flow for some regionally declining woodland bird species

Habitat loss and associated fragmentation effects are well-recognised threats to biodiversity. Loss of functional connectivity (mobility, gene flow and demographic continuity) could result in population decline in altered habitat, because smaller, isolated populations are more vulnerable to extinction. We tested whether substantial habitat reduction plus fragmentation is associated with reduced gene flow in three ‘decliner’ woodland-dependent bird species (eastern yellow robin, weebill and spotted pardalote) identified in earlier work to have declined disproportionately in heavily fragmented landscapes in the Box-Ironbark forest region in north-central Victoria, Australia. For these three decliners, and one ‘tolerant’ species (striated pardalote), we compared patterns of genetic diversity, relatedness, effective population size, sex-ratios and genic (allele frequency) differentiation among landscapes of different total tree cover, identified population subdivision at the regional scale, and explored fine-scale genotypic (individual-based genetic signature) structure. Unexpectedly high genetic connectivity across the study region was detected for ‘decliner’ and ‘tolerant’ species. Power analysis simulations suggest that moderate reductions in gene flow should have been detectable. However, there was evidence of local negative effects of reduced habitat extent and structural connectivity: slightly lower effective population sizes, lower genetic diversity, higher within-site relatedness and altered sex-ratios (for weebill and eastern yellow robin) in 10 × 10 km ‘landscapes’ with low vegetation cover. We conclude that reduced structural connectivity in the Box-Ironbark ecosystem may still allow sufficient gene flow to avoid the harmful effects of inbreeding in our study species. Although there may still be negative consequences of fragmentation for demographic connectivity, the high genetic connectivity of mobile bird species in this system suggests that reconnecting isolated habitat patches may be less important than increasing habitat extent and/or quality if these need to be traded off.

Predicting Landscape-Genetic Consequences of Habitat Loss, Fragmentation and Mobility for Multiple Species of Woodland Birds

Inference concerning the impact of habitat fragmentation on dispersal and gene flow is a key theme in landscape genetics. Recently, the ability of established approaches to identify reliably the differential effects of landscape structure (e.g. land-cover composition, remnant vegetation configuration and extent) on the mobility of organisms has been questioned. More explicit methods of predicting and testing for such effects must move beyond post hoc explanations for single landscapes and species. Here, we document a process for making a priori predictions, using existing spatial and ecological data and expert opinion, of the effects of landscape structure on genetic structure of multiple species across replicated landscape blocks. We compare the results of two common methods for estimating the influence of landscape structure on effective distance: least-cost path analysis and isolation-by-resistance. We present a series of alternative models of genetic connectivity in the study area, represented by different landscape resistance surfaces for calculating effective distance, and identify appropriate null models. The process is applied to ten species of sympatric woodland-dependant birds. For each species, we rank a priori the expectation of fit of genetic response to the models according to the expected response of birds to loss of structural connectivity and landscape-scale tree-cover. These rankings (our hypotheses) are presented for testing with empirical genetic data in a subsequent contribution. We propose that this replicated landscape, multi-species approach offers a robust method for identifying the likely effects of landscape fragmentation on dispersal.