Stuart E. Newson

Winter availability of cereal stubbles attracts declining farmland birds and positively influences breeding population trends

Many studies have demonstrated the selection of stubble fields by farmland birds in winter, but none have shown whether provisioning of this key habitat positively influences national population trends for widespread farmland birds. We use two complementary extensive bird surveys undertaken at the same localities in summer and winter and show that the area of stubble in winter attracts increased numbers of several bird species of conservation concern. Moreover, for several farmland specialists, the availability of stubble fields in winter positively influenced the 10 year breeding population trend (1994–2003) whereas hedgerow bird species were less affected. For skylarks and yellowhammers, initially negative trends showed recovery with 10–20 ha of stubble per 1 km square. Thus, agri-environment schemes that promote retention of over-winter stubbles will attract birds locally and are capable of reversing current population declines if stubbles are available in sufficient quantity.

Evaluating the Breeding Bird Survey for producing national population size and density estimates

Capsule The BBS has potential for producing better estimates of habitat-specific densities and population sizes for many UK bird populations than those available previously. Aims To examine the use of the Breeding Bird Survey (BBS) in providing unbiased national population and habitat-specific density estimates of British birds. Methods Line transect data collected by volunteers in 1998 from 2287 1-km squares across the UK were analysed using distance sampling methods to calculate habitat-specific density and abundance estimates. For each species, the habitat-specific decline in detectability with distance from a transect line was modelled and applied at a regional level to incorporate variation in sampling intensity in different areas of the country. Results National population and density estimates calculated here were at a magnitude expected for at least seven species in this study. However, national population size estimates were higher than expected for Starling Sturnus vulgaris, House Sparrow Passer domesticus, Blackbird Turdus merula, Greenfinch Carduelis chloris, Jackdaw Corvus monedula, Whitethroat Sylvia communis, Woodpigeon Columba palumbus and Linnet Carduelis cannabina and lower than expected for Skylark Alauda arvensis, Dunnock Prunella modularis, Song Thrush Turdus philomelos and Corn Bunting Miliaria calandra. These differences are likely to be related to differences in sampling design and survey methods. For example, Starling, House Sparrow, Blackbird, Jackdaw, Greenfinch and Wood Pigeon, which have considerable populations in urban areas, were undoubtedly underestimated by the Common Birds Census (CBC). The counts of species that flock during the breeding season, or are not strongly territorial (e.g. Linnet, Jackdaw and Wood Pigeon) could be biased if detectability is strongly related to flock size. National population estimates of Skylark and Corn Bunting are lower than those based on CBC, but higher, or similar, to targeted national surveys of these species. Possible reasons for the differences between these estimates are considered. Conclusions This study highlights the strength of the BBS over previous data sources in producing national estimates of density and abundance at the habitat and national level. More research on the sex ratio and status of birds counted during surveys, and on the reliability of the detectability functions derived from distance sampling is needed to improve the interpretation of population estimates derived from BBS data.

Modelling population changes using data from different surveys: the Common Birds Census and the Breeding Bird Survey

Capsule A method for producing and validating long-term population indices using data from the Common Birds Census and its successor, the Breeding Bird Survey, is described. Aim To investigate a means of combining site-specific records from two very different surveys into reliable population indices. Methods A generalized linear model is described for Common Birds Census (CBC) and Breeding Bird Survey (BBS) data, and used to identify species and geographical regions for which the resulting temporal trends are comparable, and hence derive long-term trends that straddle the overlap of the two surveys. Results From 1994 to 2000, when both the CBC and the BBS were in operation, no significant difference in population trends in southeastern Britain between the two surveys was detected for the vast majority of the 73 species considered. CBC data are limited outside this region, but an analysis of BBS data over the same period showed that the trends outside this region were significantly different for around half of the species considered. Conclusion Although the predominant means of gathering data on terrestrial breeding birds has changed since the 1960s, a joint analysis of the combined data from the surveys can be used to produce annual indices of abundance for most species with sufficient data for either the whole or at least a proportion of Britain.

Developing and enhancing biodiversity monitoring programmes: a collaborative assessment of priorities

Summary Biodiversity is changing at unprecedented rates, and it is increasingly important that these changes are quantified through monitoring programmes. Previous recommendations for developing or enhancing these programmes focus either on the end goals, that is the intended use of the data, or on how these goals are achieved, for example through volunteer involvement in citizen science, but not both. These recommendations are rarely prioritized. We used a collaborative approach, involving 52 experts in biodiversity monitoring in the UK, to develop a list of attributes of relevance to any biodiversity monitoring programme and to order these attributes by their priority. We also ranked the attributes according to their importance in monitoring biodiversity in the UK. Experts involved included data users, funders, programme organizers and participants in data collection. They covered expertise in a wide range of taxa. We developed a final list of 25 attributes of biodiversity monitoring schemes, ordered from the most elemental (those essential for monitoring schemes; e.g. articulate the objectives and gain sufficient participants) to the most aspirational (e.g. electronic data capture in the field, reporting change annually). This ordered list is a practical framework which can be used to support the development of monitoring programmes. Peoples ranking of attributes revealed a difference between those who considered attributes with benefits to end users to be most important (e.g. people from governmental organizations) and those who considered attributes with greatest benefit to participants to be most important (e.g. people involved with volunteer biological recording schemes). This reveals a distinction between focussing on aims and the pragmatism in achieving those aims. Synthesis and applications. The ordered list of attributes developed in this study will assist in prioritizing resources to develop biodiversity monitoring programmes (including citizen science). The potential conflict between end users of data and participants in data collection that we discovered should be addressed by involving the diversity of stakeholders at all stages of programme development. This will maximize the chance of successfully achieving the goals of biodiversity monitoring programmes.

Comparison of habitat‐specific trends in the abundance of breeding birds in the UK

Capsule Trends in the relative abundance of 18 out of 23 breeding bird species of conservation concern varied significantly between habitats. Aims To produce and compare habitat‐specific trends in abundance of widespread breeding birds of conservation concern in the UK. Methods Breeding Bird Survey data for 23 red‐ and amber‐listed species were compared across 12 habitat categories. Habitat preference indices were calculated for each species and population trends were compared between favoured and avoided habitats, with the expectation that declines would be greatest in avoided, assumed poorer‐quality, habitats (the buffer effect). Results Over 75% of species showed significant variation in trends in abundance across habitats. In some species the annual rate of change differed by more than 10% between habitats. There was no consistent relationship between the trend of a species within a habitat and its preference index for that habitat. Conclusions The rate at which species of conservation concern are changing in abundance varies between habitats. Some species are declining more quickly in preferred habitats, others in avoided habitats, showing little consistent support for the buffer effect. Habitat‐specific trends should be considered when deciding how best to focus conservation efforts.

Should we account for detectability in population trends

Capsule Accounting for changes in detectability over time which could invalidate population trends for common and widespread breeding birds in the UK, resulted in little change in trends for the majority of species considered. Aims To examine whether detectability has a significant influence on population trends for common and widespread breeding birds in the UK. Methods Using data collected over 16 years of the UK Breeding Bird Survey (1994–2009) and focusing on a random sample of 20 common and widespread bird species, we examine the extent to which controlling for temporal change in detectability would influence national population trends. Results Population trends were significantly different for only 2 of the 20 species, Common Blackbird and Winter Wren. This difference corresponds to an apparent fall off in detectability of these species between 2005 and 2009. For the remaining species, controlling for detectability resulted in no significant difference in population trends. Conclusions The importance of detectability should be examined as part of any long-term monitoring programme. However, currently we do not find sufficient support for routinely incorporating detectability into population trends for widespread and abundant breeding birds in the UK.

Mapping from heterogeneous biodiversity monitoring data sources

Field monitoring can vary from simple volunteer opportunistic observations to professional standardised monitoring surveys, leading to a trade-off between data quality and data collection costs. Such variability in data quality may result in biased predictions obtained from species distribution models (SDMs). We aimed to identify the limitations of different monitoring data sources for developing species distribution maps and to evaluate their potential for spatial data integration in a conservation context. Using Maxent, SDMs were generated from three different bird data sources in Catalonia, which differ in the degree of standardisation and available sample size. In addition, an alternative approach for modelling species distributions was applied, which combined the three data sources at a large spatial scale, but then downscaling to the required resolution. Finally, SDM predictions were used to identify species richness and high quality areas (hotspots) from different treatments. Models were evaluated by using high quality Atlas information. We show that both sample size and survey methodology used to collect the data are important in delivering robust information on species distributions. Models based on standardized monitoring provided higher accuracy with a lower sample size, especially when modelling common species. Accuracy of models from opportunistic observations substantially increased when modelling uncommon species, giving similar accuracy to a more standardized survey. Although downscaling data through a SDM approach appears to be a useful tool in cases of data shortage or low data quality and heterogeneity, it will tend to overestimate species distributions. In order to identify distributions of species, data with different quality may be appropriate. However, to identify biodiversity hotspots high quality information is needed.

Species traits explain variation in detectability of UK birds

Capsule Heterogeneous detectability amongst species may impact multi-species bird surveys and if not accounted for, may bias community level conclusions. Estimates of detectability were produced for 195 UK bird species, and detectability was significantly affected by bird size, diet and habitat specialization. Aims To estimate detectability and understand which species traits may impact detectability. Methods We estimated the detectability of 195 species of birds in the UK using distance sampling methods and examined the average detectability of genetically related groups. We tested the significance of species traits in describing variation in detectability, whilst controlling for phylogenetic relationships. Results Passeriformes had the lowest median detectability of 0.37 and Charadriiformes the highest median detectability of 0.65, of the seven largest orders considered. Species most associated with closed habitats such as woodland and urban areas had the lowest detectability. Smaller species had lower detectability than larger species. Conclusion Heterogeneity in species detectability could lead to biased conclusions, particularly when calculating multi-species indices such as species richness or diversity. Accounting for detectability will be most important in studies that cover a wide range of habitat types or a diverse spread of taxa.

Fine-tuning the assessment of large-scale temporal trends in biodiversity using the example of British breeding birds

Summary The current headline indicator for ecosystem health and sustainability incorporates a geometric mean of relative abundances of breeding birds. Recently, a family of diversity measures (λ-measures) has been proposed as a novel instrument to separate diversity trends in dominant and rare species. This makes them an ecologically informative complement to current composite diversity indices. Using both a geometric mean and the set of λ-measures, we study habitat-specific temporal trends in the diversity of British breeding birds. The analysis employs abundance estimates corrected for variation in detectability between individuals from different species to reduce bias. Applying generalized additive models, we predict long-term trends. We locate significant changes in these diversity trends. While the geometric mean reveals overall diversity trends by habitat type, supplementing these by the λ-measures provides a more nuanced picture of trends: a positive trend in the geometric mean may hide predominantly declining trends among the rarer species, which is then revealed by trends in the λ-measures. Synthesis and Applications. Bird populations are seen as useful indicators of the health of wildlife and the countryside because they occupy a range of habitats, they tend to be towards the top of the food chain, and data is provided by long-term surveys. Hence, many countries apply wild bird indicators (WBIs), quantifying trends in biodiversity, to monitor environmental health. The UKs WBI, for example, has become one of the governments headline indicators of sustainable development. Understanding the population changes underlying the estimated trends is indispensable if we are to allocate limited resources more effectively. Employing a novel set of measures alongside the traditional geometric mean index, we analyse diversity trends among British breeding birds. It reveals that species that are scarce, but not yet in the focus of conservation action, may be the ‘losers’ in biodiversity action plans. This suggests that additional resources should be devoted to species showing long-term decline before they reach the low population levels that currently trigger large-scale species-specific rescue projects.

Potential for coupling the monitoring of bush-crickets with established large-scale acoustic monitoring of bats

Summary Monitoring biodiversity over large spatial and temporal scales is crucial for assessing the impact of global changes and environmental mitigation measures. However, large-scale monitoring of invertebrates remains poorly developed despite the importance of these organisms in ecosystem functioning. Exciting possibilities applicable to professional and citizen science are offered by new recording techniques and methods of semi-automated species recognition based on sound detection. Static broad-spectrum detectors deployed to record throughout whole nights have been recommended for standardised acoustic monitoring of bats, but they have the potential to also collect acoustic data for other species groups. Large-scale deployment of such systems is only viable when combined with robust automated species identification algorithms. Here we examine the potential of such a system for detecting, identifying and monitoring bush-crickets (Orthoptera of the family Tettigoniidae). We use incidental sound recordings generated by an extensive citizen science bat survey and recordings from intensive site surveys to test a semi-automated step-wise method with a classifier for assigning species identities. We assess species’ diel activity patterns to make recommendations for survey timing and interpretation of existing nocturnal data sets and consider the feasibility of determining site occupancy. Of six species of bush-crickets, the species classifier achieved over 85% accuracy for three, speckled bush-cricket, dark bush-cricket and Roesels bush-cricket. It should be possible to automatically scan recordings for these species with minimal manual validation. Further refinement of the classifier is required for the three remaining species, in particular for the acoustically similar short-winged conehead and long-winged conehead. Diel activity patterns are species specific and it may be necessary to adjust the hours over which the detectors record to increase detection of key species, but this must be weighed against the costs in terms of increased memory and battery use and equipment security during daytime. We conclude that with logistical support and centralised semi-automated species identification it is now possible for the public to contribute to large-scale acoustic monitoring of Orthoptera while recording bats. Further innovation of sound classifier algorithms is needed and would be aided by improved reference sound libraries from multiple locations spanning species’ ranges.