David G. Noble

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.

Horizon scanning for invasive alien species with the potential to threaten biodiversity in Great Britain

Invasive alien species (IAS) are considered one of the greatest threats to biodiversity, particularly through their interactions with other drivers of change. Horizon scanning, the systematic examination of future potential threats and opportunities, leading to prioritization of IAS threats is seen as an essential component of IAS management. Our aim was to consider IAS that were likely to impact on native biodiversity but were not yet established in the wild in Great Britain. To achieve this, we developed an approach which coupled consensus methods (which have previously been used for collaboratively identifying priorities in other contexts) with rapid risk assessment. The process involved two distinct phases: Preliminary consultation with experts within five groups (plants, terrestrial invertebrates, freshwater invertebrates, vertebrates and marine species) to derive ranked lists of potential IAS. Consensus-building across expert groups to compile and rank the entire list of potential IAS. Five hundred and ninety-one species not native to Great Britain were considered. Ninety-three of these species were agreed to constitute at least a medium risk (based on score and consensus) with respect to them arriving, establishing and posing a threat to native biodiversity. The quagga mussel, Dreissena rostriformis bugensis, received maximum scores for risk of arrival, establishment and impact; following discussions the unanimous consensus was to rank it in the top position. A further 29 species were considered to constitute a high risk and were grouped according to their ranked risk. The remaining 63 species were considered as medium risk, and included in an unranked long list. The information collated through this novel extension of the consensus method for horizon scanning provides evidence for underpinning and prioritizing management both for the species and, perhaps more importantly, their pathways of arrival. Although our study focused on Great Britain, we suggest that the methods adopted are applicable globally.

Consistent response of bird populations to climate change on two continents.

Birds populations allied in abundance Changes in climate can cause populations of species to decline, to increase, or to remain steady. Stephens et al. looked across species of common birds in Europe and the United States. Despite many differences between the two regions, expectations about how a species might respond to climate change did predict actual responses. Species predicted to benefit from increasing temperatures, or their associated effects, tended to increase, whereas those predicted to be negatively affected declined. Thus, even across widely varying ecological conditions and communities, climate change can be expected to alter population sizes. Science, this issue p. 84 The impact of climate change on population sizes of birds across continents can be predicted. Global climate change is a major threat to biodiversity. Large-scale analyses have generally focused on the impacts of climate change on the geographic ranges of species and on phenology, the timing of ecological phenomena. We used long-term monitoring of the abundance of breeding birds across Europe and the United States to produce, for both regions, composite population indices for two groups of species: those for which climate suitability has been either improving or declining since 1980. The ratio of these composite indices, the climate impact indicator (CII), reflects the divergent fates of species favored or disadvantaged by climate change. The trend in CII is positive and similar in the two regions. On both continents, interspecific and spatial variation in population abundance trends are well predicted by climate suitability trends.

The generation and use of bird population indicators in Europe

Global and regional targets to reduce the rate of biodiversity loss bring with them the need to measure the state of nature and how it is changing. A number of different biodiversity indicators have been developed in response and here we consider bird population indicators in Europe. Birds are often used as surrogates for other elements of biodiversity because they are so well known and well studied, and not for their unique intrinsic value as environmental indicators. Yet, in certain situations and at particular scales, trends in bird populations correlate with those of other taxa making them a valuable biodiversity indicator with appropriate caveats. In this paper, we look at two case studies, in the UK and Europe as a whole, where headline bird indicators, that is, summary statistics based on bird population trends, have been developed and used to inform and assist policy makers. Wild bird indicators have been adopted by many European countries and by the European Union as indicators of biodiversity and of sustainable development. In the discussion, we review the strengths and weaknesses of using bird populations in this way, and look forward to how this work might be developed and expanded.

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.

Distributions of Habitat Suitability and the Abundance‐Occupancy Relationship

Positive abundance‐occupancy relationships (a relationship between the number of sites a species occupies and the average density of individuals in occupied sites) are widespread through a range of taxa. The simplest model for this is the “vital rates” model, which proposes that habitat suitability varies spatially; increasing average habitat quality thus leads to simultaneous increases in average densities within occupied areas, as well as the total area that is habitable. This model has not been tested. We develop a general analytical version of this model and show that it predicts that the skewness of population size or aggregation of individuals within sites should vary systematically with density and occupancy, depending on the distribution of habitat suitability, and that the variance in occupancy should be highest at low densities. We compare these predictions with data from the British Trust for Ornithology’s Common Birds Census, and we find systematic changes in both variance and skewness of density, both intra‐ and interspecifically.

Rarity, life history and scaling of the dynamics in time and space of British birds

1. Many patterns in macroecology are closely related to the total abundance of a species in a region. Here we show that interspecific differences in the pattern of population fluctuations of British bird species can be predicted from knowledge of their overall abundance and some basic life-history characteristics. 2. We identify a rarity syndrome that arises through an increased stochastic influence on population fluctuations with decreasing population size, mainly resulting from an inverse density-dependent effect of demographic stochasticity. This syndrome involves an increase in the annual changes in population size with increasing rarity in the United Kingdom. 3. The relationship between the magnitude of temporal variation and local mean population size differs between species dependent on their life history, i.e. species with larger clutch size and lower survival tended to have larger annual changes in population size than low-reproducing long-lived species. 4. The probability of local disappearance from a study plot depended on the population size and was hence closely related to the overall abundance of the species in UK. For a given population size, this probability was also related to species-specific life-history characteristics, being higher in species with larger clutch sizes and smaller survival rates. 5. Rareness results in a spatial decoupling of the temporal variation in population size. 6. These patterns show that once a species has become rare, e.g. due to human activities, key population dynamical characteristics will change because of density-dependent stochastic effects, which in turn are dependent on species-specific life-history characteristics.

GB Non-native Species Information Portal: documenting the arrival of non-native species in Britain

Abstract Information on non-native species (NNS) is often scattered among a multitude of sources, such as regional and national databases, peer-reviewed and grey literature, unpublished research projects, institutional datasets and with taxonomic experts. Here we report on the development of a database designed for the collation of information in Britain. The project involved working with volunteer experts to populate a database of NNS (hereafter called “the species register”). Each species occupies a row within the database with information on aspects of the species’ biology such as environment (marine, freshwater, terrestrial etc.), functional type (predator, parasite etc.), habitats occupied in the invaded range (using EUNIS classification), invasion pathways, establishment status in Britain and impacts. The information is delivered through the Great Britain Non-Native Species Information Portal hosted by the Non-Native Species Secretariat. By the end of 2011 there were 1958 established NNS in Britain. There has been a dramatic increase over time in the rate of NNS arriving in Britain and those becoming established. The majority of established NNS are higher plants (1,376 species). Insects are the next most numerous group (344 species) followed by non-insect invertebrates (158 species), vertebrates (50 species), algae (24 species) and lower plants (6 species). Inventories of NNS are seen as an essential tool in the management of biological invasions. The use of such lists is diverse and far-reaching. However, the increasing number of new arrivals highlights both the dynamic nature of invasions and the importance of updating NNS inventories.

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.