Individual variation in reactions to novel aposematic prey is common in avian predators. In wild adults, this variation may be caused by differences among individuals in experience with various prey, but similar variation exists in naive juveniles, and this is linked to personality-a complex of correlated, partly heritable behavioral traits that are consistent across time. Along the extremes on an axis of early exploratory behavior in great tits (Parus major), fast explorers are bold, aggressive, and routine-forming, whereas slow explorers are shy, less aggressive, and more innovative. We tested the effect of personality on innate wariness toward aposematic prey in adult hand-reared great tits from 2 lines selected for opposite levels of early exploratory behavior (fast vs. slow). The birds were offered aposematic firebugs (Pyrrhocoris apterus) over 2 d. Birds from both selection lines showed a similar degree of innate wariness toward the firebugs on the first day, but on the second day, fast explorers approached the firebugs significantly faster and more frequently than slow birds. Whether the birds attacked the firebugs was also dependent on their personality. Thus, personality-related individual differences in reactions of great tits toward the aposematic prey were maintained in the adult life stage. Personality affects avian responses to aposematic prey. In great tits, fast explorers are bolder, slow explorers more cautious. We tested hand-reared adults from lines selected for fast versus slow exploration. Both fast and slow birds were initially wary of aposematic firebugs, but fast explorers approached and attacked firebugs more frequently in repeated test. Although adults were less likely to attack aposematic prey than juveniles tested in a previous study, personality-related differences were maintained over time.

The European Turtle-dove (Streptopelia turtur) has become a priority for conservation action, following decades of population decline.The 2018 Species Action Plan, agreed internationally, recommended regulating hunting through an adaptive harvest management mechanism (AHMM), an evidence-led system designed to facilitate decision making through continuous learning. The Turtle Dove AHMM was set up in 2020 overseen by the European Commission. In our role as scientific advisors to the AHMM, we used the PECBMS dataset to calculate flyway-specific estimates of key parameters that contribute to decision making: indices, trends and breeding population size variation over time, covering the periods 1998 – 2024 and 2000 – 2024. The persistent decline in both flyways, coupled with results from a population model based on demographic variables from the western flyway, supported the recommendation of a complete hunting ban from 2021 (western) and a 50% reduction (2021) followed by zero take from 2022 (central-eastern). PECBMS data allowed tracking the population response to such policy decisions. In the western flyway, numbers reached a historic low of 1.56 · 106 breeding pairs in 2021, then increased by 31.5% in the following three years, to 2.00 · 106 breeding pairs in 2024, i.e., 480 000 new breeding pairs. During this time, mean annual adult survival increased significantly, and is the most likely driver of the observed growth. In the central-eastern flyway, hunting effort was reduced but not eliminated, and the population maintained its overall decline. Numbers dropped to an all-time low of 0.56 · 106 breeding pairs in 2023, then increased non-significantly in 2024. Our study demonstrates the value of using the PECBMS dataset in conservation for the management of priority species. It further provides empirical evidence of the speed of population response in this quarry species, and the timeframe needed for change to occur and to be detected.

Multi-species indices (MSIs) are an important tool for monitoring progress towards conservation policy targets from the local to the global scale. The choice of constituent species for habitat-specific indicators often reflects context-specific knowledge, policy needs and data availability. This makes direct comparisons of equivalent indicators across various locations challenging, and potentially reduces their representativeness if subsequently applied to other locations or spatial scales. In recognition of this, there is growing demand to develop standardised approaches to species selection that produce more spatially comparable MSIs. Using forest bird species in Europe, we use an objective, niche-based framework for indicator species selection to derive standardised indices at national, regional and pan-European scales, and explore the implications for species composition on indicator trends when adopting three alternative species-selection strategies: selecting species representative of a given spatial scale (“geographically-targeted”), disaggregating a species set representative of a broad-scale for use at smaller scales (“top-down”) and aggregating species lists representative of smaller scales for use at larger scales (“bottom-up”). We show that although the composition of indicator sets varied according to the species’ selection approach, resultant index trends for a given location were generally comparable. However, “geographically-targeted” indicators tended to be comprised of more specialist species and were more representative of the wider community. Whilst existing biodiversity indices provide critical insights into the state of nature across spatial scales, our study provides the basis for the development of complementary, standardised indicators that are spatially comparable.

The population dynamics of urban animals has been so far remarkably understudied. At the same time, urban species’ population trends can provide important information on the consequences of environmental changes in cities. We modelled long-term population trends of 93 bird species breeding in urban areas in 16 European countries as a function of species’ traits, characterising variability in their urbanization and ecology. We found that: (i) earlier colonisers have more negative population trends than recent colonisers; (ii) more urbanized open habitat species had more positive population trends than less urbanized open habitat species; (iii) highly urbanized birds breeding above the ground had more negative trends than highly urbanized ground breeders. These patterns can be explained by several processes occurring in cities as well as outside city borders. Namely, (i) pre-industrial colonisers might struggle to persist in rapidly changing urban areas, limiting their foraging and breeding opportunities of the birds. (ii) Open habitats are under pressure of intensive agricultural exploitation in rural areas, which may negatively affect populations of less urbanized birds. In contrast, urban areas do not experience such pressure keeping the trends of urbanized open habitat species more positive. (iii) Differences in population trends between highly urbanized ground and above-ground breeders suggest that the latter may lose their breeding opportunities in modern buildings that do not provide suitable breeding sites. Our results indicate that even once successful, city dwellers may not keep pace with changes in urban areas, but these areas may also provide suitable habitats for biodiversity.

Abstract Empirical data are essential to assess the outcomes of management decisions in the context of adaptive management. We used flyway‐level population indices of a declining game bird to assess population changes after introducing hunting management measures as part of the European Union (EU)‐wide Adaptive Harvest Management mechanism (AHMM). In one flyway, a full hunting ban led to the start of population recovery; numbers increased by 25% in 2 years and the 10‐year population trend improved from “moderate decline” to “stable.” In the other flyway, harvest was only reduced (allegedly by 60% although statistics from key countries were incomplete), and numbers continued to fall (−15% decline). Our study shows positive results of the leading AHMM for a landbird in Europe and provides empirical evidence of the speed of population response and the timeframe needed for change to occur and to be detected. It showcases the successful application of policy mechanisms underpinned by science.

Detecting biodiversity change and identifying its causes is challenging because biodiversity is multifaceted and temporal data often contain bias. Here, we model temporal change in species' abundance and biomass by using extensive data describing the population sizes and trends of native breeding birds in the United Kingdom (UK) and the European Union (EU). In addition, we explore how species' population trends vary with species' traits. We demonstrate significant change in the bird assemblages of the UK and EU, with substantial reductions in overall bird abundance and losses concentrated in a relatively small number of abundant and smaller sized species. By contrast, rarer and larger birds had generally fared better. Simultaneously, overall avian biomass had increased very slightly in the UK and was stable in the EU, indicating a change in community structure. Abundance trends across species were positively correlated with species' body mass and with trends in climate suitability, and varied with species' abundance, migration strategy and niche associations linked to diet. Our work highlights how changes in biodiversity cannot be captured easily by a single number; care is required when measuring and interpreting biodiversity change given that different metrics can provide very different insights.This article is part of the theme issue 'Detecting and attributing the causes of biodiversity change: needs, gaps and solutions'.

This repository contains the input data, species level results and code associated with the paper: Drivers of the changing abundance of European birds at two spatial scales.

Abstract Although global assessments provide evidence of biodiversity decline, some have questioned the strength of the evidence, with local assemblage studies often showing a more balanced picture of biodiversity change. The multifaceted nature of biodiversity and imperfect monitoring datasets may partially explain these findings. Here, using an extensive dataset, we find significant biodiversity loss in the native avifauna of the European Union (EU). We estimate a decline of 17–19% in the overall breeding bird abundance since 1980: a loss of 560–620 million individual birds. Both total and proportional declines in bird numbers are high among species associated with agricultural land. The distribution of species’ population growth rates (ln) is centered close to zero, with numerical decline driven by substantial losses in abundant species. Our work supports previous assessments indicating substantial recent biodiversity loss and calls to reduce the threat of extinctions and restore species’ abundances, for the sake of nature and people.

This archive contain the two input datasets of bird population estimates and trend estimates underpinning the journal article: Abundance decline in the avifauna of the European Union reveals global similarities in biodiversity change. It also contains the species level results obtained from the Bayesian hierarchical model described in section 2.2.1 of the paper.

While global assessments provide evidence of biodiversity decline, some have questioned the strength of the evidence, with local assemblage studies often showing a more balanced picture of biodiversity change. The multifaceted nature of biodiversity and imperfect monitoring datasets may partially explain these findings. Here, using an extensive high-quality dataset, we find significant biodiversity loss in the native avifauna of the European Union (EU). We estimate a decline of 17-19% in overall breeding bird abundance since 1980: a loss of 560-620 million individual birds. Both total and proportional declines in bird numbers are high amongst species associated with agricultural land. The distribution of species’ population growth rates (ln) is centred close to zero with numerical decline driven by substantial losses in abundant species. Our work supports previous assessments indicating recent biodiversity loss and calls to reduce the threat of extinctions and restore species’ abundances, for the sake of nature and people.

In order to understand species' sensitivity to habitat change, we must correctly determine if a species is associated with a habitat or not, and if it is associated, its degree of specialization for that habitat. However, definitions of species' habitat association and specialization are often static, categorical classifications that coarsely define species as either habitat specialists or generalists and can fail to account for potential temporal or spatial differences in association or specialization. In contrast, quantitative metrics can provide a more nuanced assessment, defining species' habitat associations and specialization along a continuous scale and accommodate for temporal or spatial variation, but these approaches are less widely used. Here we explore relative habitat use (RHU) as a metric for quantifying species' association with and degree of specialization for different habitat types. RHU determines the extent of a species' association with a given habitat by comparing its abundance in that habitat relative to its mean abundance across all other habitats. Using monitoring data for breeding birds across Europe from 1998 to 2017; we calculate RHU scores for 246 species for five habitat types and compared them to the literature-based classifications of their association with and specialization for each of these habitats. We also explored the temporal variation in species' RHU scores for each habitat and assessed how this varied according to association and degree of specialization. In general, species' RHU and literature-derived classifications were well aligned, as RHU scores for a given habitat increased in line with reported association and specialization. In addition, temporal variation in RHU scores were influenced by association and degree of specialization, with lower scores for those associated with, and those more specialized to, a given habitat. As a continuous metric, RHU allows a detailed assessment of species' association with and degree of specialization for different habitats that can be tailored to specific temporal and/or spatial requirements. It has the potential to be a valuable tool for identifying indicator species and in supporting the design, implementation and monitoring of conservation management actions.

Around fifteen thousand fieldworkers annually count breeding birds using standardized protocols in 28 European countries. The observations are collected by using country-specific and standardized protocols, validated, summarized and finally used for the production of continent-wide annual and long-term indices of population size changes of 170 species. Here, we present the database and provide a detailed summary of the methodology used for fieldwork and calculation of the relative population size change estimates. We also provide a brief overview of how the data are used in research, conservation and policy. We believe this unique database, based on decades of bird monitoring alongside the comprehensive summary of its methodology, will facilitate and encourage further use of the Pan-European Common Bird Monitoring Scheme results.