Bird populations are declining globally with losses recorded in many European breeding birds. Habitat management measures have not resulted in a widespread reversal of these declines. We analysed national bird population trends from ten European countries (France, Hungary, Ireland, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland, and the UK) in relation to the species’ nesting strategy (‘ground-nesting' or ‘other’), Annex I designation (‘designated’ or ‘not designated’) and association with agricultural habitats for breeding (‘associated’ or ‘not associated’). For each country in our dataset, we also defined the following factors: farming intensity; predator community complexity; and predator control effort. Our results showed additive effects of nesting strategy, designation, and breeding habitats on the likelihood of population decline. Ground-nesting birds were 86% more likely to decline than birds with other nesting strategies. Annex I designated species of the Birds Directive were 50% less likely to decline than non-designated birds. Birds breeding primarily in agricultural habitats were more likely to decline than birds breeding in other habitats, interactively with farming intensity. Homogenous trends across Europe (i.e., trends in two or more countries that were either not declining in all countries or declining in all countries) indicate that the probability of population decline was related to nesting strategy and breeding habitat, with ground-nesting birds being 15.6 times more likely than other birds to have a declining trend across Europe, and birds nesting in agricultural habitat being 17.8 times more likely than birds nesting in other habitats to have a declining trend across Europe. Our results highlight a widespread challenge, therefore widespread instruments (e.g. legislation, economic policies, agri-environment schemes) will be required to reserve these declines. Ground-nesting species requirements can be complex and multiple strategies will be needed to restore populations including the development of predation management tools.

Many countries provide data to the Pan-European Common Bird Monitoring Scheme (PECBMS). We explored the PECBMS web page and the links included therein for each country, to identify if national data on population trends for each species could be obtained. Finally, we obtained national trends data for 10 countries, namely France (FR), Hungary (HU), Ireland (IE), the Netherlands (NL), Poland (PL), Portugal (PT), Spain (ES), Sweden (SE), Switzerland (CH) and the UK (UK). Specifically, common bird species trends in France were obtained from the monitoring programs coordinated by the Natural History Museum (http://www.vigienature.fr/fr/resultats-especes-3367). These data provided a 20-year trend (1998-2018) for each species. Hungary data from the Monitoring Centre of the Hungarian Ornithological and Nature Conservation Association were available at https://mmm.mme.hu/charts/trends and provided species trends for the period 1999-2021. Data from Ireland were available at https://www.npws.ie/sites/default/files/publications/pdf/IWM115.pdf and provided trends for 1998-2016 for each species. Netherlands data were obtained from the monitoring programs carried out by SOVON, the Dutch Centre for Field Ornithology (https://www.vogelwarte.ch/assets/files/publications/upload2019/Zustand%20der%20Vogelwelt%20in%20der%20Schweiz_Bericht%202019_E_low.pdf). These data provided species trends from 1990 to 2016.  Polish data were obtained from https://monitoringptakow.gios.gov.pl/database.html, and provided trends for each species for the period 2000-2019. Portuguese data (based on the program organised by the Sociedade Portuguesa para o Estudo das Aves, SPEA) were obtained from https://www.spea.pt/wp-content/uploads/2021/06/relatorio_cac_2021_vf3.pdf, as long-term (2004-2020) trends for each species. Data from Spain were obtained from the monitoring programs conducted by SEO/Birdlife (https://seo.org/boletin/seguimiento/boletin/2018/html5forpc.html?page=0), consisting of long-term trends (1998-2018) for each species. Data from Sweden, showing 1998-2022 trends for each species, were obtained from http://www.fageltaxering.lu.se/resultat/trender. Swiss data were obtained from the monitoring programs carried out by Vogelwarte, the Swiss Ornithological Institute (https://www.vogelwarte.ch/assets/files/projekte/entwicklung/zustandsbericht%202019/Zustandsbericht%202019_e_low.pdf) and consisted of 1990-2018 trends for each species. The UK data were obtained through monitoring programs at the British Trust of Ornithology (https://www.bto.org/our-science/publications/birdtrends/2020/species), providing long-term (1994-2020) trends for each species.

In all cases, trends for each species were categorised according to European Bird Census Council (EBCC) definitions (see https://pecbms.info/methods/pecbms-methods/1-national-species-indices-and-trends/1-2-production-of-national-indices-and-trends/trend-interpretation-and-classification) as ‘important decline’, ‘moderate decline’, ‘stable’, ‘moderate increase’, ‘marked increase’ or ‘uncertain. We regrouped the categories as ‘decline’ (either important or moderate) or ‘no decline’, (stability, moderate or important increase, or uncertain trends) to obtain a binomial variable describing the decline probability of a given species in each country.