DOI: 10.5061/dryad.xpnvx0kkp
title: Wader breeding densities across European habitats

description: Wading birds can be found breeding in a myriad of habitats and ecosystems
 across Europe that vary widely in their land-use intensity. Over the past
 few decades, wader breeding populations have declined steeply in habitats
 ranging from natural undisturbed ecosystems to intensively managed
 farmland. Most conservation science has focused on factors determining
 local population size and trends which leave cross-continental patterns
 and the associated consequences for large-scale conservation strategies
 unexplored. Here, we review the key factors underlying population decline.
 We find land-use intensification in western Europe and mostly agricultural
 extensification and abandonment in northern, central and eastern Europe to
 be important drivers. Additionally, predation seems to have increased
 throughout the breeding range and across all habitats. Using collected
 breeding density data from published and grey literature, we explore
 habitat specificity of wader species and, of the most widely distributed
 species, how breeding densities change across a land-use intensity
 gradient. We found that two-thirds of all examined wader species have
 relatively narrow breeding habitat preferences, mostly in natural and
 undisturbed ecosystems, while the remaining species occurred in most or
 all habitats. The most widespread generalist species (black-tailed godwit,
 northern lapwing, common redshank, Eurasian oystercatcher, common snipe
 and ruff) demonstrated peak breeding densities at different positions
 along the land-use intensity gradient. To conserve both diverse wader
 communities and viable meta-populations of species, a diversity of
 habitats should be targeted ranging in land-use intensity from natural
 ecosystems to medium-intensity farmland. Alongside, strategies should be
 designed to moderate predation of wader clutches and chicks.
description: To examine which habitats waders use for breeding in their main
 distributional range in Europe, how this differs between species and
 whether different habitats support different population densities, we
 searched published papers for quantitative data that could be used to
 calculate breeding densities. Initially, we performed searches of
 peer-reviewed scientific articles reporting densities of breeding waders
 published between 1945 and 2018 using ISI Web of Science Core Collection
 (WoS) and Elsevier Scopus databases by using a specific combination of
 related keywords (see Appendix
 1 for more detailed information). We only used studies that
 met the following requirements: (1) the study reported breeding pair
 density data or gave a number of breeding pairs for a certain specified
 area from which a breeding density estimation could be calculated; (2) the
 study described which methodology was used for surveying breeding birds;
 (3) the study specified the habitat type or vegetation composition of the
 surveyed area; (4) the study mentioned the year(s) of survey. We focused
 on continental Europe, including the United Kingdom and Ireland but
 excluding Iceland. Although southern Europe has some locations supporting
 breeding waders (e.g. Tinarelli and Bacetti, 1989; Valle and Scarton, 1996), we were not able to find breeding density information in any country located in the Mediterranean area. In total, we found 32 scientific articles containing 984 breeding densities that included 26 wader species and 5 countries in the period 1967–2015. In line with previous observations (Tryjanowski et al., 2011), we found most studies originated from the United Kingdom (65% of all data). The other represented countries were Poland (10%), Finland (11%), Sweden (10%), European Russia (3%) and France (1%). Surprisingly, hardly any studies were found from countries such as the Netherlands, a renowned stronghold of wader species such as black-tailed godwit, northern lapwing and Eurasian oystercatcher (Roodbergen and Teunissen, 2019), with various scientific groups working on meadow bird ecology. In most countries, it is common practice to report results of breeding wader surveys in local reports or journals in the national language. We therefore decided to include grey literature in our review, acknowledging that this biases our findings somewhat to languages that are accessible to the authors (Dutch), mostly from northwestern Europe. Data from non-peer reviewed conference papers and government reports were searched on common search engines such as google scholar database using the same combination of keywords as was used for peer-reviewed papers. Our final dataset contained 87 studies, 29 species and 8 countries with a total of 2,744 breeding density observations