Alarming conservation status of Western European steppe birds and their habitats: An expert-based review of current threats, traits and knowledge gaps.

Abstract

European steppe birds are facing unprecedented declines, positioning among the most threatened bird groups. We provide a comprehensive review and synthesis of the available knowledge on Western European (WE) steppe birds, focusing on their ecology, functional traits, population range trends and major threats. Using an expert-based participatory approach, we first created a consensual list of 37 WE species and reviewed the current knowledge on these key topics. Although 67.6 % of species show declining population ranges, only 18.9 % are classified as Endangered or Vulnerable according to the European IUCN Red List. Notably, several species exhibit range contractions over 5 % yet remain listed as Least Concern, indicating a need for re-evaluation based on the most up-to-date data. Threatened species have distinct functional traits compared to non-threatened species, typically being sedentary, large-bodied, long-lived, and exhibiting ground-foraging and ground-nesting behaviours. This highlights the potential for functional diversity loss if threatened species become extinct. Species experiencing the greatest range contractions share many of these traits or exhibit arboreal or aerial lifestyles, carnivorous diets and partial to fully migratory behaviours. Experts identified land use change and human- caused mortality as the main threats, followed by pollution and climate change, although the effects of the latter remain poorly understood for most species. Because significant knowledge gaps on climate and pollution effects remain for most species, these two threats should be the focus of future investigations. This synthesis enhances our understanding of the threats faced by WE steppe birds and provides guidance for prioritizing future research and conservation efforts.