Urbanization is currently one of the most pervasive threats to biodiversity worldwide, yet traits permitting birds to exploit urban environments are not fully understood. I used bird traits related to diet (dietary item and foraging stratum), accounting for latitude, body size, development mode and phylogeny, to compare diet breadths of urban exploiters and urban avoiders, using a global dataset (463 bird species). Urban exploiters (urban species) were larger, consumed more vertebrates and carrion, and fed more frequently on the ground or aerially, and also had broader diets than urban avoiders (non‐urban species). In contrast, urban species had narrower foraging strata ranges than non‐urban species. These results not only support the hypothesis that urban species share dietary traits allowing them to cope with urban environments but also highlight the importance of considering multiple dietary traits to properly quantify species niches when assessing a species’ response to environmental change.

1. The widespread use of species traits to infer community assembly mechanisms or to link species to ecosystem functions has led to an exponential increase in functional diversity analyses, with >10,000 papers published in 2010-2019, and >1,500 papers only in 2020. This interest is reflected in the development of a multitude of theoretical and methodological frameworks for calculating functional diversity, making it challenging to navigate the myriads of options and to report details to reproduce a traitbased analysis. Therefore, the study of functional diversity would benefit from the existence of a general guideline for standard reporting and good practices in this discipline.2. We devise an eight-step protocol to guide ecologists in conducting and reporting functional diversity analyses. We do so by streamlining available terminology, concepts, and methods, with the overarching goal of increasing reproducibility, transparency and comparability across studies. The protocol is based on the following key elements: identification of a research question, a sampling scheme and a study design, assemblage of community and trait data matrices, data exploration and preprocessing, functional diversity computation, model fitting, evaluation and interpretation, and data, metadata and code provision.3. Throughout the protocol, we provide information on how to best select research questions and study designs, and discuss ways to ensure reproducibility in reporting results. To facilitate the implementation of this protocol, we further developed an interactive web-based application (stepFD) in the form of a checklist workflow, detailing all the steps of the protocol and providing tabular and graphical outputs that can be merged to produce a final report.

Species distribution models (SDMs) have become a workhorse to explain, understand and predict distributions of birds. However, SDMs at broad scales are typically built using climatic variables, while ignoring the effects of biotic interactions. Although its role still remains controversial, the inclusion of biotic interactions into SDMs could confirm and/or provide new ecological insights of poorly‐known species. We modeled the distribution of the rare South American straight‐billed reedhaunter Limnoctites rectirostris (Furnariidae), a specialist of marshy areas linked to the spiny herb eryngo (Eryngium spp., Apiaceae), which provides the main food and nest resources. To do this, we first modeled the distribution of three eryngo species considered as the main biotic interactors (E. eburneum, E. horridum and E. pandanifolium) and included them into the straight‐billed reedhaunter SDM. Second, we analyzed niche overlap between the straight‐billed reedhaunter and eryngos in terms of environmental variables using dynamic range boxes, a novel approach to quantify size of n‐dimensional hypervolumes. The inclusion of biotic interactions improved model performance relative to a model with climatic variables only. Climatic suitability of E. eburneum and mean temperature of wettest quarter were the most important predictors. By contrast, E horridum and E. pandanifolium resulted in poor predictors, suggesting that the straight‐billed reedhaunter's relative dependence on each eryngo species is different. The three eryngo environmental spaces largely covered the environmental space of the straight‐billed reedhaunter, but the opposite was not true. Our findings suggest that biotic interactions play an important role in explaining and predicting the distribution of a rare bird at macro‐scales, and that the assessment of niche overlap between interactors may confirm or improve the autoecological understanding of rare and cryptic birds. We advocate the use of an integrative modeling approach including climate and biotic interactions into SDMs to enhance ecological knowledge on poorly‐known bird species.