Predicting the breeding distribution of wader species across climatic and environmental gradients

Developing and applying species distribution models is particularly urgent for species currently facing high levels of environmental change. Waders (Charadrii) are among the most species‐rich groups of birds breeding at higher latitudes and the one where species are declining fastest. Iceland holds a large part of the global population of several wader species breeding sympatrically across unique climate and environmental gradients. This provides a rare opportunity to assess synergy (i.e. commonality) in habitat selection and occurrence of species usually occupying wide latitudinal ranges from temperate to Arctic. In addition, Icelandic wader habitats are facing significant and increasing pressures from anthropogenic sources putting in risk these populations. In this study, we used occurrence data for several waders and a set of bioclimatic and biophysical covariates to generate species distribution models (SDM) using Bayesian additive regression trees. We found that most species were more likely to occur in the lowlands on flatter areas, with some vegetation cover and near water, and that species with a more northerly global distribution were more common in the colder and barren highlands, whereas the temperate species were almost solely restricted to the warmer lowlands. The distribution models presented here show that there is considerable overlap in the occurrence of species which generally occupy different regions globally. All are more likely to occur on flat, wet areas with some short vegetation. The results also highlight the international importance of the Icelandic lowlands for breeding waders, areas where most anthropogenic pressures are also concentrated.