Range dynamics of the European Bee-eater (Merops apiaster)
When environmental conditions change, species usually face three options: adaptation, range shifts, or extinction. In the wake of climate change, it is generally believed that range shifts are the norm in mobile species such as birds, resulting in poleward range shifts. The European Bee-eater is a predominantly Mediterranean species which has expanded its range to higher latitudes over the last decades. Germany in particular has seen a surge in breeding pairs and foundation of new colonies. However, while many experts suggest climate warming as the main driver behind this range expansion, an explicit quantification remains open. Here, we use an ensemble modelling approach to study the recent climatic niche suitability of the European Bee-eater across Europe with a special focus on Germany and project its predicted Palaearctic breeding distribution onto the year 2050 using two global circulation models and two representative concentration pathways. Models were able to predict the current European range of the species with some underestimated areas in Central and Eastern Europe, depending on the selected model. We found a strong relationship between climatic suitable areas and estimated population sizes across European countries that is reflected in most algorithms. In particular, the German population size is in line with climate suitability in the country suggesting a strong climate–population relationship and a high degree of niche filling. Most future predictions point to an ongoing northward expansion of the species while areas in Southern Europe and the Maghreb area remain largely suitable. The strong climate–population relationship makes the European Bee-eater an appropriate indicator species for climate change. Yet the high variability of modelling algorithms also call for caution of using these techniques without careful inspection.