Assessment of ecological factors influencing the winter habitat suitability of Erithacus Rubecula across Europe through ecological niche modeling

Abstract

Erithacus rubecula (European robin) is a common songbird from Europe and found in North Africa and Western Asia. Easily recognizable with its typical orange throat and melodious song, its winter ecological niche is not fully understood yet. Moreover, the European robin is what we call a "facultative non-breeding partial migrant", meaning that in one population, some individuals will show a migratory behavior whereas others will not. In addition, that status can vary from one year to another for a certain proportion of the population. Across this master thesis, the goal was to determine which abiotic and, less importantly, biotic factors are driving the winter habitat suitability of the European robin and what impact those factors could potentially have on its migratory behavior. I worked with the ecological niche modeling tool in R studio and Maxent/ GLM as algorithms to achieve this goal. The occurrences data were downloaded from the eBird Observation Dataset loaded on GBIF; the abiotic variables were downloaded from the WorldClim website and the biotic variables from the land-cover MOD44B. Once the variables and the algorithm settings were selected, models were fitted, assessed, statistically evaluated, and the habitat suitability maps were plotted. The results showed that even though the abiotic factors were the primary concern of this study, they explain 57% of the winter habitat suitability of the robin, which is less than was expected. Land-cover was thus also greatly contributing to characterize the ecological niche of the robin. Moreover, the temperature seasonality, the mean temperature of the coldest quarter, and the absence of land-cover had the most significant impact on the habitat suitability. Studies led in Belgium, Spain, and Portugal found that females and juveniles had greater chances to express a migratory behavior. Nevertheless, we can suggest that a high seasonality over the year, temperatures below 0.5°C and above 16.53°C, and a lack of vegetation superior to 40% could highly contribute to greater chances of witnessing migratory behavior of an individual. However, whether those variables im- pact the robin directly or indirectly requires further investigations which were not realized in the context of this master thesis.