Metabarcoding reveals selective dietary responses to environmental availability in the diet of a nocturnal, aerial insectivore, the European Nightjar. Faecal metabarcoding data for diet exploration of the European nightjar

Many avian species are vulnerable to environmental change. Knowledge of vulnerable species’ diet, and variation therein, can provide an understanding of population status and flexibility to respond to change. Insectivorous species are predicted to have a flexible diet within and between individuals, which can respond to naturally fluctuating prey abundance, thus allowing opportunistic exploitation of available resources. We analysed the diet of a nocturnal, aerial insectivore, the European Nightjar (Caprimulgus europaeus), using high-throughput metabarcoding. We quantified dietary diversity and composition of 130 faecal samples from nests and roosts, on a northern breeding site in the UK from 2015 – 2018, and compared differences among individuals and years. Although dominated by moths, Nightjar diet varied significantly between individual faecal samples and between years and months. Prey species composition varied between years, and was more variable between samples in 2017, compared to other years. Faecal samples were significantly more likely to contain moth species with a wingspan of >60mm and significantly fewer moth species of <25mm wingspan. This indicated size selective foraging by Nightjars, which also varied between months and years. Nightjar diet was driven by inter-individual variation, indicating population flexibility in prey choice. Metabarcoding provided a valuable tool in the exploration of insectivorous diets, but efforts are needed to build comprehensive reference libraries, in order to compile full prey species lists.