The population genetics and breeding biology of the European nightjar

Ecological and life history traits influence a species’ vulnerability to population decline, with long-distance migratory birds and resource specialists at particular risk. Population genetic variation is imperative for population persistence and is ultimately maintained and regulated through population size, connectivity, and breeding behaviour. In this thesis I investigate the demographic history, spatio-temporal population genomics, genetic mating system and mate choice in a resource specialist, long-distance migratory bird, the European nightjar (Caprimulgus europaeus). Using Pairwise Sequentially Markovian Coalescence analysis applied to two nightjar genomes, I show that C. europaeus has been subject to significant climate driven changes in population size over the last 5 million years. Genomic analysis of museum and modern samples showed a significant 34.8% decline in genome-wide heterozygosity and shift from panmixia to weak spatial structuring in the British population over the last two centuries, likely owing to habitat loss and fragmentation. Nightjar were found to exhibit social monogamy and moderate extra-pair paternity rates (EPP; 23% of offspring were extra-pair) at two breeding populations in Britain, with EPP significantly higher where male density was elevated. As in most Caprimulgids, male nightjars display prominent white spots on the outer primary and rectrices. White spot size was found to correlate with age in male nightjars. Sires of extra-pair offspring possessed significantly smaller (16%) spots than birds who secured paternity with their social partners. My results suggest that EPP in nightjars is likely secured by lower-quality floater males, which is in alignment with my finding that male but not nest density correlated with EPP rate. My work reveals the genomic signature of population decline likely shared among long-distance migrants and resource specialists, highlighting the need for a wider application of genomic analysis across other species with similar life histories, particularly at range extremes. My results suggest that increasing connectivity between breeding grounds could reduce the genetic structuring and reverse the decrease in genetic diversity that has arisen in the last 200 years. With appropriate management, conserving range extreme populations may be valuable in preserving adaptive variation imperative for range expansion under future climate change scenarios.