Body mass dynamics of migratory nightjars are explained by individual turnover and fueling

''Body mass Red-necked Nightjars'' dataset includes measurements from a long term study (2011-2019, N = 882 measurements) taken in a population of Red-necked nightjars (<i>Caprimulgus ruficollis</i>) in Doñana National Park, located in the southwest of the Iberian Peninsula. The weight and the stomach (gizzard) volume were measured from the captured individuals. ''Capture-recapture data for calculation of FDR'' datased includes measurements from this same long term study (2011-2019, N=166 measurements) of Red-necked Nightjars. In this dataset, only individuals recaptured after 24.00 pm were included and body mass were corrected for stomach (gizzard) size. Further details on the field procedures are provided in the article.<br>