Long-term reproductive data for forest and urban great tits – associated with Defrance et al article on selection

This dataset compiles long-term data on forest and urban great tit (Parus major) breeding phenology and reproductive performance. It includes standardized measures of first clutch laying date (FCLD) and reproductive output (clutch size and fledgling number), used to quantify differences in laying date between habitats and along the urbanization gradient, to estimate selection on this trait across habitats, and to characterize the probability of multiple brooding within a breeding season. The five data files contain complementary subsets: • FCLD_difference.csv: individual-level variation in laying date across years; • FCLD_difference_within_city.csv: spatial variation in laying date among urban study plots along an urbanization gradient; • selection_first_broods.csv: reproductive output of first broods only; • selection_all_broods.csv: annual reproductive output combining first and potential second broods; • multiple_brooding_proba.csv: occurrence of multiple brooding in relation to standardized laying date and habitat. Each dataset is accompanied by a `.txt` README file providing full details on variable definitions. This collection of datasets was used in analyses exploring the ecological and evolutionary drivers of reproductive timing and success in urban and forest great tits.