Long-term reproductive data for forest and urban great tits – associated with Defrance et al 2026 Journal of Animal Ecology article

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.