Code and data for: No evidence of reproductive senescence within the natural lifespan in resident mountain chickadees (Poecile gambeli)

Reproductive aging in vertebrates is commonly characterized by an increase in reproductive performance early in life and a decline in reproductive performance late in life (i.e. senescence). However, some species do not seem to exhibit reproductive senescence, and others even exhibit increased reproductive performance throughout their lifetimes. Our understanding of the mechanisms that underly this variation in different species remains limited, in particular whether these patterns are driven by female or male contributions to reproduction in sexually-reproducing taxa. Here we report results from a longitudinal study on the relationship between age and reproductive performance in a wild, resident songbird. Our dataset included 698 breeding attempts from 551 unique mountain chickadee (Poecile gambeli) pairs composed of individuals aged 1 through 9 years old. First egg dates, clutch sizes, and brood sizes varied most with female age, whereas mean fledgling mass was best predicted by male age. Both female and male reproductive performance were positively associated with age, but the processes underlying these patterns differed between the sexes. Long-lived individuals of both sexes exhibited higher reproductive performance than short-lived individuals, but females also showed within-individual improvements in reproductive performance with age. In contrast, individual male reproductive performance remained stable with age, suggesting the observed population-level positive association in males was a result of lower survival of low-quality breeders. Our results reveal a lack of reproductive senescence in mountain chickadees within their naturally-observed lifespans and show that age-related reproductive patterns of both sexes can contribute to the reproductive performance of breeding pairs.