A global analysis reveals the dynamic relationship between sexual selection and population abundance in space and time

Sexual selection leads to the evolution of extravagant weaponry or ornamental displays, with the bearer of these traits gaining a reproductive advantage, potentially at a cost to the individual’s survival. The consequences of sexual selection can therefore impact species demographic processes and overall abundance. Currently, evidence connecting the effects of sexual selection to demography and abundance is conflicting. This study aims to rectify this issue by assessing the relationship between sexual selection and abundance in Passerines across the globe, importantly, accounting for migration and seasonality. We integrate a global citizen science dataset of bird observations with Passerine trait data to show that migration and seasonality are key moderators in the relationship between sexual selection and abundance. For resident Passerines, the relationship is consistently positive across the year, whereas for migrant Passerines, the relationship is overall neutral, with a significant negative dip during pre-breeding migration (for Northern Hemisphere Passerines). Our results suggest that sexual selection bolsters populations that experience less intense natural selection.