Annual apparent survival across species is lower in juvenile than adult birds but has similar ecological correlates

Abstract

Annual survival is a key demographic trait influencing population growth and viability. Variability among species in annual survival tends to reflect different life history trajectories. In adult birds, greater annual survival has been shown to be associated with larger body mass, smaller clutch size, lower latitude, island living, flocking and cooperative breeding. Less attention has focused on the ecological correlates of survival in birds during the first year of life. Using a phylogenetic framework, I explored the correlates of annual juvenile survival across species worldwide. When measured concurrently at the same study sites, annual apparent survival in a sample of 338 species was strongly and positively associated with body mass and was typically at least half of adult survival. Lower annual survival in juveniles probably arises through inexperience, but mortality might be overestimated as juveniles tend to disperse more extensively than adults. In a separate analysis involving 610 survival estimates from 342 species, I examined the ecological correlates of annual apparent survival in juveniles. With the exception of migration, most ecological correlates of annual apparent survival in adults, such as body mass, latitude and island living also prevailed in juveniles. The findings support the idea that the ecological factors associated with greater survival in adults are similar in juveniles.