Recruiting age influences male and female survival and population persistence in a long-lived tropical seabird

Abstract

Variation in the age at first reproduction may have important implications for growth and dynamics of populations, but these potential impacts remain virtually unexplored. By using 26 years of data from a marked colony of blue-footed boobies Sula nebouxii (Milne-Edwards), we tested whether survival of early recruits is lower in comparison to late recruits, and investigate how different recruiting ages contribute to the persistence of the population. In addition, we simulated changes in the age at recruitment and estimated their impact on population fitness. Our analyses of 1310 capture–recapture histories revealed that the younger males and females initiated reproduction within the first 6 years of life, the lower were their mean annual survival probabilities. Survival did not differ between the sexes and the impact of recruiting age on survival was similar for males and females. Each additional year that male and female boobies delayed the start of reproduction meant an increase of roughly 2 % in their annual survival rates. Male and female recruits 2–5 years old contributed the same to the rate of population growth (λ) regardless of their particular age, but the contribution to population growth started to decline from age 6 years. According to our simulations, delaying reproduction beyond 5 years in the case of females, and beyond 6 years in the case of males, would negatively affect this booby population. Therefore, we suggest that there is selection against recruiting beyond 5–6 years old. This study adds to the nascent empirical literature on long-term fitness consequences of variation in the age at first reproduction in long-lived species, and provides insights into evolution of early and late reproduction and trade-offs from a demographic perspective.