Ageing in house sparrows is insensitive to environmental effects

Variation in individual life histories, and physiology, determines the rates at which new life is generated (reproduction) and lost (death) in a population. Studying the demography of deaths thus reveals fundamental aspects of the biology of individuals within a population. We studied mortality senescence, the increase in mortality rate with age, in wild and captive house sparrows (Passer domesticus), and demonstrate highly similar mortality senescence in both, but markedly lower vulnerability to death (frailty) in captivity. This suggests that house sparrows have a species-specific rate of ageing that is insensitive to environmental effects. Unexpectedly, juvenile and adult mortality co-varied positively across years in the wild, indicating that mortality is not strongly density-dependent. Mortality also varied widely among years, suggesting a strong environmental effect, and we explain the observed patterns using temperature data and predation by birds of prey. We discuss how stochastic environmental effects can affect the evolution of ageing.