Senescence and Reproductive Value in Sparrowhawks

A long-term study of marked individuals in a numerically stable Sparrowhawk breeding population enabled the reproductive and survival rates of females of different ages to be calculated. These estimates were then used to calculate reproductive value, the mean number of young produced by females of different ages during the rest of their lives. The data provided evidence, not only for improvement in survival and breeding success in the early years of life, but also for senescence, i.e., a deterioration in survival and breeding success later in life. Average annual survival increased from 0.49 in 1st-yr females to 0.66 in 4 yr olds, and declined to 0.28 in 9 yr olds (maximum life-span 10 yr). Average annual production of young increased from 0.3 in 1st-yr females (including nonbreeders) to 3.3 in 5 yr olds, and declined to 1.8 in 9 yr olds. Mean reproductive value increased from 3.1 in 1st-yr females (including nonbreeders) to 8.1 in 4 yr olds, and declined to 2.1 in 9 yr olds.