SENESCENCE AND REPRODUCTIVE VALUE IN SPARROWHAWKS

A long-term study of marked individuals in a numerically stable Sparro whawk breeding population enabled the reproductive and survival rates of females of different ages to be calculated. These estimates were th en used to calculate reproductive value, the mean number of young prod uced by females of different ages during the rest of their lives. The data provided evidence, not only for improvement in survival and breed ing success in the early years of life, but also for senescence, i.e., a deterioration in survival and breeding success later in life. Avera ge annual survival increased from 0.49 in Ist-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 Ist-yr female s (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 Ist-yr female s (including nonbreeders) to 8.1 in 4 yr olds, and declined to 2.1 in 9 yr olds.