The Biology of Senescence 



in the first year. This compares with a maximum recorded age 

 of 11 years, which is occasionally reached in the wild state. 

 The succeeding annual mortality was at a steady rate approach- 

 ing 50 per cent. A survivorship curve for lapwings (Vanellus 

 vanellus) calculated from 1333 birds is closely fitted by a line 

 corresponding to a constant mortality of 40 per cent per annum 

 (Kraak, Rinkel and Hoogerheide, 1940; Lack, 1950). The rates 

 of mortality for most birds which have been studied appear to 

 fall between 30 and 60 per cent per annum. Very much lower 

 figures have been recorded for large sea birds such as cormorants 

 (Kortlandt, 1942) in which the mortality was found to decline 

 from 17 per cent before fledging to an annual rate of 4 per cent 

 between the third and twelfth years. The annual mortality in 

 one species of albatross (Diomedea epomophora) is only 3 per cent. 

 Such birds may well live to reach senescence, if their life-span 

 is 50 years. But considerable evidence has accumulated, chiefly 

 from ringing studies, to show that the expectation of life of 

 some wild birds actually increases with age. Although the total 

 of ringed birds recovered in Europe does not exceed 10,000 per 

 year, a few individuals are known to have survived for longer 

 than could be expected if the early mortality were maintained. 

 R. Perry (1953) gives records of this kind (Redwing — Turdus 

 musicus, 17+ years; goldfinch — Carduelis carduelis, 16+ years; 

 meadow pipit — Anthus pratensis, 13 years) all of them in species 

 which have mean annual survivals of the order of 50 per cent 

 (Lack, 1950). A ringed starling [Sturnus vulgaris) has been re- 

 taken after 18 years. The probability of such records being 

 obtained as a result of chance, bearing in mind how few birds 

 are ringed, is very low indeed. An almost exactly similar situa- 

 tion has been observed in the human population of the Punjab, 

 where, in spite of a very heavy early and adult mortality, very 

 old individuals are not uncommon, and those who survive 

 beyond middle life have an expectation of life comparable to 

 that in Western Europe (Yacob and Swaroop, 1945). 



In lizards, the wild mortality rate declines with increasing 

 age (Sergeev, 1939): this result agrees with the ecological 

 studies of Stebbings (Stebbings and Robinson, 1946; Stebbings, 

 1948) on Sceleporus graciosus in the wild. A very high proportion 

 of the population was found to consist of lizards 6 to 9 years 



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