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DISCUSSION 



Rotblat : Is anything known about the lifespans of the same species 

 in captivity ? 



Bourliere: Not for the swift, because it is at present impossible to 

 keep them caged. What we have are good figures on the maximum 

 lifespan of some individuals. We also know that in both large and 

 small mammals and birds the maximum lifespan in captivity is 

 always far greater than in the wild. Nevertheless, in wild popula- 

 tions, at least in those species for which we have data, a very small 

 percentage of very old individuals is found ; but in order to find these 

 very scarce old animals, you need to study a very large population 

 for a very long time. 



Rotblat: I understand that bats kept in zoos live much longer than 

 the 20 years which you mentioned for the albatrosses. 



Bourliere: Twenty-five years is the longest recorded lifespan for 

 the royal albatross in the wild in New Zealand, but as far as I know, 

 nobody has ever kept an albatross in captivity for more than a few 

 years because it is very difficult to feed them. 



Comfort: A chaffinch has been kept for 29 years (Moltoni, E. 

 (1947). Riv. ital. Orn., 17, 139), and even an inbred budgerigar is 

 reported to have reached nearly 20. 



Scheidegger: One swift in a big colony near Basle lived for 18 years, 

 but the rest had an average age of about 5 to 6 years. 



Danielli: Your remarks about birds which survive longest being 

 large does not fit in with data for the swift, as you pointed out. Prof. 

 Bourliere. Do you attribute the advantage the swift seems to possess 

 to the fact that it more or less hibernates ? 



Bourliere: That explanation was advanced by Farner (1955) and 

 it may be true because we have the very same phenomenon in 

 mammals. We may compare rodents and bats of similar size and 

 weight. Small mice, for instance, never live in captivity or in the 

 wild for more than four years, whereas bats of the same weight will 

 live for 20 years ; so there is certainly some correlation between a long 



