50 



100 



150 



200 



Fig. 9.- 



Night 



-African Ibis ( Threskiornis aethiopicus) . Survival of 2 1 individuals — 



sexes combined (London Zoo) • — • 

 Heron {Nycticorax nycticorax). Survival of 17 individuals — sexes 

 combined (London Zoo) — 0. 



24 



18 



16 



12 



8 



DAYS 

 Fig. 10, 



100 



200 



300 



400 



500 



600 



700 



800 



-Orkney Vole (Microtus orcadensis) . Survival of 24 individuals- 

 sexes combined (London Zoo). 



