Mammals and Birds : Lifespans of Wild Populations 93 



When we compare these survival curves, we can quite 

 clearly distinguish some interesting similarities and differences. 



(1) A very steep initial slope, indicating a very high mortal- 

 ity during the first year of hfe, is found in both sexes of all the 

 species. The actual mortality rate for calves is probably even 

 greater, since their skulls ar^ more easily overlooked and more 



Fig. 3. Survival curve graduated on a logarithmic scale, 

 for a series of 292 barren-ground caribou. 



quickly destroyed than those of the adults. This age class is 

 therefore quite probably under-represented in most samples. 



(2) During the second year of life there is a small loss in both 

 sexes of all species, with but two exceptions, that of the male 

 roe deer where there is emigration and that of the male black- 

 tailed deer of the Californian chaparral where some yearlings 

 are killed. 



(3) During the third year of life there is a heavy loss among 

 male and female roe deer and male black-tailed deer from both 



