Any opinions expressed in this memoir are those of the author(s) and do not necessarily reflect the views of the National Academy of Sciences. r o B e r t h o f s t a d t e r Biographical Memoir Copyright 1994 national aCademy of sCienCes washington d.C.

Repeated censuses of a population of yellow baboons (Pupio ~ynocephalri~s) in Amboseli National Park, Kenya, revealed a decrease from over 2,500 animals in 1963-1964 to 123 individuals in 1979, or from a density of about 73 to 1.8 baboons per kmz over a 15-year period. Median group size decreased from 43 in 1964 to 27 in 1979. The largest and smallest goups declined the most; groups near the me...