THIS CHAPTER DISCUSSES THE REPRODUCTION and population structure
and dynamics of Yellowstone bison during the period 1964-68. A
series of bison reductions from 1961 through 1965 consistently
removed a large number of breeding-age females. Records indicate
that the reductions by field shooting of the mid-1950s also did
this, as did some of the earlier removals at the Buffalo Ranch
in Lamar (Table 9). Some population characteristics may change
after a period without reductions. Data for all categories were
not obtainable each year; hence, selected figures are used in
some instances to suggest population conditions. TABLE 9. Number
of cows and calves removed during reductions. bTotal classified
(bulls, steers, calves) not necessarily total reduction number.
Incidence of pregnancy by age class for two Yellowstone studies
25 years apart are compared in Table 10 as an indication of
sexual maturity in the female population. The 1940-41 study
sampled the semiranched population of Lamar; the 1964-66 study
sampled the