From 1923 to the present, bison in excess of the carrying capacity of the Park have been removed from the herd. Initially, in the 1930's and 1940's, the old, sickly and deformed bison were culled from the herd. In the 1950's through the 1980's, an attempt was made to reduce the herd proportionately in all age groups. The Park now seeks to maintain a 50/50 sex ration and tries to annually cull yearlings, leaving 8-10 males and females in the Park. Click here to view a video clip of the bison capture operation.