Horn Growth and Population Quality in Dall Sheep

Abstract

Measures of horn growth of Dall sheep (Ovis dalli dalli) are compared with physical, demographic and meteorological measurements. Horn growth is not correlated with body size in either ewes or rams. Rams showing rapid early growth of horn show slower subsequent growth. Gradual wear influences the measured length of the lamb annulus in both ewes and rams. Horn growth is a function of precipitation, implicating primary production and shows marked differences between years. Differences are correlated with recruitment. Horn growth of rams is strongly affected by differences in environmental conditions between years than is horn growth of ewes. In good years, growth is enhanced uniformly over all ram age-classes; in poor years growth in younger age-classes is depressed more severely than is growth in older age-classes. Condition of the dam can affect horn growth of rams for a period of at least 5 yr following birth. Useful indices of quality can be constructed from measurements such as length of annuli provided the lamb annulus is ignored and affects of calendar year are acknowledged. Measures presented argue for the importance of range quality in the production of trophy animals.