Mountain Sheep Survey Methods

North American mountain sheep (bighorn [ Ovis canadensis ], thinhorn [ Ovis dalli ]) have played prominent roles in the ecology and culture of human beings for millennia. Dating to the Holocene, we suggest hunters and gatherers likely were among the first to develop index-level approaches to the abundance of mountain sheep and other ungulates, an apparently novel concept. As the exploration of North America progressed, the presence of wild sheep became of increasing interest, leading to descriptions of multiple species, estimates of numbers, and the evolution of methods of conducting surveys to better determine their abundance. From the rock art of the earliest North Americans to the advent of aerial surveys, and the later technological achievements such as thermal imaging, progress in survey methods has been constant, while the objective of understanding how many sheep there are continues. In this chapter we emphasize the methods used to obtain the raw numbers that statisticians and modelers employ to derive population estimates. In doing so, we explore the history of the application of those methods, provide insight into the advantages and disadvantages of the various methods that have been used, or currently are in use, to obtain information on the numbers of mountain sheep, and in the end raise questions about the level of precision necessary to conserve and properly ensure the persistence of mountain sheep in a constantly changing world.