Joshua Whitaker and Dr. Todd F. Robinson, Plant and Wildlife Sciences
Introduction
Over the course of the last few months the final foraging samples have been collected on five populations of bighorn sheep (Ovis canadensis) in the Great Basin and along the Wasatch Front. These locations include the Newfoundland Mountains, Antelope Island, American Fork Canyon, Rock Canyon, and Mt. Nebo. The purpose of this project was to develop an idea of the foraging habits of these different herds, and within the Antelope Island herd, determine the differences in foraging habits between age and sex classes. By no means is this intended as a complete final report, but rather as preparations for a Master’s Thesis potentially involving the use of stable isotopes from the forage samples and hairs collected from ewes in each of the ranges. Hair samples from rams, ewes and yearlings were collected on Antelope Island and will be used to compare differences in use by the respective groups.
Methods
Forage samples were taken according to Flinders and Hansen (1972). Namely, bighorn sheep were observed while foraging and a map of the location was drawn. After the animals had moved from the site researchers centered a circular 1 m2 quadrat over the actual forage site and clipped all forage within the quadrat to ground level, bagged and weighed each plant species independently. Before clipping, estimates were made of percent use of biomass and percent cover by species. For each site sampled a random site (a random direction and distance) was obtained using a random digits table and was sampled in the same manner to provide information as to what the actual makeup of each forage area was. Once collected, all samples were dried at 60°C for 24 hours to obtain dry weight.
All samples will be ground to obtain a 100 microgram subsample which will subsequently be run through a mass spectrometer to determine the stable isotopes present within each plant species. Hair samples already collected from each population will be cut into 1mm pieces and also run through a mass spectrometer. The corresponding spikes in different stable isotopes will provide information as to what plant species were consumed. The relative time of consumption of each species can be known by comparing the growth rates of the hairs and the location along the hair where the spike occurs (Robinson, 2007). The exact details of this part are not yet known in detail, as a lab assistant will be instructing in correct procedure.
Comparing stable isotopes will help create a key to identify the plant components of an animal’s diet. This key removes the need for direct observation and forage sampling.
Results
340 forage sites were sampled, as were 340 random sites from August of 2005 to December of 2006. All the forage collected has been dried and is awaiting reweighing to obtain dry weights and then will be ready to be ground and encapsulated for the mass spectrometer.
Conclusion
As this study is continued as a Master’s project it will help streamline the study of forage use by bighorn sheep. It will no longer require the time, manpower, and money to determine forage use. Instead, a hair sample will tell us what an animal ate and when.