Although horses evolved in North America, they went extinct 10 to 12 thousand years ago. Spanish conquistadors returned domestic horses to the continent in the mid-1500s, and since then, domestic horses have escaped captivity and also were purposefully released onto western rangelands where they thrive today. Most free-roaming horse populations are managed primarily by the Bureau of Land Management (BLM) of the U.S. Department of the Interior (1).

Non‐native species can have adverse impacts on native species. Predicting the potential extent of distributional expansion and abundance of an invading non‐native species can inform appropriate conservation and management actions. Non‐native mountain goats (Oreamnos americanus) in the greater Yellowstone area (GYA) have substantial potential to occupy similar habitats to native Rocky Mountain bighorn sheep (Ovis canadensis canadensis). To understand the potential for expansion of mountain goats in the GYA, this study evaluated detection‐nondetection data derived from ground‐based occupancy surveys of viewsheds partitioned into a grid of 100 × 100 m sampling units. Surveys were conducted over three summer seasons (2011–2013) in two study areas with well‐established mountain goat populations. Relationships between scale‐specific habitat covariates and mountain goat selection were evaluated to model occupancy and detection probabilities based on mountain goat detections in 505 of the 53,098 sampling units surveyed. Habitat selection was most strongly associated with terrain covariates, including mean slope and slope variance, at a spatial scale of 500 × 500 m, and canopy cover, heat load, and normalized difference vegetation index at a spatial scale of 100 × 100 m. These results provide new insight into multi‐scale patterns of mountain goat habitat selection, as well as evidence that mean slope and slope variance are more informative terrain covariates than distance to escape terrain, which has been commonly used in published mountain goat habitat models. The model predicted 9,035 km² of suitable habitat within the GYA, of which 57% is currently un‐colonized. Seventy‐five percent of all bighorn observations recorded in the GYA fall within predicted suitable mountain goat habitat. We also estimated that the GYA might have the potential to support 5,331–8,854 mountain goats when all predicted habitat is occupied, or approximately 2.5–4.2 times the most recent abundance estimate of 2,354.

We conducted experiments with captive female elk (Cervus elaphus) to explore the utility of allantoin:creatinine (A:C) ratios as a noninvasive index of nutrition in free-ranging ungulates. Pens of animals were assigned to one of four dietary treatments, each treatment being given to 6 animals. One treatment involved gradually increasing the daily metabolizable energy intake (MEI) from approximately 650 to 1200 kJ metabolizable energy (ME)/kg body mass (BM)^0.75in weekly increments over 8 weeks. In a second treatment, daily MEI was decreased in a similar manner from approximately 900 to 250 kJ ME/kg BM^0.75. Urine samples (96 in total) were collected from each animal in these treatments 5 days after each change in diet. Two additional treatments involved relatively large and abrupt changes in daily diet ranging from 120 to 500 kJ ME/kg BM^0.75, with successive diets being alternately increased and decreased at 2-week intervals for 10 weeks. Urine samples (179 in total) were collected from each animal 3, 5, and 13 days after a dietary change was initiated. The underlying relation between A:C ratio and MEI was consistent among the four treatments and indicated that the urinary A:C ratio is a reliable index of dietary intake in elk across a variety of dietary regimes. A:C ratios responded relatively quickly to changes in diet, indexing the dietary intake of the animals during a several-day period immediately prior to the time the urine was voided. The results of this and previous studies indicate that the urinary A:C ratio has significant potential as a nutritional index for wild ruminants; however, we recommend additional research before the use of A:C ratios is integrated into ecological or management applications.