Theses and Dissertations at Montana State University (MSU)
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Item Development of occupancy surveys for mountain ungulates(Montana State University - Bozeman, College of Letters & Science, 2013) O'Reilly, Megan; Chairperson, Graduate Committee: Robert A. GarrottBighorn sheep (Ovis canadensis canadensis) and mountain goats (Oreamnos americanus) overlap in broad food and habitat requirements. In places where mountain goats are non-native there are concerns over potential competition between the two species. The southern Gallatin Mountain range, within and adjacent to the northwest boundary of Yellowstone National Park has both native bighorn sheep and non-native mountain goats. Existing observations of both species for this area vary in spatial precision and there are no records of where observers looked for animals but did not detect them. To gain a better understanding of the relationship between bighorn sheep and mountain goats and their habitat, it is necessary to understand resource selection and the extent of overlap in resource use at fine spatial and temporal scales. I used logistic regression to relate existing presence-only bighorn sheep and mountain goat data for this area to landscape features I expected would be important to both species. Using resulting coefficient estimates, I constructed a relative habitat suitability map and used it to define four survey regions within the study area. The crew of four spent 113 observer days afield and hiked 210 miles recording occupancy data for both mountain ungulates within these four survey regions. Observers surveyed 6,603 100 x 100 meter grid cells, with 15 groups of bighorn sheep and 34 groups of mountain goats observed during surveys. Because there were more mountain goat observations available, I used only mountain goat data to conduct formal occupancy analyses. Mountain goat occupancy was positively associated with ruggedness at the 100 meter scale and there was an important interaction between distance to escape terrain and tree cover at the 500 meter scale. As the distance to escape terrain increased mountain goats were less likely to occupy treed areas. The ruggedness index used in my presence-only modeling effort was based on the rate of change in slope. By using a ruggedness index which included changes in slope and aspect I improved model performance. This research demonstrates the feasibility of conducting occupancy surveys in mountainous terrain and provides interesting biological insights regarding mountain goats and their habitat.Item The influence of riparian-canopy structure and coverage on the breeding distribution of the southwestern willow flycatcher(Montana State University - Bozeman, College of Letters & Science, 2005) Brodhead, Katherine May; Chairperson, Graduate Committee: Richard J. AspinallThere is a long history of relating bird species diversity and distributions to heterogeneity in foliage structure as seen from within the habitat and measured from the ground up. There is also an overwhelming contribution in the literature promoting and justifying a broad-scale approach to characterizing spatial patterns, especially for the purpose of relating to, and predicting, species distributions. This study draws from the relationship between birds and habitat structure but assesses heterogeneity in structure from a broader perspective. For this analysis, I compared the spatial distribution of a breeding population of the southwestern willow flycatcher (Empidonax extimus traillii) to the structure of a riparian zone with an emphasis on capturing patterns that are measured horizontally across the zone. Riparian zones are dynamic by nature and are structurally diverse in a natural, healthy system, and support a high density of breeding birds. The flycatcher prefers dense riparian habitat in close proximity to lentic water. The structural characteristics of the riparian zone where dense vegetation and water are present were hypothesized to be more structurally heterogeneous and to support a broader riparian zone. Riparian zone structure was mapped and stand characteristics were extracted, with the intent of relating spatial patterns in stand heterogeneity and riparian extent to the spatial distribution of the southwestern willow flycatcher. A moving window function in a GIS assessed the stand characteristics, which were imported as attributes to presence/absence data points. The extent of the analysis window was varied to determine the scale at which the habitat characteristics were most highly correlated with flycatcher presence. Correlation between the structural characteristics of the stand and the presence/absence of the flycatcher was modeled with logistic regression. Results show the flycatcher is more likely to occupy habitat that is structurally heterogeneous and has more riparian vegetation. The results also show that selection is most sensitive to habitat characteristics within a relatively close proximity.