Theses and Dissertations at Montana State University (MSU)
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Item Retrospective analysis of a declining trumpeter swan (Cygnus buccinator) population in Yellowstone National Park(Montana State University - Bozeman, College of Letters & Science, 2021) Shields, Evan Michael; Chairperson, Graduate Committee: Jay J. RotellaBy 1933, the number of trumpeter swans (Cygnus buccinator) in the continental United States was reduced to roughly 70 individuals that nested and wintered in Yellowstone National Park (YNP) and the surrounding Greater Yellowstone area. While conservation measures saved the trumpeter swan, and their numbers have increased greatly across North America, abundance and productivity of YNP's resident trumpeter swan population declined from the 1960's through about 2010. Many hypotheses for the initial decline in YNP trumpeter swans exist, including human disturbance at nesting areas, changes in habitat quality, predation, and management of trumpeter swans outside of YNP. To improve knowledge and take advantage of long-term monitoring of trumpeter swans, this retrospective study was designed to evaluate the various competing hypotheses about possible factors associated with temporal and spatial variation in swan abundance and reproductive success in YNP for 1931-2019. Two different types of analyses were used: (1) analysis of annual park-wide counts of trumpeter swan territories with swans Absent, Present but unsuccessful (Present), and Successful, and (2) Bayesian reversible jump Markov chain Monte Carlo analysis that evaluated the utility of covariates representing swan decline hypotheses for explaining variation in annual, territory-level patterns of where swans were Absent, Present, and Successful each year. My results provide novel information on temporal patterns in the annual number of Absent, Present, and Successful territories, and analysis of covariates that are useful to explain variation in territory statuses identified several interesting covariate relationships. Swan territories within YNP were more likely to have trumpeter swans Present as opposed to Absent during 1931-2011 in years when total abundance of trumpeter swans in the broader geographic area around YNP was greater. Because several covariates have values that trend through time, it is difficult to distinguish between several alternative interpretations for the underlying causes of temporal trends. Identification of swan territories most likely to have swans Present and Successful can be a useful tool to help YNP staff manage important swan habitat or justify targeted management actions. Future work that utilizes satellite imagery to reconstruct lake/wetland hydrology is likely to be useful to describe potential changes in habitat quality.Item Occupancy modeling of non-native mountain goats in the greater Yellowstone area(Montana State University - Bozeman, College of Letters & Science, 2015) DeVoe, Jesse Daniel; Chairperson, Graduate Committee: Robert A. GarrottNon-native species can have adverse impacts on native species; however, coexistence may be possible if their ecological niches minimally overlap. Fine spatial scale information is needed to understand these niches but can be challenging to obtain for rare, imperfectly detected species inhabiting difficult to survey landscapes. Non-native mountain goats (Oreamnos americanus) in the greater Yellowstone area (GYA) are such a species and have substantial potential to expand in distribution and occupy similar habitats to native Rocky Mountain bighorn sheep (Ovis canadensis canadensis). To understand the niche and potential for expansion of mountain goats in the GYA, this study used a unique, fine spatial scale method to collect detection-nondetection data from two study areas with established mountain goat populations over three summer seasons (2011-2013). Relationships between scale-specific habitat covariates and mountain goat selection were evaluated using a single-species, single-season occupancy analysis to model occupancy and detection probabilities based on 505 mountain goat detections from 53,098 surveyed sampling units. Habitat selection was most strongly associated with terrain covariates, including mean slope and slope variance, at a spatial scale of 500 x 500 m, and canopy cover, heat load, and normalized difference vegetation index at a spatial scale of 100 x 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 superior terrain covariates to distance to escape terrain that has dominated published mountain goat habitat models. The model predicted 10,745 km2 of suitable habitat within the GYA, of which 57% is currently un-colonized. Throughout the GYA, suitable habitat appears to generally overlap extensively with areas occupied by bighorn sheep. I also estimated the GYA may have the potential to support 5,372-8,918 mountain goats when all predicted habitat is occupied, or approximately 2.5-4.2 times the most recent abundance estimate of 2,104.