Date of Award


Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)


Biological Sciences

First Advisor

Robert B. Frederick

Department Affiliation

Biological Sciences


The trumpeter swan (Cygnus buccinator) has historically nested in the Greater Yellowstone Ecosystem of Montana, Idaho, and Wyoming. Declines in habitat quality may be limiting the growth of the Tri-State Flock. The purpose of this study was to map historical nesting areas for trumpeter swans in Yellowstone National Park (YNP) and evaluate Landsat images for changes to habitat. Historical nesting sites were evaluated through image classification and Normalized Difference Vegetation Index (NDVI) and compared to field conditions. Swan nesting records were analyzed in comparison to drought index and human visitation rates to determine if these factors may contribute to the decline of trumpeter swans nesting in YNP.

Vegetation type and water quality were evaluated at 36 wetlands identified as historical nesting locations. Potamogetonaceae was the largest family represented in plant samples and had the highest frequency of occurrence in samples. There was no significant difference in whether swans were present or absent in wetlands with regards to water quality parameters tested or physical parameters identified. There was an association between certain drought index values and the number of cygnets fledged and the number of territories occupied by swan pairs.

I was unsuccessful in using image classification to define pixel characteristics common among historical nesting territories of swans in YNP based on 5 Landsat images from 1975, 1979, 1990, 1999, and 2005. I was also unable to distinguish aquatic plant species composition, emergent and submergent plants, open water versus aquatic vegetation, wetland classification, or swan preference using image classification. No relationship was found in a regression model of NDVI values and swan pair occupancy or number of swans fledged, with the exception of a weak, positive relationship between pair occupancy and positive NDVI values, and a strong, positive relationship between swan fledge rates and positive NDVI values derived from the 1990 image. Landsat images currently appear to be unreliable in predicting swan pair occupancy or fledging success of nesting pairs. NDVI calculations were not consistently reliable in predicting relationships with swan pair presence or fledge success in nesting territories of YNP, but significant relationships did indicate that factors which might influence swan pair occupancy and fledge rates may be monitored through continued use of NDVI calculations.

There was a significant curvilinear relationship between human visitation rate and the number of territories occupied by pairs of swans, the number of territories that fledged cygnets, and the number cygnets fledged, which was particularly evident in years with high visitation rates and poor swan productivity. There was no significant difference in the number of swans fledged in areas near park trails or near park roads compared to more remote locations, and swan fledging was independent of proximity to remote or visitor-accessible areas.

A goal of this study was to provide park managers with a method for assessing habitat quality that might be used to monitor nesting trumpeter swans in YNP. Image classification of nesting wetlands did not provide a useful model of areas suitable for nesting trumpeter swans, but NDVI classification has the potential to provide information useful in long-term monitoring of factors which may influence swan nesting. While no overall trends were observed through Landsat modeling, continued analysis could provide information to park managers in terms of the quality of individual nesting sites and changes over time. Climate change predictions and human visitation impacts can be incorporated to provide managers with the information they need to make decisions regarding the future of nesting trumpeter swans in YNP.