Impacts of elk management and riparian condition on songbirds in Rocky Mountain National Park
Date
2015
Authors
Craig, Apryle Dawn, author
Pejchar, Liba, advisor
Aldridge, Cameron, committee member
Noon, Barry, committee member
Bobowski, Ben, committee member
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Abstract
The widespread loss of apex predators from the western U.S. is having cascading effects on ecosystems. As in other western parks, riparian willow (Salix spp.) communities in Rocky Mountain National Park (RMNP) are declining as a result of a trophic cascade involving the local extinction of wolves (Canis lupus) and an exponential increase in elk (Cervus elaphus). In 2008, RMNP began installing elk exclosures to protect and restore willow communities and the diverse taxa that depend on riparian ecosystems from heavy browsing. Using point counts, I evaluated the effect of elk exclosures and riparian shrub condition on songbird density and occupancy. I found little support for a direct effect of elk exclosures on bird communities, with the exception of shrub nesting birds which occurred at higher densities within exclosures. However, the density and occupancy of some riparian bird species and guilds was positively correlated with particular vegetation conditions in this ecosystem. Shrub height positively related to both density and occupancy of Dusky Flycatcher. For the Lincoln Sparrow and shrub-nesting guild, occupancy also had a positive relationship with shrub height. The percent of shrub cover within 15 m of the survey point was an important positive predictor of density for Lincoln's Sparrows, Song Sparrows, and Wilson's Warblers, and foliage-gleaner and shrub-nesting guilds. The percent of riparian shrub cover within 300 m was an important positive predictor for the density of Wilson's Warblers. American Robin, a habitat generalist, and ground-nesting and foraging guilds did not respond strongly to shrub cover or height at any scale. These results reflect the variable shrub conditions inside and outside exclosures, and affirm that managing for mid to high density shrub cover and height will be beneficial for some riparian specialists. My findings provide park managers critical information on bird communities in experimental elk exclosures, and insight into the conditions needed to support songbird communities in the park's riparian ecosystems.
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Subject
exclosures
riparian buffer
willow
herbivory
birds
trophic cascades