Does Branch Structure of an Invasive Shrub (Elaeagnus umbellata) Alter Bird Perching Behavior?

Autumn Olive, Elaeagnus umbellata, has been introduced throughout the United States. Research on the impacts of invasive plants like E. umbellata on bird behavior has produced conflicting results with some birds preferring to use invasives while others avoid them. Branch structure has been implicated in bird preference for certain woody species. Thus, we asked the question, does E. umbellata differ in branch structure from common natives in the landscape and, if so, how does this difference impact the behavior of native birds? We examined this question during the non-fruiting season at study sites with mixed open and shrubby second growth forest habitats in Michigan and Indiana. We found that E. umbellata branches were twice as dense and 45% smaller in diameter than those of native cherry, Prunus serotina, but did not differ from two other native shrubs. Birds did not show a preference for perching in native shrub branches in choice tests using bird feeders in situ with invasive or native branches. Mist net capture rates for birds also did not differ between E. umbellata and native shrub sites. We concluded that native birds do not avoid E. umbellata during the non-fruiting season for perching despite a unique branch structure

Restoring major ecosystem drivers in one of the world's most endangered ecosystems : the effects of bison reintroduction, prescribed fire, and time since restoration on grassland bird nest success in tallgrass prairie

Advisors: Holly P. Jones.Committee members: Nicholas A. Barber; Christopher J. Whelan.Tallgrass prairie has been converted to agriculture over the past century, making it one of the most threatened ecosystems globally. Agriculture conversion of prairie has severely fragmented the landscape and many grassland birds are now in decline and threatened with regional extirpation. Restoration projects have sought to increase the quality and size of prairie fragments by converting cultivated land back to prairie through revegetation and management with prescribed fire, hypothetically increasing breeding habitat for grassland birds. Bison and other native grazers are now being reintroduced to prairie restorations as a final step in a complete restoration to increase habitat quality. The goal of this study was to understand how restoration practices influence nest density and survivorship. I hypothesized that nest density and survivorship would increase with restoration age, fire return interval, and bison presence. I measured nest density and survivorship and deployed artificial nests in four restored tracts and two remnant tracts from May to July 2014 and 2015. Nest density of natural nests decreased following bison reintroduction. These results suggest that bison do not have an immediate impact on grassland bird survivorship. Future research, however, is needed to see if these patterns hold over time and if they are affecting species composition or nest success alone.M.S. (Master of Science

Branch Morphology of Nonnative Elaeagnus Shrubs and Potential Consequences for Avian Activity in Midwestern Habitats

Invasive nonnative species of woody plants can alter landscapes in ways that are detrimental to native wildlife. We studied branch structure of invasive nonnative Elaeagnus shrubs (autumn and Russian olive E. umbellata and E. angustifolia) as a potential influence on native bird activity in Midwestern habitats. In a comparison to three common native woody plants, Elaeagnus shrubs had a finer branch and denser structure than native black cherry (Prunus serotina) but did not differ from natives in other characteristics tested. Further, the morphological characteristics of Elaeagnusbranches did not appear to affect preference for perching substrate at feeders or activity of birds moving through Elaeagnus and native shrub areas monitored using mist nets. Thus, we concluded that any morphological changes that may occur when Elaeagnus shrubs invade a habitat would not negatively impact overwintering and breeding bird perching behavior or movements during the nonfruiting season

Assessing changes to ecosystem structure and function following invasion by Spartina alterniflora and Phragmites australis: a meta-analysis [Supplemental Files]

Includes data and R codeBiological invasions resulting from anthropogenic activities are one of the greatest threats to maintaining ecosystem functioning and native biodiversity. Invasions are especially problematic when the invading species behaves as an ecosystem engineer that is capable of transforming ecosystem structure, function, and community dynamics. Of particular concern is the spread of emergent wetland grasses whose root systems alter hydrology and structural stability of soils, modify ecosystem functions, and change community dynamics and species richness. To address the threats posed to ecosystems across the globe, management practices focus on the control and removal of invasive grasses. However, it remains unclear how severely invasive grasses alter ecosystem functions and whether alterations persist after invasive grass removal, limiting our ability to determine if management practices are truly sufficient to fully restore ecosystems. Here, we conducted a meta-analysis to quantify ecological alterations and the efficacy of management following the invasion of Spartina alterniflora and Phragmites australis, two common and pervasive invaders in coastal wetlands. Our results indicate that S. alterniflora and P. australis significantly alter measures of ecosystem functioning and organismal abundance. Invaded ecosystems had significant elevations in abiotic carbon and nitrogen fixation and uptake in areas with invasive grasses, with differential photosynthetic pathways of these two grass species further explaining carbon fluxes. Moreover, evidence from our analyses indicates that management practices may not adequately promote recovery from invasion, but more data are needed to fully assess management efficacy. We call for future studies to conduct pairwise comparisons between uninvaded, invaded, and managed systems and provide research priorities