Effects of non-native woody plant species on shrubland birds of conservation concern

Shrubland birds are among the fastest declining groups of birds over the past 50 years. Habitat loss and degradation are proposed as being major drivers, but the underlying causes of these declines are unknown. I investigated some of the potential factors driving population declines in three species listed by the Illinois Department of Natural Resources as Species in Greatest Need of Conservation (Bell’s Vireo (Vireo bellii bellii), Yellow-breasted Chat (Icteria virens), and Field Sparrow (Spizella pusilla)). I visited 112 shrubland sites across Illinois to gather information on the bird and vegetation community over a three-year period. I looked at how habitat characteristics at different scales of habitat selection influenced birds’ occupancy dynamics, as well as how the three most abundant non-native shrub in Illinois (autumn olive (Elaeagnus umbellata), honeysuckle (Lonicera spp.) and multiflora rose (Rosa multiflora)), influenced birds’ physiological health and condition. I found that non-native plant species, specifically multiflora rose, negatively associated with shrubland bird occupancy dynamics, especially for Bell’s Vireo and Yellow-breasted Chat. Field Sparrows were found on nearly all shrubland sites I surveyed, and appeared to utilize shrublands regardless of their composition or context on the landscape. Additionally, I found that autumn olive, honeysuckle and native plant species had a relationship with the stress (corticosterone), diet quality (triglyceride and β-hydroxybutyrate), and immune function (bacteria-killing ability) of all three species. Bell’s Vireos had higher corticosterone concentrations in relation to increasing prevalence of autumn olive. Yellow-breasted Chats and Field Sparrows had lower triglyceride concentrations in relation to increasing prevalence of honeysuckle, and all three species had decreasing concentrations of β-hydroxybutyrate in relation to honeysuckle as well. Finally, increasing percentages of native plant species had a positive influence on bacteria killing-ability of the three shrubland obligate species. My results suggest that increasing the number of shrubland habitats in combination with the replacement of non-native woody shrubs with native plants would benefit these three shrubland obligate birds