DOI
https://doi.org/10.25772/08R5-8254
Defense Date
2025
Document Type
Thesis
Degree Name
Master of Science
Department
Environmental Studies
First Advisor
Dr. Lesley Bulluck
Abstract
Abstract Shrubland and early successional habitats (ESH) support a diversity of wildlife, including many declining songbirds. However, nonnative shrubs increasingly dominate these habitats, potentially altering habitat quality by influencing prey availability. Habitat quality can be assessed by observing foraging behaviors of songbirds and identifying preferred and avoided substrates as well as testing the predictions of optimal foraging theory; specifically that birds will maximize their energy gain relative to the costs. We examined foraging behaviors of Golden-winged Warblers (Vermivora chrysoptera; GWWA) and Chestnut-sided Warblers (Setophaga pensylvanica; CSWA) in ESH on private lands in Virginia with varying amounts of nonnative shrub cover. Using foraging observations, we assessed substrate preference and avoidance, and whether foraging behaviors (attack rate, movement rate, and search effort) vary with the substrate they are foraging on and/or the broader context (i.e., the amount of nonnative shrub cover in the area). Both warbler species prefer to forage on native plants while disproportionately avoiding nonnative. Black locust (Robinia pseudoacacia), hawthorn (Crataegus spp.), and cherry (Prunus spp.) were the most preferred foraging substrates. GWWA had higher movement rates when foraging on avoided substrates, while CSWA had higher attack rates on preferred substrates. These substrate-level results support the predictions of optimal foraging theory, which assumes preferred substrates have higher prey availability than avoided substrates. However, when considering the broader vegetative context of foraging birds, behaviors did not follow expected patterns based on optimal foraging theory. Our findings demonstrate that these warblers have a strong preference for foraging on native plants and avoiding nonnative plants, and that preferred substrates likely have higher prey availability. Still, it is not clear if prey availability on preferred substrates is reduced when surrounded by nonnative plants. In this study, foraging observations occurred where the percentage of nonnative shrubs was always < 40% of all available substrates and it may be that habitat quality is only negatively impacted when nonnative shrubs comprise ≥50% of available foraging substrates. We recommend that this research be used to guide private land management and restoration efforts in Virginia working landscapes by promoting native vegetation planting, retaining diverse early successional habitat, and reducing the spread of nonnative plant species to enhance habitat quality for shrubland birds.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-9-2025