Effects of urbanization on the relative abundance of hummingbirds (Archilochus alexandri and Archilochus colubris) as measured by resource removal rates
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Urbanization has led to a loss of natural habitat, an increase in impervious surfaces, and subsequently, an increase in the provisioning of food sources for local wildlife. One common scenario of supplementary feeding includes artificial nectar feeders for hummingbirds, which can be so successful at attracting hummingbirds as to cause an increase in local abundance past natural carrying capacity. While previous studies have investigated persistence of hummingbird populations across an urban-rural gradient, mine is the first to use sucrose removal from hummingbird feeders as a proxy variable for relative hummingbird abundance. I deployed nectar feeders (N=27) in locations encompassing various intensities of imperviousness (i.e. percent of impervious surfaces, which is an indicator of urbanization intensity) and canopy cover around San Marcos, Texas, USA, to determine whether these factors affect the relative abundance of Archilochus alexandri and Archilochus colubris within 100, 200, and 400 m spatial scales. Extraneous variables including Julian date, resource availability, precipitation, and temperature were considered, but ultimately none of these individually had an effect on solution consumption (P>0.05). Imperviousness had a negative significant effect on solution consumption across all three spatial scales, indicating that hummingbirds are less abundant in areas of greater urban development (P≤0.05). Canopy cover had a non-significant effect on solution consumption at all spatial extents (P>0.1). In addition to developing a reliable new method for surveying hummingbirds, my findings show that urbanization, despite warmer local temperatures and increased food provisioning, may negatively affect some hummingbird populations.