2023 67 B3

Which Biotic and Abiotic Factors Influence Dominance and Vagrancy in Hummingbird Communities?

By: Elizabeth Mathiasen, Dikshita Germilla, Sierra Ekmalian, Jesus Ovalle

Department: Biology

Faculty Advisors: Dr. Derrick Groom, Dr. Lisa Tell (UC Davis)

Dynamics of dominance hierarchies in hummingbird communities are complex and can rapidly change over short time scales. These changes are shaped by a variety of factors, including phenotypic traits, community composition (species and bird population at feeders), and environmental factors. We seek to explore what factors are related to changes in dominance over time, and how feeder displacement affects visitation at nearby feeders. We hypothesize that sex, age, plumage characteristics, and season will impact feeder dominance and vagrancy, with older and more male-like birds being more feeder dominant. We also hypothesize that an individual’s displacement from one feeder will impact adjacent feeder visits. From 2016 to 2021, three species of hummingbirds (Calypte anna, Selaphorus sasin, and Archilochus alexandri) were tagged with passive integrated transponders at two sites in California and feeders were equipped with tag-readers. At time of capture, each bird was identified by species, sex, and age, and the proportion of plumage iridescence was scored. Dominant individuals were determined by the proportion of total visits to each feeder by each bird, with those not meeting the threshold considered vagrant. Preliminary results suggest that dominant birds have a higher proportion of iridescent feathers than more vagrant individuals; dominance in both male and female Anna’s Hummingbirds (C. anna) was related to gorget iridescence. Increased gorget iridescence in female birds may provide a competitive advantage by causing them to appear more male-like. Further work using this novel approach will examine additional factors that may influence dominance at feeders.