Use of Food Resources by White-winged Doves and Great-tailed Grackles at Urban Bird Feeders in Central Texas with Observations on Columbid Wing Raising Behavior
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As White-winged Doves and Great-tailed Grackles have expanded their range northward, these species have shown an increased affinity for urban areas with a constant supply of anthropogenic food sources. I compared usage of bird feeders by both of these species with more-established avian species in urban central Texas. I set up 15 feeding stations in San Marcos and 15 in San Antonio. I digitally recorded interaction events for half-hour intervals in summer 2009 and winter 2010. I used recordings to calculate total time spent by each species at each feeding station, count the number of aggressive interactions, and determine participants in each interaction. I also recorded instances of White-winged Doves raising their wings in a threat display, noting which wing was used to signal. In summer, both White-winged Doves and Great-tailed Grackles used feeding stations the most, with the exception of Mourning Doves. In winter, there was little difference between feeding station usage by White-winged Doves and Great-tailed Grackles; however House Sparrows used feeding stations more than either species. White-winged Doves were displaced by other species during summer, but became more aggressive in winter, perhaps to obtain more limited resources. Further studies are needed to determine if these range expansions are negatively affecting more-established avian species. White-winged Doves raised the wing opposite their opponent most of the time rather than the wing on the same side, as would be expected for wing-slapping. This is consistent with other dove species and appears to be an expression of conflicting choices to flee an aggressor or stay at the feeding station. The White-winged Doves’ white wing-bars may play a role in signal amplification of this behavior, but further research is needed to confirm this.