Hummingbird Foraging Preference: The Hierarchical Impacts of Color, Position, and Concentration on Visitation Frequency

Hummingbirds are well adapted to efficiently locate high quality nectar sources, but relatively few studies have examined the mechanisms of that process under natural conditions in the field. This study investigates the visual signals that allow hummingbirds to do just that, as well as the external factors that limit their choices in foraging. More specifically, feeder color and nectar concentration were manipulated to determine the effect of those independent variables on visitation frequency. An initial experiment was conducted in order to explore color preference among the visiting species. Red, orange, and blue feeders were filled with nectar of equal concentrations and the feeders were rotated three times to ensure each color was observed in each position. Once preference was established, a second experiment was conducted in which the feeder of least preferred color, blue, was placed in the least preferred position and filled with a higher nectar concentration, while two red feeders remained at the initial concentration. Eight hours of observation were completed each day, with the following data collected for each foraging bout: feeder color and position, species and sex of visiting individual, time of arrival, number of visits, and behavioral notes. Territoriality played a major role in determining visitation to each feeder, with first a male violet-tailed sylph and then a brown Inca asserting their role as dominant territorialists that chased indiscriminately. It was discovered that, when nectar reward was equal for each feeder, position was the primary factor in determining visitation frequency. However, visitation to each position was influenced by feeder color, each position receiving the most visits when the red feeder was in place. During the second experiment, no clear preference for the higher concentration was shown by the end of the four days, but visitation to that feeder exhibited an upward trajectory and increased consistently each day, which suggests that preference would eventually be indicated. The findings of this investigation indicate the presence of a hierarchy of factors impacting feeder choice, pointing to nectar concentration with the strongest influence, followed by position and then color. \ Los colibríes están bien adaptados para poder encontrar fuentes de azúcar en una manera muy eficiente, pero pocos estudios han investigado los mecanismos por los que funciona ese proceso bajo condiciones naturales fuera de un laboratorio. Esta investigación examina las señales visuales que permiten que los colibríes hagan exactamente eso, además los factores externos que limitan sus opciones en el forrajeo. El color de bebedero y la concentración del néctar fueron manipulados para averiguar cómo afectan esos variables independientes a la frecuencia visitación. Un experimento inicial se realizó con el propósito de explorar la preferencia del color entre los colibríes visitantes. Tres bebederos de rojo, naranjo, y azul se llenaron de néctar de concentraciones iguales y lo