Taste Preferences, Color Preferences, and Flower Choice in Hummingbirds

F. Gary Stiles
1976 The Condor  
Taste and color preferences have been experimentally demonstrated for a variety of birds, and the literature on food habits of wild birds is enormous, but as yet there is little to tie the two together. Laboratory experiments have usually involved taste stimuli that are probably irrelevant to birds in the wild; and the taste stimuli presented by insects, seeds, fruit, etc. are complex and difficult to duplicate for experimental purposes. The same is true to a considerable extent of color: the
more » ... ent of color: the mostly granivorous species studied so far probably never experience bright, monochromatic colors in connection with feeding. Moreover, caloric parameters of birds' foods are often difficult to measure or estimate but will almost certainly affect food selection, making taste and color preferences harder to assess. Hummingbirds are ideal subjects in studies of taste and color preferences. Their main foods are nectar and insects; flowers are visited almost exclusively for nectar, insects being captured elsewhere. Flower nectar is essentially an aqueous solution of 3 common sugars (Percival 1961, see also beyond). It can be easily sampled and its concentration, caloric value, and composition measured. The taste stimuli can be readily duplicated and manipulated experimentally. Assimilation of flower nectar is essentially 100% (Hainsworth 1974) making caloric parameters easy to estimate. Flowers visited by hummingbirds are usually brightly colored and fairly unpatterned, also favoring experimentation. The long controversy over the existence of color preferences in hummingbirds was reviewed by Grant and Grant ( 1968). The roles of color and taste factors have been greatly clarified by the feeding station experiments of Collias and Collias (1968); similar experiments by Miller and Miller (1971) further elucidated the role of position. These studies suggest a hierarchy of factors influencing feeder choice: sugar concentration and/or taste over position over color. As yet this hierarchy has not been subjected to experimental verification, or applied in detail to flower choice in the field. This paper presents laboratory experiments on taste and color preferences of the Anna Hummingbird (Calypte anna) and several other species. I also present the results of extensive field observations on flower choice by hummingbirds, and consider the taste and color stimuli presented by those flowers visited by hummingbirds. Hopefully, comparing the results of field and laboratory studies will permit a more realistic evaluation of the role of taste and color preferences in food choice by hummingbirds, and a better understanding of the coevolution of hummingbirds and the flowers they pollinate. LABORATORY EXPERIMENTS ON TASTE AND COLOR PREFERENCES The laboratory experiments reported here were carried out at the University of California, Los Angeles, between spring 1966 and fall 1969. Hummingbirds were captured with mist nets, either at wild or cultivated flowers, or at feeding stations. They were transferred to the laboratory in a carrying case as described by Lasiewski ( 1962). When not being used in experiments, birds were housed in groups of 4 to 8 in holding cages 50 x 50 x 100 cm in size. In general, a large number of birds and a small number of feeders prevented domination of the feeders by one or two birds, and insured that birds low in the cage dominance hierarchy were able to feed. The experimental cage was cubical, 50 cm on a side, containing a central perch and 2 to 4 feeders, depending on the experiment. The cages were designed to minimize position variables by placing the feeders close together and equidistant from the perch. The feeders were inverted 25-or 50-ml polystyrene graduated cylinders with a glass tube and rubber cork inserted in the open end. Cages were lighted by fluorescent lamps emitting light of approximately the same spectral composition as sunlight. The birds were kept on a 12-hr photoperiod in a windowless room; temperature fluctuated between 17 and 22°C. The sugars used in all experiments were sucrose, glucose, and fructose, and various mixtures thereof; these sugars are the main constituents of flower nectars (Percival 1961). Sugar solutions were made up on a weight sugar per volume solution basis, with concentrations expressed as percentages (e.g. 30% = 30 g sugar in 100 ml solution). Percentage, rather than molarity, was used because the disaccharide sucrose has a molecular weight approximately twice that of the monosaccharides glucose and fructose, but the number of calories per gram is nearly the same for all 3 sugars. For color preference experiments, colored disks approximately 2 cm in diameter were affixed to the mouths of the feeder tubes. The colors used were made up by mixing acrylic paints to obtain as nearly equal brightness as possible. Brightness was assessed as percentage of incident light reflected at the wavelength of maximum reflectance, by a Beckman G2 spectrophotometer fitted with a reflectance unit (see Porter 1967, for a detailed description of 1101
doi:10.2307/1366912 fatcat:d5sc4lt6qbci7mnvkjhlph6lti