Physiological Correlates of Preference and Aversion for Sugars in Three Species of Birds

• Published in: Physiological zoology 1988-05, Vol.61 (3), p.222-229
• Main Authors: del Rio, Carlos Martinez, Stevens, Bruce R., Daneke, Dennis E., Andreadis, Paul T.
• Format: Article
• Language: English
• Subjects: Animals; Aves; Biological and medical sciences; Birds; Blood glucose; Carbohydrates; Diet; Enzymes; Fruits; Fundamental and applied biological sciences. Psychology; Metabolisms and neurohumoral controls; Monosaccharides; Reagents; Starlings; Sugars; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0031-935X; 1937-4267
• DOI: 10.1086/physzool.61.3.30161235

We studied preferences of red-winged blackbirds, common grackles, and European starlings for the disaccharide sucrose and the monosaccharides glucose and fructose. We also tested the hypothesis that sucrose preference is correlated with activity of sucrase, the intestinal enzyme that hydrolyzes sucrose. All species preferred a 1:1 mixture of glucose and fructose over water at concentrations > 0.75 M. Starlings rejected concentrated solutions of sucrose and lacked sucrase activity. Red-winged blackbirds preferred sucrose solutions at intermediate concentrations (0.35 M) but rejected concentrated ones, whereas common grackles preferred sucrose at all the concentrations offered. Sucrase activity was higher in grackles than in red-winged blackbirds. Blood glucose levels were measured after a meal of a mixture of glucose and fructose or of sucrose. Blood glucose concentration increased in all species after the monosaccharide meal and peaked after about 30 min. In starlings the concentration of glucose in blood remained constant after a sucrose meal, whereas in the other species there was an increase similar to that observed after a monosaccharide meal. Because starlings are mainly insectivorous and blackbirds and grackles are granivorous, we hypothesize that relative activity of intestinal sucrase and hence the preference for sucrose are related to the proportion of complex carbohydrates in a bird's diet.