PARENT SESSION
Oral Session #64: Avian Ecology. Presiding: P. Warren.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas I.
Phenotypic flexibility in the digestive system of goslings: implications for geese in poor quality habitat.
McWilliams, Scott1, Karasov, William2, Leafloor, James2, Caviedes-Vidal, Enrique3, 1 2 3
ABSTRACT- When habitat quality on the breeding grounds is poor, arctic-nesting geese must eat foods of lower quality than their preferred foods. We tested the hypothesis that when goslings eat foods of lower quality, (a) they eat more, (b) their digesta retention time and digestive efficiency does not change, (c) their total capacity for breakdown and absorption of nutrients increases, and (d) the mechanism responsible for the increase in total capacity will be an increase in amount of intestine rather than an increase in intestinal tissue-specific enzyme activity or nutrient transporter activity. We measured food intake, gut anatomy, retention time of digesta, enzyme hydrolysis rates, and digestive efficiency in Canada and Snow goose goslings raised on grass-based diets that differed in fiber content (30% or 50%) and protein content (10%, 14%, or 18%). Goslings fed lower quality food (50% fiber) ate more, retention time of digesta and tissue-specific enzyme activity did not change with diet, and digestive efficiency was only slighter lower for high-fiber diets (58% AME) compared to low-fiber diets (65% AME). Gizzard and small intestine mass increased with food intake so that the total capacity for breakdown and absorption of nutrients increased in goslings fed lower quality diets. However, this phenotypic flexibility in digestive physiology only partially compensated for the reduction in diet quality as indicated by slower growth and poorer survival of goslings fed the high-fiber, low-protein diets.
KEY WORDS: Digestion in birds, diet quality, Branta canadensis, Anser caerulescens caerulescens