Witmer M C
Section of Ecology and Systematics, Cornell University, Ithaca, New York 14853, USA.
Physiol Zool. 1998 Nov-Dec;71(6):599-610. doi: 10.1086/516001.
To assess how the high-sugar/low-protein content of fruit diets affects digestive function and nutrition of frugivorous birds, I compared intake, passage rate, sugar utilization, protein requirements, and mass changes of cedar waxwings (Bombycilla cedrorum), American robins (Turdus migratorius), and wood thrushes (Hylocichla mustelina) fed synthetic diets simulating the range of sugar (6.6%, 12.4%, and 22.0% solutes) and protein (4.5%, 3.0%, and 1.5% of dry matter) content of bird-dispersed fruits. The dietary emphasis on sugary fruits by cedar waxwings suggests the potential for digestive and physiological specializations to this food type. All birds increased volumetric food intake and passage rates as sugar concentration declined. Birds completely (22.0%-12.4% sugar solute concentration) or incompletely (12.4%-6.6% sugar solute concentration) compensated for dietary dilution. Cedar waxwings consumed each diet at higher rates than did thrushes, as they do when eating sugary fruits, demonstrating that interspecific differences in ingestion rates of sugary fruits are a consequence of nutrient composition, rather than seed bulk or secondary compounds of fruits. Passage rate was not responsible for interspecific differences in short-term food intake rate, implicating gut morphology as the key functional feature limiting intake. Most sugary fruits are nutritionally deficient in apparent protein for thrushes but are nutritionally adequate in protein for cedar waxwings because of this species' relatively high intake rates and low protein requirements. The digestive systems of frugivorous birds respond flexibly to dietary sugar concentration, but protein content of fruits can present a nutritional limitation, potentially influencing the proportions of fruit and animal foods in birds' diets.
为了评估水果饮食中高糖/低蛋白含量如何影响食果鸟类的消化功能和营养状况，我比较了以模拟鸟类传播果实中糖（溶质6.6%、12.4%和22.0%）和蛋白质（干物质的4.5%、3.0%和1.5%）含量范围的合成饲料喂养的雪松太平鸟（Bombycilla cedrorum）、美洲知更鸟（Turdus migratorius）和伍德 Thrush（Hylocichla mustelina）的摄入量、通过率、糖利用率、蛋白质需求和体重变化。雪松太平鸟对含糖果实的饮食偏好表明其对这种食物类型具有消化和生理特化的潜力。随着糖浓度的下降，所有鸟类的食物摄入量和通过率都增加了。鸟类完全（糖溶质浓度从22.0%降至12.4%）或部分（糖溶质浓度从12.4%降至6.6%）补偿了饮食稀释。雪松太平鸟食用每种饲料的速率都高于画眉，就像它们吃含糖果实一样，这表明含糖果实摄入速率的种间差异是营养成分的结果，而不是果实的种子大小或次生化合物。通过率不是短期食物摄入速率种间差异的原因，这表明肠道形态是限制摄入量的关键功能特征。大多数含糖果实对画眉来说蛋白质营养不足，但对雪松太平鸟来说蛋白质营养充足，因为该物种的摄入量相对较高且蛋白质需求较低。食果鸟类的消化系统对饮食中的糖浓度有灵活的反应，但果实中的蛋白质含量可能会造成营养限制，潜在地影响鸟类饮食中果实和动物性食物的比例。
