Romanek C S, Gaines K F, Bryan A L, Brisbin I L
Savannah River Ecology Laboratory, Drawer E, Aiken, SC 29802, USA, USA.
Department of Geology, University of Georgia, Athens, GA 30602, USA, USA.
Oecologia. 2000 Dec;125(4):584-594. doi: 10.1007/s004420000471. Epub 2000 Dec 1.
Down feathers and regurgitant were collected from nestling wood storks (Mycteria americana) from two inland and two coastal breeding colonies in Georgia. The stable isotopic ratios of carbon (C/C) and nitrogen (N/N) in these materials were analyzed to gain insights into the natal origins of juvenile storks and the foraging activities of adults. Down feathers differed in δC between inland and coastal colonies, having average isotopic values that reflected the sources of carbon fixed in biomass at the base of the food web. Feathers from the inland colonies differed between colonies in δN, while those from the coastal colonies did not. These patterns primarily reflected the foraging activities of parent storks, with individuals capturing differing percentages of prey of distinct trophic status at each colony. Collectively, the carbon and nitrogen isotopic signatures of feather keratin were used to distinguish nestlings from each colony, except for instances where storks from different colonies foraged in common wetlands. The stable isotopic composition of food items in regurgitant was used to reconstruct the trophic structure of the ecosystems in which wood storks foraged. Predicted foraging activities based on the isotopic composition of keratin were generally consistent with the percentage of prey types (freshwater vs. saltwater and lower trophic level vs. upper trophic level consumer) observed in regurgitant, except for the coastal colony at St. Simons Island, where the δC of feathers strongly suggested that freshwater prey were a significant component of the diet. This inconsistency was resolved by aerial tracking of adults during foraging excursions using a fixed-wing aircraft. Observed foraging activities supported interpretations based on the stable isotope content of feathers, suggesting that the latter provided a better record of overall foraging activity than regurgitant analysis alone. Observed foraging patterns were compared to the predictions of a statistical model that determined habitat utilization based on habitat availability using a geographic information system (GIS) database. Observed foraging activities and those predicted from feathers both suggested that some adult storks preferred to feed their young freshwater prey, even when saltwater resources were more accessible in the local environment. This conclusion supports the contention that wood stork populations are sensitive to changes in the distribution of freshwater habitats along the southeastern coastal plain of the United States.
从佐治亚州的两个内陆繁殖地和两个沿海繁殖地收集了雏木鹳（美洲木鹳）的绒羽和反刍物。分析了这些物质中碳（C/C）和氮（N/N）的稳定同位素比率，以深入了解幼鹳的出生地以及成年鹳的觅食活动。内陆和沿海繁殖地的绒羽在δC上存在差异，其平均同位素值反映了食物网底部生物量中固定碳的来源。内陆繁殖地的羽毛在δN上因繁殖地而异，而沿海繁殖地的羽毛则没有。这些模式主要反映了亲代鹳的觅食活动，每个繁殖地的个体捕获不同营养级别的猎物的比例不同。总体而言，羽毛角蛋白的碳和氮同位素特征被用于区分每个繁殖地的雏鸟，但来自不同繁殖地的鹳在共同湿地觅食的情况除外。反刍物中食物项目的稳定同位素组成被用于重建木鹳觅食的生态系统的营养结构。基于角蛋白同位素组成预测的觅食活动通常与反刍物中观察到的猎物类型百分比（淡水与咸水以及低营养级与高营养级消费者）一致，但圣西蒙斯岛的沿海繁殖地除外，那里羽毛的δC强烈表明淡水猎物是饮食的重要组成部分。通过使用固定翼飞机对成年鹳觅食行程进行空中跟踪，解决了这种不一致性。观察到的觅食活动支持了基于羽毛稳定同位素含量的解释，表明后者比单独的反刍物分析能更好地记录总体觅食活动。将观察到的觅食模式与一个统计模型的预测结果进行了比较，该模型使用地理信息系统（GIS）数据库根据栖息地可用性确定栖息地利用情况。观察到的觅食活动以及从羽毛预测的觅食活动都表明，一些成年鹳即使当地环境中更容易获得咸水资源，也更喜欢给幼鸟喂食淡水猎物。这一结论支持了木鹳种群对美国东南沿海平原淡水栖息地分布变化敏感的观点。
