The current information about the diet composition of the rock shag (Phalacrocorax magellanicus) in the SW Atlantic coast comes mainly from conventional pellet or stomach content analysis from a few locations situated in northern Patagonia (Chubut Province, Argentina). In this work, we studied the diet of breeding rock shags over several years at a colony from southern Patagonia (Ría Deseado, Santa Cruz Province, Argentina) using a combined technique of conventional diet assessment (pellet analysis) and stable isotope analysis of carbon and nitrogen. Our results confirm the importance of benthic prey and the low inter-annual variability in the diet of the rock shag. These results coincide with previous research in relation to the exploitation of slow moving, predictable, but low-energy density prey. The stable isotope mixing models, which was informed with prior data obtained from pellet analysis, allowed for the detection of subtle differences between the diet of adults and chicks, consisting in the incorporation of higher proportions of cephalopods, an energy-rich prey, in the diet of chicks. By comparing our results with the diet of the red-legged cormorant, which breeds in sympatry in the Ría Deseado Estuary and whose diet composition is strongly pelagic, we suspect a certain level of trophic resource partitioning between these rock shag and red-legged cormorant.

中文翻译：

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从组合颗粒和稳定同位素分析推断的成虫和雏鸡的饮食（Phalacrocorax magellanicus）

目前关于大西洋西南部海岸岩鸬鹚（Phalacrocorax magellanicus）饮食成分的信息主要来自巴塔哥尼亚北部（阿根廷丘布特省）几个地点的常规颗粒或胃内容物分析。在这项工作中，我们使用传统饮食评估（颗粒分析）和碳和稳定同位素分析的组合技术，研究了在巴塔哥尼亚南部（阿根廷圣克鲁斯省 Ría Deseado）的一个群落中数年来繁殖岩鸬鹚的饮食。氮。我们的研究结果证实了底栖猎物的重要性和岩鸬鹚饮食的低年际变化。这些结果与先前关于开发缓慢移动、可预测但能量密度低的猎物的研究相吻合。稳定同位素混合模型，使用从颗粒分析获得的先前数据，可以检测成鸟和雏鸡饮食之间的细微差异，包括在雏鸡饮食中掺入更高比例的头足类动物，一种能量丰富的猎物。通过将我们的结果与红腿鸬鹚的饮食进行比较，红腿鸬鹚在 Ría Deseado 河口繁殖，其饮食成分具有强烈的远洋性，我们怀疑这些岩鸬鹚和红腿鸬鹚之间存在一定程度的营养资源分配。