Northern Macronectes halli and southern giant petrels M. giganteus are opportunistic predators and the dominant avian scavengers in sub-Antarctic and Antarctic ecosystems. At South Georgia, there are globally important breeding populations of both species; however, no detailed diet study has been carried out at this site for > 35 years. Here, we analysed stomach contents of northern (n = 81) and southern giant petrel (n = 73) chicks at Bird Island, South Georgia (2014/15–2016/17). Specifically, we investigated: (1) interspecific and sexual dietary segregation; (2) diet changes within and among recent years; and (3) long-term diet changes since 1979/80–1980/81. Overall diet composition was similar between species, with penguins comprising approximately half the diet by mass. In both species (but more pronounced in southern giant petrels), prey delivered by female parents included higher proportions (by mass) of penguins and Antarctic krill Euphausia superba, and by male parents included more Antarctic fur seal Arctocephalus gazella carrion and seabirds other than penguins. Consumption of penguins increased, and of seal carrion declined, as chick-rearing progressed, mirroring the decreasing availability of the latter after the peak pupping period in December at South Georgia. Comparisons with data from 1979/80–1980/81 suggest some changes in giant petrel diets; however, these differences were no greater than the typical annual variation, and there were no clear links between diet and breeding allochrony or the differing population trends (more rapid increase in northern than southern giant petrels). The high diet diversity and ability of giant petrels to exploit both carrion and marine prey facilitates coexistence with other sympatric Procellariiformes and explains their favourable population status.

北部的Macronectes halli和南部的巨大海燕M. giganteus是南极和南极生态系统中的机会性掠食者和占主导地位的清道夫。在南乔治亚州，这两个物种在全球都具有重要的繁殖种群。然而，在这个地方，没有进行详细的饮食研究超过35年。在这里，我们分析了北方（n  = 81）和南方巨海燕（n = 73）南乔治亚州伯德岛的小鸡（2014 / 15–2016 / 17）。具体而言，我们调查了：（1）种间和性饮食隔离；（2）近年来及其之间的饮食变化；（3）自1979 / 80-1980 / 81年以来的长期饮食变化。物种之间的总体饮食组成是相似的，其中企鹅约占饮食的一半。在这两个物种中（但在南部大海燕中更为明显），雌性父母递送的猎物包括较高比例（按质量计）的企鹅和南极磷虾Euphausia superba，雄性父母递送的猎物包括更多的南极海狗Arctocephalus gazella除企鹅以外的腐肉和海鸟。随着小鸡饲养的发展，企鹅的消费增加了，海豹腐肉的消费减少了，这反映了在12月南佐治亚州的成年幼犬高峰期后，企鹅的供应量正在减少。与1979 / 80-1980 / 81年的数据进行比较，结果表明巨海燕的饮食有所变化。然而，这些差异不大于典型的年度差异，并且饮食与繁殖异时之间或不同的种群趋势之间没有明确的联系（北部比南部巨型海燕增长更快）。高度的饮食多样性和巨型海燕利用腐肉和海洋猎物的能力促进了与其他同胞Procellariiformes的共存，并解释了它们的有利种群地位。