Estuarine crocodiles in a tropical coastal floodplain obtain nutrition from terrestrial prey

The estuarine crocodile (Crocodylus porosus) is one of the largest and most widespread crocodilians in the world. Although considered an apex species, the role of the estuarine crocodile in aquatic foodwebs is poorly understood; we know what crocodiles ingest, but not what nourishes them. In this study, we used a combination of stable isotope measurements (δ13C, δ15N, and δ34S) and direct feeding observations to identify the source of nutrition of estuarine crocodiles in Kakadu National Park, Northern Australia. Our results show that most crocodiles sampled (size 850 – 4200mm, with 76% of them being > 2.5 m) consume a large variety of prey, however a large proportion of their nutrition is derived from terrestrial prey. Introduced species such as water buffaloes (Bubalus bubalis) and pigs (Sus scrofa) could contribute between 53 and 84% to the nutrition of the sampled crocodiles. The isotopic composition of large crocodiles (total length > 3 m) suggested possible increase in marine prey consumption with size (R2 = 0.30; p = 0.005). Additionally, we found crocodiles sampled in the dry season had on average higher terrestrial contributions compared to crocodiles sampled during the wet season (84.1 ± 2.4% versus 55.4 ± 7.0%). Overall, we found that terrestrial prey are important source of nutrition for many crocodiles in this region where introduced herbivorous mammals are abundant.

湾鳄（Crocodylus porosus）是全球体型最大、分布最广的鳄类之一。尽管被视为顶级捕食者，但其在水生食物网中的生态功能仍未得到充分阐明；我们仅知晓湾鳄的摄食对象，却难以明确其真正的营养来源。本研究结合稳定同位素检测（stable isotope measurements）与直接摄食观测数据，对澳大利亚北部卡卡杜国家公园内湾鳄的营养来源进行了分析。本次采样的鳄类体长范围为850~4200mm，其中76%的个体体长超过2.5米；结果显示，多数采样鳄类的摄食猎物种类多样，但它们的大部分营养却来自陆生猎物。外来物种如亚洲水牛（Bubalus bubalis）与野猪（Sus scrofa）可贡献采样鳄类53%~84%的营养供给。体长超过3米的大型鳄类的同位素组成表明，其海洋猎物的摄食比例可能随体型增大而上升（R²=0.30；p=0.005）。此外，本研究发现旱季采样的鳄类，其营养来源中陆生猎物的占比平均高于雨季采样个体（分别为84.1±2.4%与55.4±7.0%）。综合来看，在该外来植食性哺乳动物种群丰富的区域内，陆生猎物是多数湾鳄的重要营养来源。