Long-distance migratory birds rely on pre-migratory fuelling to complete extensive flights. Global change and invasive species may threaten food resources critical for this process. The Bristle-thighed Curlew Numenius tahitiensis breeds in Alaska and winters across Pacific islands. Its population in French Polynesia has halved in the past two decades, raising conservation concerns. Introduced Pacific rats Rattus exulans are suspected to deplete terrestrial food resources on atolls, potentially impacting curlew fuelling. This study characterises the diet of Bristle-thighed Curlews during April, their pre-migratory fuelling period, using DNA metabarcoding of 61 faeces collected across rat-infested and rat-free islands in the Tuamotu Archipelago – of which 38 provided dietary data. Several molecular operational taxonomic units (MOTUs) were identified, covering arthropods, annelids, nemerteans, molluscs, reptiles, and plants. The curlew’s diet was dominated by crabs (45.8% MOTUs, 66.1% reads), particularly Pachygrapsus fakaravensis and Grapsus albolineatus, followed by insects (35.8% MOTUs, 11.5% reads), notably Pycnoscelus cockroaches. Plant material, mainly from coconut trees, represented 17.4% of reads. The diet was significantly more diverse on rat-infested islands, with higher MOTU richness and a predominance of crabs (73.7% reads). In contrast, rat-free islands showed a more balanced intake among crabs, insects, and plants. Rat presence shifts dietary diversity and composition, possibly by altering prey availability. Despite greater diversity on rat-infested islands, optimal fuelling appears to be associated with abundant crabs and insects on rat-free islands. Findings highlight the importance of managing invasive rats to maintain key food resources for this Endangered migratory bird. Further research on prey availability and nutritional quality across islands is recommended to inform conservation strategies.