Improving morphological diet studies with molecular ecology: An application for invasive mammal predation on island birds

On islands, invasive predators, particularly feral cats and rats, are key drivers of bird population decline and extinction. Diet studies can be used to assess predator impacts on prey populations. Here we first evaluated the resolution of morphological identification (Class to Species) of bird remains in cat and rat diet studies. We also analysed the effect of predator size/type (cat vs rat) and sample type (faecal vs stomach contents) on the taxonomic level of bird identification. We found that difficulty in identifying bird remains significantly increased with taxonomic resolution (from Class to Species) for both predators. Bird identification was more accurate in cat than in rat diets and no sample-type effect was detected in cat diets. Second, we developed a set of molecular resources (DNA sequence database and bird-specific primer pairs) to detect and identify bird DNA. We tested and validated primer pairs' taxonomic coverage and specificity using in silico and in vitro analyses. The performances of morphological and molecular methods were then compared in a case study of cat and rat diet samples collected on Niau Atoll (French Polynesia). Our results highlight the efficiency of the molecular method in both detection and high-resolution identification of birds in predator diet samples. As robust qualitative and quantitative diet analyses are required to accurately assess predator impacts on prey populations, we recommend combining morphological and molecular methods to maximise bird detection, identification and quantification, especially when rare or threatened birds are at stake. (C) 2015 Elsevier Ltd. All rights reserved.