Evidence of Seabird Consumption by Introduced House Mice on isla La Vieja, Peru Signals Potential Risk to Peruvian Diving-Petrels Pelecanoides garnotii

Introduced rodents are among the leading threats to island biota. On La Vieja Island, Peru, house mice Mus musculus have been present for decades and may have affected native seabirds. We assessed mouse diet to evaluate potential impacts on the Peruvian diving-petrel Pelecanoides garnotii nesting on La Vieja Island. Stomach contents from 234 mice captured across seven field seasons between 2020 and 2024 were examined. Feathers were the most frequent item observed (62% by frequency of occurrence), followed by mammalian fur (44%), unknown arthropod remains (28%), ticks (15%), and arthropod larvae (14%). Feather morphology and coloration were consistent with P. garnotii, but species-level assignment was not possible, and the origin of avian material (scavenging vs. predation) remains uncertain. Nonetheless, the high prevalence of feathers in mouse diets within diving-petrel nesting habitat indicates a credible risk to this vulnerable, burrow-nesting seabird. Diet composition did not differ significantly between mouse sexes or among five island sectors. These results provide the first quantitative description of M. musculus trophic ecology on La Vieja Island and establish a baseline for management. Given global evidence of mouse impacts on Procellariiforms, our findings support a precautionary approach: targeted research (e.g., DNA metabarcoding of feathers/feces, burrow cameras) combined with proactive rodent control or eradication planning and strengthened biosecurity to mitigate potential impacts on Peruvian diving-petrels.