Diet study of free-ranging cats from Madeira Island

Oceanic islands harbour some of the planet's most unique ecosystems and are particularly vulnerable to the impact of introduced predators. Of these, free-ranging cats (Felis catus) are particularly detrimental and have been linked to the extinction and population decline of numerous insular taxa. Yet, a more holistic understanding of the impacts of free-ranging cats on oceanic islands has been hampered by an incomplete understanding of their diet and population densities. Using a peri-urban protected area in the subtropical Madeira Island as a case-study, we combined DNA metabarcoding, morphological scat analyses and camera trapping to investigate the magnitude of native and introduced prey consumption by invasive felines. Samples were collected from a total of 58 cat scats in the summer and autumn of 2021. Overall, cats were found to prey on over 20 distinct taxa of ten orders, including native and non-native prey, as well as taxa associated with anthropogenic food. Cat diet was seasonally modulated, with a higher incidence of reptiles in summer months, relative to autumn. Although DNA metabarcoding revealed a higher diversity of prey taxa compared to traditional morphological scat analyses, both methods provided complementary insights, highlighting the benefits of their combined use. Combining diet information of both molecular and morphological analyses, with a free-ranging cat density of 1.4 cats/km2 revealed by the protected area-wise camera trap survey, we estimate an annual prey intake of over 18,000 vertebrates by cats in a protected area of 7.5 km², of which over one third correspond to native birds and reptiles. These findings underscore the complex interactions between cats and native wildlife, emphasising the need for targeted conservation strategies in ecologically sensitive areas. Further research, including year-round studies and examination of urban cat diets, is warranted to fully understand and mitigate the impacts of free-ranging cats on insular ecosystems