Shifts in the trophic ecology of feral cats in the alpine ecosystem of an oceanic island: implications for the conservation of native biodiversity

Cats, introduced on thousands of islands worldwide, are one of the greatest threats to native wildlife. An analysis of 301 scats was performed in order to study the diet of cats in a National Park in the alpine ecosystem of an oceanic island (Tenerife, Canary Islands). The results were compared with those obtained 35 years ago. In this study, eight types of vertebrates were detected in the cat diet: two endemic reptiles, four introduced mammals, and two birds. Although introduced rabbits were the most important prey, accounting for 53.9% of the biomass in the diet, this figure is among the lowest recorded in the Canary Islands. Data show a shift from the diet 35 years ago, with a decrease in the percentage of rabbits consumed, from 73% of diet biomass in 1986 to 53.9% today, and an increase mainly not only in reptiles but also in native birds. This change is due to a decrease in the rabbit population, probably motivated by the incidence of haemorrhagic disease (RHDV2). Using a daily intake of 170 g, we estimated that a single cat could prey on 1331 vertebrates/year. Assuming a low cat density of 1 cat/km², the total cat population in the National Park would kill 257,739 vertebrates, being native species particularly vulnerable to predation, with 166,249 reptiles and 5588 birds annually. Thus, with the aim of updating and improving management strategies for the conservation of native biodiversity, there is a need for new research on invasive predators on islands where diet may change over time.