Diet of feral cats during the Scopoli’s shearwater breeding season on Linosa Island, Mediterranean Sea

Abstract

Feral cats (Felis catus) are considered to be one of main successful invasive species of island ecosystems. The introduced cats often negatively affect seabird populations due to the lack of anti-predatory strategies resulting from the absence of mammalian terrestrial predators during their evolutionary development. Linosa Island hosts the second largest colony of Scopoli’s shearwater (Calonectris diomedea) of the species. In this study, we estimated the number of cats on Linosa Island and we evaluated their diet using a non-invasive method: scat analysis. Scat collection took place in the northern part of the island in the Scopoli’s shearwater colony, where a feral cat colony lives permanently. We analysed a total of 188 cat scats, collected during the different stages of the shearwater breeding period. Introduced mammals were the most frequent preys: wild rabbits and black rats occurred in scats with the same frequency (28.72%). Birds were the second most frequent prey category found, primarily represented by the seabird Scopoli’s shearwater (16.49%). The cats’ diet varied seasonally in relation to prey availability and accessibility: shearwaters were mainly preyed upon during spring when they exhibited the greatest vocal activity and spent the most time out of their nests. Regarding the biomass, mammals were the dominant prey, and wild rabbits were the most consumed species. However, Scopoli’s shearwater represented approximately one-third of the total biomass consumed. Consequently, the management of feral cats living in proximity of the seabird colony is strongly required, and the increase of “trap-neuter-release” (TNR) programmes is necessary in order to avoid uncontrolled gains in the cat population on Linosa Island. Since the cats have a crucial role in controlling the rat population (the main threat for shearwaters), before planning management strategies, the complex inter-relationship that exists between species must be taken into account.