Methodological improvements for detecting and identifying scats of an expanding mesocarnivore in south-western Europe

The use of scats is a widespread non-invasive method in ecological studies of mammalian carnivores. However, their low detectability and the incorrect species assignment may be important sources of bias. We aimed to optimize the detection and identification of scats of Egyptian mongoose (Herpestes ichneumon), using the red fox (Vulpes vulpes) as a comparative model. Based on molecular identification of scats we assessed: (1) the accuracy of species morphological identification (Field-ID); (2) whether post-field laboratory analyses (FL-ID) improve Field-ID; (3) species-specific morphological differences of scats, and (4) whether specific field surveys increase the detectability of mongoose scats. Out of 175 collected scats, 81 were genetically identified. Field-ID accuracy was over 75.6% for the mongoose and over 45.0% for the red fox. Misidentified mongoose scats mainly belonged to stone marten (50.0%) while misidentified red fox scats mainly belonged to mongoose (63.6%). After applying FL-ID, accuracy increased to 93.1% for the Egyptian mongoose and 76.2% for the red fox. Morphological scat differences were only significant for the scat diameter, with red fox scats being significantly thicker than those of mongoose. More mongoose scats were found along ecotones (mean ± SE: 4.05 ± 1.45 scats/transect) than along trails and roads (0.05 ± 0.05 scats/transect), while red fox scats were found similarly in both transect types. The application of post-field analysis to scats and focusing the search along ecotones optimized both the identification accuracy and the detection probability of Egyptian mongoose scats, although searching for scats in other structures should not be discarded if the aim is the study of habitat use or selection by the species. Our results can be useful for scat identification in studies on this and other carnivore species.