Predation risk in tree squirrels: implications of the presence of free-ranging dogs

Abstract

Small mammals show variations in activity patterns due to the use of resources and the risk of predation. However, in the case of tree squirrel species, the factors that affect their activity patterns are poorly studied. We used camera trapping to investigate the activity patterns of three different squirrel species of the genus Sciurus, two species of squirrel (Sciurus aureogaster and S. oculatus) from Mexico and one from the Iberian Peninsula (S. vulgaris). In addition, we compared their activity patterns with the potential predator community and their most important predators (Mexico: gray fox Urocyon cinereoargenteus, ringtail Bassariscus astutus, Opossum Didelphis virginiana; Spain: red fox Vulpes vulpes, pine and stone marten Martes spp.), and with feral and free-ranging dogs (Canis lupus familiaris). We evaluated the predation risk by the carnivore community on the squirrels when they descend to the ground by studying their temporal overlap and observing if the squirrels have different activity patterns adjusted to the carnivore community in each study area. The results showed that the three species of squirrels consistently descended to the ground during the day, showing a variable maximum peak of activity between 8:00 and 12:00 h. Temporal overlap of activity patterns of the three species with the carnivore community was low (Δ = 0.12–0.36), same as with the main predators (Mexico: gray fox Δ = 0.14–0.21, ringtail Δ = 0.08–0.09, opossum Δ = 0.06–0.07; Spain: red fox Δ = 0.39, martens Δ = 0.22). However, temporal overlap of activity patterns with the domestic dog was moderate-high in the three squirrel species (Mexico Δ = 0.55–0.88, Spain Δ = 0.79). These results show that the species of the genus Sciurus have adjusted their activity patterns of ground use to reduce predation risk by wild predators but not with feral and free-ranging dogs, something which can pose a serious conservation problem for these species.