A total of 146 scats were collected on eight areas that were surveyed weekly (from September 2010 to August 2011). Within each area, a survey consisted of a 1-km transect around pastures that are heavily used by cats on Corvo (Hervías et al., 2012; Oppel PKC412 supplier et al., 2012): near seabird colonies, near haylofts with suitable shelter and near rock walls (Fig. 1). Individual prey items were identified using reference material from our own collection. Dietary information is presented in terms
of number of prey, percentage of prey items (%RF), frequency of occurrence (%F) and biomass (%B; Supporting Information Table S1). From these measures we calculated an index of relative importance (IRI) as %F * (%RF + %B) to rank prey according ZD1839 cell line to its relative importance, in order to reduce possible bias in dietary description due to species size (Medina et al., 2010). Human and vegetable food was excluded. We measured the relative abundance of four prominent prey taxa (rodents, landbirds, seabirds, invertebrates) in the main habitat type on the island
(pastures) where all cat scat transects were located (Fig. 1). For rodents we surveyed areas at two different altitudes: two grids <250 m and two grids >250 m. Because the abundance of invertebrate species can vary with the intensity of pasture management (Cardoso et al., 2009), we surveyed invertebrates within an area with a gradient from grazed to un-grazed grassland. For landbirds 10 randomly-selected locations were surveyed across the island. The abundance of rodents was estimated using live-traps. Rodents were trapped for four consecutive nights every month from March 2010 to February 2011, except in July and December Methocarbamol 2010. Traps were wired open and left un-baited between seasons to reduce trap-shyness (Hervías et al., 2012). We calculated an abundance index per season as the number of individuals captured
per 100 trap nights for each rodent species. For landbirds, five-minute point counts were conducted in September and December 2010 and March and June 2011 by the same observer during favourable weather within four hours after sunrise. Because the landbird community on Corvo is species-poor (seven species), we used the total number of all species, seen or heard, during a survey as an index of landbird abundance. Landbirds are more conspicuous during their breeding season and this behaviour increases both the likelihood of detection and predation by cats (Brown et al., 1998). To reduce confounding abundance with increasing detectability due to singing behaviour, we counted only birds that were detected by their contact or alarm calls in each season. Among seabirds, we focused on Cory’s shearwater Calonectris diomedea borealis because it is the most common species on Corvo, and probably the only seabird species accessible for cats.