Distribution and diet of feral cats (Felis catus) in the Wet Tropics of north-eastern Australia, with a focus on the upland rainforest

Abstract

ContextFeral cats have been identified as a key threat to Australia’s biodiversity, particularly in arid areas and tropical woodlands. Their presence, abundance and potential impacts in rainforest have received less attention. AimsTo investigate the distribution and diet of feral cats (Felis catus) in upland rainforest of the Wet Tropics. MethodsWe collated available occurrence records from the Wet Tropics, and data from upland camera-trapping surveys over an 8-year period, to assess geographic and elevational distribution of feral cats in the bioregion. We also assessed the diet of feral cats from scats collected at upland sites. Key resultsFeral cats are widespread through the Wet Tropics bioregion, from the lowlands to the peaks of the highest mountains (>1600m), and in all vegetation types. Abundance appears to vary greatly across the region. Cats were readily detected during camera-trap surveys in some upland rainforest areas (particularly in the southern Atherton Tablelands and Bellenden Ker Range), but were never recorded in some areas (Thornton Peak, the upland rainforest of Windsor Tableland and Danbulla National Park) despite numerous repeated camera-trap surveys over the past 8 years at some of these sites. Scat analysis suggested that small mammals comprise ~70% of the diet of feral cats at an upland rainforest site. Multivariate analysis could not detect a difference in mammal community at sites where cats were detected or not. ConclusionsFeral cats are widespread in the Wet Tropics and appear to be common in some upland areas. However, their presence and abundance are variable across the region, and the drivers of this variability are not resolved. Small mammals appear to be the primary prey in the rainforest, although the impacts of cats on the endemic and threatened fauna of the Wet Tropics is unknown. ImplicationsGiven their documented impact in some ecosystems, research is required to examine the potential impact of cats on Wet Tropics fauna, particularly the many upland endemic vertebrates. Studies are needed on (1) habitat and prey selection, (2) population dynamics, and (3) landscape source–sink dynamics of feral cats in the Wet Tropics.

Camera‐trapping density estimates suggest critically low population sizes for the Wet Tropics subspecies of the spotted‐tailed quoll (Dasyurus maculatus gracilis)

“…Direct control of invasive species, such as hand‐removing R. marina along roads at Windsor Tableland, Carbine Tableland and Lamb Range (Uzqueda et al, 2020) will likely benefit the subspecies. The Bellenden Ker Range subpopulation is estimated herein to be small and is known to co‐occur with an apparently high density of F. catus (Rowland et al, 2020b). These may be a direct threat to D. m. gracilis through competition and potential disease transfer (Burnett & Marsh, 2004).…”

“…relatively high prey diversity and/or density). The subspecies primarily feeds on small to medium‐sized mammals (Burnett, 2001), which are higher in diversity and abundance in the uplands of the Wet Tropics (Rowland et al, 2020b; Williams, 1997; Williams et al, 2010). Upland restriction may also be determined by the distribution of identified threats, which are generally associated with human activities and hence decrease with rainforest patch size and distance to the edge (Burnett & Marsh, 2004; Uzqueda et al, 2020).…”

Laying low: Rugged lowland rainforest preferred by feral cats in the Australian Wet Tropics

“…National parks generally had higher relative abundance estimates than non-national park areas (Figure 2). There were 524 independent detections of feral cats throughout the duration of the surveys, resulting in a trapping rate of 5.09 photographs/100 days, approximately 11 times higher than the only other estimate for the region of 0.45 photographs/100 days (recalculated from Table 1 [ Rowland et al, 2020]). Feral cats were detected at least once at 63/90 sites included in the occupancy analysis.…”

“…Williams, unpublished data), which provides ample prey for feral cats regardless of elevation. As small mammals constitute 70% of the diet of feral cats in the region (Rowland et al, 2020) and feral cat population densities and their degree of home-range overlap are primarily driven by prey abundance (Edwards et al, 2001), one would expect relative abundance to be uniform across the elevation gradient and thus occupancy to remain similar if prey availability were responsible for this pattern. Consequently, the accelerated decline of occupancy for feral cats after mid-elevation is more likely due to other factors, such as increasingly harsh environmental conditions in terms of rainfall and temperature.…”

Cat ecology, impacts and management in Australia

“…For example, estimates of cat density or activity have been rare from some habitats including tropical rainforests and topographically rugged landscapes. Papers by Lavery et al (2020) for the Solomon Islands and Rowland et al (2020) in Queensland describe the density or occurrence of cats in rainforests, and McDonald et al (2020) document cat density in rugged environments of central Australia. Hohnen et al (2020a) and Miritis et al (2020) estimate cat densities for Kangaroo Island and French Island respectively.…”