DOI: 10.5061/dryad.2v6wwpzq4
title: Laying low: Rugged lowland rainforest preferred by feral cats in the Australian wet tropics

description: Invasive mesopredators are responsible for the decline of many species of
 native mammals worldwide. Feral cats have been causally linked to multiple
 extinctions of Australian mammals since European colonisation. While feral
 cats are found throughout Australia, most research has been undertaken in
 arid habitats, thus there is a limited understanding of feral cat
 distribution, abundance, and ecology in Australian tropical rainforests.
 We carried out camera-trapping surveys at 108 locations across seven study
 sites, spanning 200 km in the Australian Wet Tropics. 
 Single-species occupancy analysis was implemented to investigate how
 environmental factors influence feral cat distribution. Feral cats were
 detected at a rate of 5.09 photographs/100 days, 11 times higher than
 previously recorded in the Australian Wet Tropics. The main environmental
 factors influencing feral cat occupancy were a positive association with
 terrain ruggedness, a negative association with elevation, and a higher
 affinity for rainforest than eucalypt forest. These findings were
 consistent with other studies on feral cat ecology but differed from
 similar surveys in Australia. Increasingly harsh and consistently wet
 weather conditions at higher elevations, and improved shelter in
 topographically complex habitats may drive cat preference for lowland
 rainforest. Feral cats were positively associated with roads, supporting
 the theory that roads facilitate access and colonisation of feral cats
 within more remote parts of the rainforest. Higher elevation rainforests
 with no roads could act as refugia for native prey species within the
 critical weight range. Regular monitoring of existing roads should be
 implemented to monitor feral cats, and new linear infrastructure should be
 limited to prevent encroachment into these areas. This is pertinent as
 climate change modelling suggests that habitats at higher elevations will
 become similar to lower elevations, potentially making the environment
 more suitable for feral cat populations.
description: General camera
 deployment 108 Camera-trap pairs were placed along main
 roads, four-wheel-drive tracks, and walking trails with one camera-trap
 facing into the road and another camera-trap positioned in
 the habitat, 50 m perpendicular from the road. To test the hypothesis
 feral cats would be more likely to use roads in tropical forests we placed
 a camera in the forest. A length of 50m was used to counteract potential
 spatial avoidance by feral cats of habitat features favoured by dingoes
 (Canis lupus dingo), the apex predator in Australia (Fancourt et al., 2019). We treated
 both cameras, on-road and off-road, as a single site for analyses due to
 their proximity to one another. Each camera-trap pair's planned
 location was spaced 2.2 km along the road; this distance exceeded the
 predicted home range of 1.16 km for feral cats in productive, low
 seasonality environments like rainforests and matched the home-range
 estimate of female feral cats in a montane rainforest in Hawaii (Bengsen et al., 2016; Smucker et al.,
 2000).
 Nineteen opportunistic camera-trap pairs were placed on
 walking trails and old roads that were not present on maps of the study
 areas. These opportunistic deployments were placed 500 m-1.98 km from the
 nearest camera-trap pair using the road. This deployment strategy resulted in an average
 distance of 1.81 km between camera-trap sites based on the distance to the
 nearest neighbouring camera-trap site using the road network. Due to
 uncertainty around cat home ranges in the study area, there is a potential
 for individual feral cats to be detected at multiple cameras. To be
 conservative, we interpret the occupancy results as the probability of
 site use rather than true occupancy, which is the same approach as other
 studies on feral cats in Australia and carnivore surveys generally
 (Doherty et al., 2021; MacKenzie et al., 2017; Rogan et al., 2019).
 Surveys were conducted between April 2019 and July 2020 for a minimum of
 six weeks per survey.
 We did not use baits or
 lures in front of the camera-traps as their use can influence species
 behaviour in an unknown way if it has not been evaluated previously,
 causing either a repellent, attractive, or neutral response (Mills et al.,
 2019; Rocha et al., 2016). Camera placement and settings.
 We followed the general guidelines for
 camera-trap deployment recommended by Meek et al. (2012). At each
 camera-trap site, a Bushnell Trophy Aggressor No-glow camera (Bushnell
 Outdoor Products, Kansas, USA) was placed facing the road within 200m of
 the planned point. Camera-traps were placed facing the road, perpendicular
 to the direction animals would travel, to maximise the likelihood of
 detecting our target species (Wang et al., 2019).
 Camera-traps were positioned at a height of 20-45cm from the ground, as
 this is the approximate height of the centre of mass for an adult feral
 cat (McGregor et al., 2015). Cameras were angled to be parallel with the
 terrain they were facing. Cameras were not orientated at a specific
 compass bearing as we were following the road to place cameras and
 prioritised angling the camera perpendicular to the animal's expected
 travel route. For each road camera location, a single No-glow Bushnell
 Natureview (Bushnell Outdoor Products, Kansas, USA) was placed 50 m from
 the road in the forest with a consistent
 and unobstructed field of view. Vegetation and debris were
 removed to a minimum distance of 4 m in front of the camera-trap where
 necessary to ensure a clear field of vision over the survey period. All
 camera-traps were programmed to take three images per trigger, with no
 delay between triggers (recovery time between consecutive photos = 0.62 s
 for Bushnell Aggressor, 0.7 s Bushnell Natureview). Due to equipment
 failure, four of the forest camera-traps at Mount Zero-Taravale Wildlife
 Sanctuary were replaced with Reconyx Hyperfire PC800 infrared cameras.
 While different camera-trap brands have different detection probabilities,
 the fact that feral cats were rarely detected off roads in our study makes
 it unlikely this difference affected our results (Palencia et al., 2022). The
 infrared flashes on the road camera-traps were set to high to ensure as
 much of the road as possible would be visible in the pictures, whilst
 forest infrared flashes were set to low to avoid overexposing the image.
 The remaining settings were all left at their factory defaults.
 Predictor variables of feral cat
 occupancy To investigate spatial factors that influence
 feral cat occupancy, we collated environmental and anthropogenic variables
 that are hypothesised to alter feral cat distribution and site use
 (Doherty et al., 2015a). We tested hypotheses related to
 terrain (elevation, terrain ruggedness index), habitat (habitat type,
 understory vegetation density), anthropogenic disturbance (distance from
 the nearest human population, forest integrity, habitat fragmentation),
 primary productivity (mean annual rainfall), prey populations (biomass
 index of prey species), invasive herbivores (invasive herbivore trapping
 rate), and altered fire regimes (fire regime intensity). For a complete
 list of the variables considered, how they were calculated, and the
 hypothesis they are linked to see Table S1. As there is little known about
 the spatial scale at which predictor variables affect feral cat occupancy,
 each model covariate value was averaged over a 2.2 km2 circular area
 around the camera point (Stobo-Wilson
 et al., 2020). The
 averaging of a spatial covariate was done to capture the variable at a
 scale relevant to the home range of a feral cat in rainforest habitats.
 This is pertinent as the effective area surveyed by the camera trap is
 only relative to the sensor's detection zone, not the wider area we
 averaged for the environmental covariates (MacKenzie et al.,
 2017). All continuous variables were checked for correlation
 before analyses. If any variable pairing resulted in a Spearman
 correlation coefficient &gt;0.7, we only retained what we considered
 to be the most biologically relevant variable. The remaining variables
 were then scaled to improve model performance. To consider survey biases,
 we used observation level covariates in the analysis. We used the survey
 effort (the total number of days both cameras were actively trapping at
 each site for each occasion) to account for variable camera performance of
 both the road and off-road cameras at each camera-trap site influencing
 detection probability. 
description: The data provided are as follows; 1.
 Feral_cat_Pres_abs_DRYAD_FINAL.csv - A presence-absence matrix of feral
 cat detections. 1 means detected, 0 not-detected, NA the camera site was
 not active for most of the occasion (&lt;3 days). 
 2.Site_Covs_DRYAD.csv -  The site covariates needed to run the
 analysis. All need to be scaled to be run in the analysis. 
 3.Obs_Covs_DRYAD.csv - Survey level co-variates, scaled
 camera-trap effort per site per occasion.  Software
 needed is R and the packages required are in the Rmarkdown
 file.