Aspects of mammalian predator ecology co-inhabiting giant skink habitat

Abstract

The utilisation of habitats and the diet of feral cats and ferrets was studied in an area co-inhabited by giant skinks in the Middlemarch-Macraes Flat region of Central Otago, New Zealand. Home range and habitat utilisation of two female cats, two male cats and three male ferrets using radio telemetry revealed that; female feral cat home range varied from 0.52 krrr to 1.45 km2; male feral cat range varied from 1.80 km.2.to 2.00 km.2, and male ferrets from 0.68 km:zto 1.20 km.2: Predators made non-random use of certain parts of their home range and this was related to food acquisition and the position of predator dens. Digestive tracts and scats indicated that rabbits, birds, and insects were the staple food of both feral cats and ferrets in pasture, semi-arid, and tussock habitats. In addition, prey remains in feral cat scats indicated that common skinks were an important food item of feral cats. Dead farm stock were an important source of food during winter for individuals of both the feral cat and ferret populations. Topography and sub-habitats affected the distribution of prey, and therefore influenced the areas of high utilisation of predators. Pathways used by predators to travel through an area were mainly stock tracks and fence lines. Interfaces between tussock and pasture habitats were used as pathways for feral cats, while ferrets made use of tussock gullies. This study shows that habitat utilisation by feral cats within fragmented tussock grassland and pastures has the potential to reduce local populations of lizards. Ferrets pose a negligible threat to lizards in the present study area. An easily scavengable food supply, e.g. stock carcasses, available to predators during winter is important for maintaining feral cats and ferret populations and therefore such a supply has important consequences for lizard conservation. Lizard conservation will be aided primarily by habitat improvement.