Abstract
Introduced predator mammals have caused significant impact on New Zealand’s native species, typical of the global phenomenon of biodiversity loss caused by biological invasions. Introduced predators need to find the required resources across a hierarchy of spatial and temporal scales to survive in recipient ecosystems. Improved understanding of the ecological and behavioural processes mediating resource selection can be used to improve strategies to control introduced mammal populations using traps and poison baits. Areas of high-use by predators can be related to specific microhabitat characteristics, and ultimately the distribution and availability of suitable microhabitats patches within selected macrohabitats will determine home range establishment and thus species distribution. Hence, identifying and quantifying the landscape configuration and composition of high-use areas of target species at fine-scale can inform trap or bait station placement so as to maximise likelihood of encounter within managed areas.
Spatial ecology research is being facilitated by current technical advances in remote sensing, spatial analysis tools and methods, and wildlife tracking systems. This project applies Global Positioning System (GPS) tracking and remote sensing techniques to quantify fine-scale resource selection by two introduced predators, the feral cat (Felis catus), the largest introduced carnivore in New Zealand, and the European hedgehogs (Erinaceus europaeus) one of the smaller predators. Both species represent different behavioural patterns, require different designs of lightweight GPS-devices, and pose a threat to ground nesting birds, such as the critically endangered black-stilt (Himantopus novaezelandiae) in braided rivers of the central South Island. Technical advances now make it possible to track medium-to-small mammals using GPS devices. However, limitations of the new technology have been assessed only for applications on large mammals and thus an evaluation for smaller species, with different behaviours and use of microhabitat features, is required. This research demonstrates through stationary, movement and on-animal tests, that lightweight GPS-collars perform on average similarly to the larger and heavier collars deployed on larger mammals.
Models of animal movement and resource selection at fine-scale require the collation of landscape covariates with higher spatial details than those available from most resource maps currently in use. The combination of very high spatial resolution (VHSR) satellite imagery, including spectral-rich multispectral bands and spatial rich panchromatic band, and classification techniques on object-based imagery analysis (OBIA) was used to derive resource maps from which were extracted landscape cover and metrics at fine-scale. The classification of a Quickbird image covering the selected study area (Godley Valley) using OBIA reveals that heterogeneous patchy landscapes can be more accurately classified and small features (e.g., shrub clumbs) better identified by using these techniques. The level of accuracy required depends on the ecological question and whether this question can justify the extra cost of incorporating the panchromatic band.
Analyses on the spatial ecology of feral cats revealed that the species mainly establish home ranges conditioned by rabbit (Oryctolagus cuniculus) abundance, including mosaics of pastures and shrubs at low elevation, and other variables such as presence of boulders on scree slopes for den sites. Core areas of high use are mainly composed of pasture and shrub mosaics.
Hedgehogs establish home ranges in landscape mosaics most likely supporting high invertebrate abundance (i.e., high productivity vegetation such as green pastures), habitat edges for dispersal movement, near tracks and avoiding proximity to gravel roads. Core areas of high use are mainly mosaics of green pastures, tussocks (to provide food and dry nesting materials) and shrubs (shelter).
Traps and poison bait stations used for lethal control of these two introduced mammalian pest species are recommended to be placed according to the specific landscape patterns identified as important for each respective species.
The satellite-based techniques presented in this thesis have been shown to provide data suitable for analysis using current methods to study the resource selection of medium-to-small mammals. Applications of this technology could be extended to address more mechanistic approaches to studies of individual activity patterns, movement behaviour, and intraspecific interactions.