Ferrets are labelled Unwanted Organisms under the Biosecurity Act (1993) due to their predation on New Zealand's native protected species and their status as potential vectors of Bovine Tuberculosis. There was suspicion that ferrets could detect the infrared light-emitting equipment used to monitor predator and prey behaviour. A two-alternative forced-choice operant procedure was used to test whether five pigmented male ferrets could detect infrared (870 and 920 nm) light. First, the ferrets were taught to press a lever under a lit visible (white) light emitting diode (LED) for food rewards. After up to 101 40-minute sessions, each ferret could lever press under the lit-light at or above the pass criteria of 75% responses over four consecutive (or five out of six) sessions. The same ferrets were then tested for stimulus generalisation over different stimulus properties by changing the wavelength/colour and intensity of the lit-light. The overall mean accuracy of each ferret's response to each coloured light varied between 92% and 84%. When a red light was systematically dimmed to halve the intensity nine times, all five ferrets still met the set pass criteria with overall accuracies of between 88% and 78%. This indicated that changing the properties of the light stimuli would not disrupt the ferrets' abilities to perform the learned task. This test was a necessary prerequisite before changing the light stimuli to potentially invisible wavelengths in the infrared spectrum. The light stimulus was changed to a single infrared (870) nm LED. Two of five ferrets showed strong evidence (response accuracies of 77% 4 and 72% 2) and one ferret showed weak evidence (60% 3) that they could see the light at this wavelength. Extraneous cues such as ultrasound emitted at the onset of a stimulus light or a predictable schedule of reinforcement were eliminated as potential response cues. These tests helped to prove that the ferrets were using only the light stimulus to discriminate which stimulus was lit. It may be possible that at least some feral ferrets can detect the light produced from infrared monitoring equipment that emits light wavelengths at or below 870 nm. This has significant implications for conservation because infrared equipment is used by conservation agencies in New Zealand and overseas to monitor predator and prey behaviour in the wild. If the infrared lighting is detected by the subject being observed, then it may potentially influence the behaviour of the animal, or attract a predator towards threatened native species.

This thesis is about making inference on the host status of feral ferrets in New Zealand for Mycobacterium bovis, the aetiological agent of bovine tuberculosis. The central question addressed is whether the rate of intra-specific transmission of M. bovis among ferrets is sufficient for the disease to persist in ferret populations in the absence of external, non-ferret sources of infection (inter-specific transmission). The question is tackled in three parts�firstly using model selection to identify suitable models for estimating the force of M. bovis infection in ferret populations; secondly applying statistical hypothesis testing to the results of planned manipulative field experiments to test the relationship between M. bovis infection in brushtail possums and that in ferrets; and thirdly using modelling to estimate intra-specific disease transmission rates and the basic reproductive rate (Ro) of M. bovis infection in ferrets. The model selection approach clearly identified the hypothesis of oral infection related to diet was, as modelled by a constant force of infection from the age of weaning, the best approximation of how M. bovis infection was transmitted to ferrets. No other form of transmission (e.g., during fighting, mating, or routine social interaction) was supported in comparison. The force of infection (λ) ranged from 0.14 yr-1 to 5.77 yr-1, and was significantly higher (2.2 times) in male than female ferrets. Statistical hypothesis testing revealed transmission of M. bovis to ferrets occurred from both brushtail possums and ferrets. The force of M. bovis infection in ferrets was reduced by 88% (λ=0.3 yr-1 vs. λ=2.5 yr-1) at sites with reductions in the population density of sympatric brushtail possum populations. A smaller decline in the force of infection resulting from the lethal cross-sectional sampling of the ferret populations was also demonstrated. The modelling approach estimated the basic reproductive rate (Ro) of M. bovis infection in ferrets in New Zealand to vary from 0.17 at the lowest population density (0.5 km-2) recorded to 1.6 at the highest population density (3.4 km-2) recorded. The estimates of Ro were moderately imprecise, with a coefficient of variation of 76%. Despite this imprecision, the Ro for M. bovis infection in ferrets was significantly less than unity for all North Island sites surveyed. Hence it is inferred ferrets are spillover hosts (0<Ro<1) for M. bovis infection in these environments. That is, M. bovis infection will progressively disappear from these ferret populations if the source of inter-specific transmission is eliminated. The estimates of Ro for M. bovis infection in South Island ferret populations were above one (the level required for disease establishment) for a number (5/10) of populations, though the imprecision made it impossible to ascertain whether Ro was significantly greater than one. The estimated threshold population density (Kt) for disease establishment was 2.9 ferrets km-2. It is inferred that, given sufficient population density (>Kt), the rate of intra-specific transmission of M. bovis among ferrets is sufficient for the disease to establish in ferrets in the absence of interspecific transmission. In these areas, ferrets would be considered maintenance hosts for the disease. Active management (e.g., density reduction or vaccination) of ferrets would be required to eradicate M. bovis from ferret populations in these areas, in addition to the elimination of sources of inter-specific transmission, particularly brushtail possums.