The ability of feral goats to become pests is partly a consequence of the process of domestication. Neolithic people selected biological characteristics from wild goats, such as higher intrinsic rates of increase and increased sociability that have resulted in their domestic descendants becoming a particular nuisance when they escape to become feral. Feral goats live in about 11 % of New Zealand, mostly on land reserved for conservation of the indigenous biota. Their uncontrolled densities are usually less than 1 ha-1, but have reached 10 ha-1 in one area.
A common question that arises when considering the results from a well-designed sampling programme for a rare or invasive species is: ‘Sampling has failed to detect a species that could have been present, so can we calculate the probability that it truly was absent during the sampling period?’ Noting that this invokes a Bayesian view of ‘probability’, which therefore must be accepted if the question is to be answered in the affirmative, we present a method of addressing it.