Feral Goats—Designing Solutions for a Designer Pest
- Manaaki Whenua - Landcare Research, P.O. Box 31011, Christchurch, New Zealand
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. The total population is estimated to be at least 300 000, which makes them the most common free- living ungulate in New Zealand. Most populations breed throughout the year, but show distinct Peaks of activity in summer and for some populations again in early winter. Most populations show a distinct decline in breeding in late autumn to mid spring. Annual birth rates can be high, up to 1.42 kids per female in the study populations. This is achieved by breeding twice within the year, breeding at an early age (as young as 6 months), and often producing twins and triplets. Feral goats are highly selective in what they eat, but have the ability to switch their diets as the more palatable food species are eliminated from their habitat. All these characteristics make goats particularly problematic pests on the conservation estate. However, domestication did not tum the goat into a complete r-strategist, boom-bust pest. Unharvested feral populations in New Zealand form dynamic K-strategist relationships with their resources that are stable, at least in the short term. This means their impacts are chronic, but the relationship can be manipulated to favour the resource if management can be applied ''chronically'', i.e., as sustained control. The Department of Conservation has attempted to organise its control actions in the highest priority areas either to eradicate goats where possible or to sustain control where eradication is not presently possible. An annual budget of $3.8 million was tagged for goat control in 1990-91. Since then, the Department has acted against goats in 146 areas, and successfully eradicated 14 populations. In 1992-93, 6160 hunter-days of ground control effort, and 230 hours of helicopter hunting effort were expended against feral goats, and 10.2 km of goat fencing was constructed. The effort was similar in 1991-92, and larger in 1990-91. The Department is attempting to ensure their control effort is maximised and sustained via a formal national control plan, and regional Conservation Management Strategies. If the present effort is maintained over the next decade, about half the feral goat populations now on the conservation estate are expected to be eradicated or controlled.