Feral Goats on Raoul Island. I. Effect of Control Methods on Their Density, Distribution, and Productivity
- Protection Forestry Division, Forest Research Institute, P.O. Box 31-011, Christchurch, New Zealand
Goats were liberated on Raoul Island early in the 19th century. Attempts to eliminate the goats commenced in 1937 and have accounted for at least 15 000 animals. Since 1972, when annual hunting expeditions began, both the number of goats and the area over which they range have steadily declined and the herd is now almost extinct. Despite these changes, the mean group size of goats in 1981-83 remained the same at 3.19, 2.74 and 3.24 respectively. On average, 19% of goats escaped each encounter with the hunters. The breeding season extended from January-September, with most activity in April-June. Productivity of the herd has increased by 77% since 1972, presumably in response to an improving food supply. This increased productivity has been achieved by an increase in the frequency of breeding from an average of 0.83 times/year in 1972 to an average of 1.08 times/year since 1981, increases in breeding rates of young females, and in mean litter sizes of older females. These parameters, and the primary sex ratio of 49:34, are used to calculate an estimate of exponential birth rate of 0.529.