Biology and Control of Feral Pigs on Isla Santiago, Galapagos, Ecuador

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Abstract
(1) Feral pigs (Sus scrofa L.) on Isla Santiago, Galapagos, have an adverse effect on several endemic animal species. (2) Pigs were commonest in the higher elevations (> 250-300 m), especially near succulent green forage and water. The population was estimated at 2000-3000. (3) Average home range for seven adult pigs (four male, three female) was 1.28 km2 (S.E. = 0.36, range 0.20-2.88 km2). Pigs living near xeric communities extended their ranges into these areas after El Nino rains stimulated abundant herbaceous growth. (4) Pigs bred throughout the year. Monthly pregnancy rates for sows ranged from 25 to 78% and mean number in a litter was 4.7 (S.E. = 0.3, range 1-10). Estimated piglet mortality in the first 19 weeks after birth was 52%. (5) Pigs were extreme generalists. Forbs were the major food, with grasses, fruits and invertebrates consumed in moderate amounts. Pigs had little apparent effect upon native vegetation, probably understorey communities evolved under heavy use by the native giant tortoise. (6) Based on cost and efficiency, poisoning was the best method of control. Shooting was moderately effective but trapping and snaring were ineffective. (7) The minimum recommended control is eradication of pigs in all sensitive areas and in buffer zones surrounding these areas.