Rabbit and fox introductions in Terra del Fuego: history and assessment of the attempts at biological control of the rabbit infestation

Published source details Jaksic F.M. & Yanez J.L. (1983) Rabbit and fox introductions in Terra del Fuego: history and assessment of the attempts at biological control of the rabbit infestation. Biological Conservation, 26, 367-374.
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Summary

Two pairs of European rabbits Oryctolagus cuniculus were introduced to the Chilean side of Tierra del Fuego island in 1936. Within a few years they had multiplied, the ground became riddled with holes and areas became denuded of vegetation. At the height of infestation (1953) rabbits numbered about 30 million. Attempts to control rabbits by hunting, trapping and gasing. Grey foxes Dusicyon griseus were released in a further control attempt in 1951 (three years prior to the myxoma virus decimating the rabbit population). Here, the potential success of foxes (including the native Patagonian fox D.culpaeus) as biological-control agent for the rabbits (and the wisdom of introducing grey foxes) is evaluated through analysis of diet.

In 1951, 24 grey foxes (this species did not naturally occur in Tierra del Fuego) were introduced from the adjacent mainland; the native Patagonian fox Dusicyon culpaeus was present butconsidered 'rather scarce'. The foxes (young animals of both sexes) were released near the village of Onaisin (Chilean Terra del Fuego).

The myxoma virus was introduced only three years after the foxes, and any effect of the initial fox introduction in reducing the rabbit population is unknown. A re-analysis of published and unpublished food data was made to assess if it was pertinent to introduce grey foxes. Additional data was collected between June 1977 and July 1978: 69 D.griseus were collected in 18 localities spread through the Chilean side of the Archipelago and seven D.culpaeus were from locality, stomach contents were assessed.

Of the vertebrate prey recorded, rabbits made up only 1.7% of the prey of D.griseus but comprised 20.0% of that of D.culpaeus. Rodents (two mouse species Akodon xanthorhinus and Reithrodon physodes, and Magellanic tuco-tuco Ctenomys magellanicus, Reithrodon physodes) made up 20.4% and 40.0%of the diets and birds 35.6% and 13.3% of the diets of D.griseus and D.culpaeus respectfully. Nether species were recorded as killing livestock (e.g. sheep) but both consumed carrion, D.griseus appearing more prone to scavenging.

The authors estimate that a single Patagonian fox should remove as many rabbits as 12 grey foxes per given area. They conclude that instead of releasing grey foxes, it may have been better to have introduced more D.culpaeus or to have managed their existing native populations to increase their numbers.

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