The natural enemy debate
Many pastoralists thought that ‘natural enemies’ (predators) would control rabbits more effectively than any other measure. New Zealand’s only native predators of rabbits were the swamp harrier (Circus approximans) and the weka (Gallirallus australis). Farmers saw mustelids – ferrets, stoats and weasels – as the most likely candidates, although others were considered.
There was a bitter debate in the 1880s about releasing mustelids. Some argued that they would have little effect in reducing the rabbit population, and would cause the extinction of ground-dwelling native birds. However, by the mid-1880s thousands had already been released. In fact, ferrets had official protection under the 1881 Rabbit Act as ‘natural enemies of the rabbit’.
Importing ferrets, stoats and weasels proved difficult – they were susceptible to distemper and many died in transit. In the early 1870s G. F. Bullen, a runholder from Kaikōura, shipped 600, all of which died. Of his next shipment of 700, only two ferrets and two weasels survived. In 1883, the government shipped 1,456 ferrets to New Zealand, but only 367 landed alive.
Despite the high death rates, importations continued through the 1880s. Government figures for 1884, 1885 and 1886 show that 18,333 ‘natural enemies’ were imported, but this was probably a conservative figure.
Mongoose on the loose
The introduction of a variety of predators for rabbit control was debated in the 1870s and 1880s. The American marten and the eagle were discussed, but not released. But a Kaikōura runholder released nine or ten mongooses in the mid-1870s, and the government let 16 loose in Southland in 1876. Other mongooses were liberated near Moa Flat in Otago. Fortunately, they did not acclimatise.
Breeding and releasing mustelids
Because shipping mustelids was difficult, the government and private individuals set up breeding stations. Richmond Brook and Flaxbourne stations in Marlborough bred and released about 800 ferrets a year in the 1880s. In 1888 the Amuri Rabbit Board liberated 1,000 stoats and weasels, 1,000 ferrets and 400 cats. The following year it released 600 stoats and weasels, 800 ferrets and 400 cats. In 1890 over 7,000 ferrets were released in Otago. A report in 1889 could not say how many had been released in Southland, because large numbers were bred and liberated privately.
A costly failure
From the 1870s to the turn of the 20th century, pastoralists and the Department of Agriculture enthusiastically supported using predators for rabbit control. However, opposition to the release of mustelids continued. In 1895 a columnist for the Otago Witness noted that ‘ferrets and weasels appear to be on the increase, but they do not as yet seem to have had much effect on the [rabbit] pest’. 1 Ten years later the same paper commented that ‘the ferret as a rabbit exterminator has been found of little value, while it is of much more harm in other directions’. 2 By then, mustelids had spread throughout the South Island.
Mustelids became a pest themselves, preying on native animals. Stoats in particular have had a devastating effect on native bird populations.