Ferrets, Stoats, Weasels Found Decreasing

Press, Volume CII, Issue 30289, 15 November 1963, Page 26

Ferrets, Stoats, Weasels Found Decreasing

Ferrets, stoats, and weasels —the three species of mustelids present in New Zealand —all decreased sharply in numbers in both silands between 1948 and 1960, two years during which questionnaires were circulated, according to a booklet just published by the Animal Ecology Division of the Department of Scientific and Industrial Research. The booklet was written by Dr. W. H. Marshall, a Fulbright research scholar from the University of Minnesota, who worked with the division in 1960 and 1961. On the question of whether mustelids are, on balance, ‘‘good” or “bad,” when the amount of vermin they eat is measured against their effect on native birds, Dr. Marshall retains an open mind, though he says it is “more than probable" that the effects of the removal of the bush and the depredations of other introduced mammals on the birds’ food supply have outweighed the possible effects of mustelids on birds. Further research being carried out by a member of the division’s staff, Mr M. Fitzgerald, should throw more light on the matter, he says. Questionnaires were sent out by Dr. Marshall at the end of 1966 to about 500 persons, mostly field employees of Government agencies or local bodies. Four months later 272 replies had been received. The questions asked included the number of animate seen, the kind of food they were seen taking, and personal assessments &f the abundance of each species and whether they were increasing or decreasing. The answers were compared with the results of a questionnaire sent out in 1948 by Dr. K. Wodzicki, director of the division. “It appears that the numbers of all three species of mustelids have decreased sharply on both islands since 1948. There is an indication of a reduction in the distribution of the stoat on both islands, and of some restriction of weasel occurrence in tlie South Island. On the other hand, fewer persons reported no ferrets, which could indicate an increase in the area occupied by this animal on both islands,” Dr. Marshall says. Rabbit Control Dr. Marshall thinks the genera] reduction in mustelid numbers is connected closely with the success of

rabbit control during ths period. Stoats, however, are more adaptable in their foodsupply than ferrets or weasels, he says, and have been reported in large numbers during mice plagues; but the distribution and abundance of ferrets very closely parallels that of rabbits. Reports on feeding habits of the animals, and the examination of droppings and of the stomachs and intestines of carcases, indicated that introduced mammals and birds made up a large part of the "diet at stoats and ferrets. No figures are given by Dr. Marshall for weasels, presumably because these are generally rarer than the other species. Both stoats and ferrets were often seen feeding at carrion, especially after rabbit control operations. There was evidence of stoats feeding on crayfish at Ohakune, but a report of them taking spent salmon from the Poulter river in the Arthur’s Pass National Park was not confirmed. Experiments with 1080 poison fed to captive ferrets indicated that the animals might be poisoned through eating the carcases of deer or rabbits (but not rats) killed during poisoning operations. Dr. Marshall suggests that a way of controlling mustelids in bush areas might be to leave poisoned grain at trampers’ huts—which often harboured rats and mice on which stoats fed —or at deer carcases.