Opossums Vie With Farm Stock

Press, Volume CIII, Issue 30633, 26 December 1964, Page 5

Opossums Vie With Farm Stock

[Specially written for “The Press’’ by

D P GILMORE,

Department of Zoology,

University of Canterbury!

r FHE opossum, first introduced into New Zealand around 1840, ! is at present the focus of attention. The damage it causes to native bush and in the new exotic forests is causing great concern.

Few people realise, however, that the opossum is as much a pastoral grazer as a tree-browser, and may, in some districts, seriously reduce the carry ing of the land, consuming food that would otherwise be eaten by stock.

Opossums were originally brought into New Zealand from Australia to enhance the bush and provide a revenue for the country from the sale of skins.

Increase in opossum numbers and spread was at first slow and complete for partial protection was given to the animals until 1946.

Because of growing public pressure for some control other than that resulting from the sale of skins a drastic change was brought about in 1947. Most Areas The requirement of licences and permits to trap opossums was then abolished. It was made illegal to liberate the animals and poisoning was allowed ir certain areas where depredations were particularly severe.

In 1950 a bounty of 2s 6d a head was placed on the opossum. This has since been abolished but in many areas rabbit boards have now taken over responsibility for the destruction of the animal.

Today, the opossum may be found in most parts of the country, contrasting with the other introduced marsupials, wallabies, which are found only in restricted areas close to the original sites of liberation.

Until recently it was assumed opossums fed almost exclusively on trees and shrubs. Willows were damaged and orchards and gardens suffered. But the opossum was not considered to affect directly the carrying capacity of the land, as the rabbit does. Now research being undertaken at the Zoology Department of Canterbury University is showing that this charge may also be laid against the opossum. Eat Clover Opossums may often be seen scuttling across the roads and grazing alongside cattle and sheep at night. They readily eat clover and dandelion and like cocksfoot and ryegrass. Swede and lucerne patches attract large numbers of opossums. Since 1962 the Banks Peninsula Rabbit Board has been undertaking a campaign of opossum destruction. Using poison, dogs and traps a gang of men under the supervision of Mr J. Phillips, of Akaroa, are systematically working their way around the Peninsula. Since the campaign began many thousands have been destroyed. With the board’s co-opera-tion research workers each month visit the area in which the gang is working to gain first-hand knowledge of the type of country and the vegetation. A large sample of opossums is collected for dissection in the laboratory. Pound A Night The examination of more than 700 opossums in the last year, most of them from the peninsula, has clearly demonstrated that opossums favour clover and grass as much as konini and fivefinger, not only when other foods are scarce, but in large quantities throughout the year.

A large opossum will eat up to a pound of food a night. Most opossums reach a weigth of 8 to 9 pounds, compared with a rabbit’s four pounds, and a hare’s seven pounds. Hares and rabbits eat far less than opossums and it has been estimated seven rabbits eat as much as one sheep. Opossums may also seriously reduce the carrying capacity of the land by selecting only the best clovers and grasses and it is probable their urine poisons the herb age.

I During the day opossums I shelter in gorse thickets, ! macrocar pas and hollow wililows, emerging at night to forage in nearby fields. i Many paddocks have wellworn tracks, along which [opossums scamper at night to ttheir feeding and playing areas. These tracks are often as well-defined as any sheep track winding around the side of a hill.

Pastoral grazing is true not only for extensive areas of farmland. Clover and grass along the edge of a forest or in a bush clearing are readily eaten.

Opossums in the heart of the Ureweras have been found to feed on the clover alongside the road. Those nea rthe bush and pakihi regions of Buller and in the high country of Marlborough will eat pasture if it is available. Huge Sums Since large-scale destruction of opossums has begun collossal sums of money have been spent on control. At present none of this is recovered directly. This seems unfortunate because although many carcases are irrecoverable, some of the capital outlay could be recovered by the sale of skins. Opossum skins vary from chestnut-brown through a number of darker shades to silver and blue-grey, the most valuable. Opossum meat is quite palatable and would have an unlimited market as pet food and possibly, it could be exported. How much damage does the opossum cause in pastoral land? yet there have been too few' scientific investigations to make a full evaluation of the opossum's economic status. Certainly the opossum will never become the same problem as the rabbit. Instead of a litter, only one young is born to the opossum, generally in late autumn after a gestation period of 17-18 days. The new-born “joey," about

( -Uie size of a honey-bee, makes | its way to the mother’s pouch, [attaches to the teat, and remains there for several months. When 5-6 months old and the size of a young kitten. the joey leaves the pouch and rides on its mother's back. It can now feed itself ; but it may remain with the [mother until it is a year old. I If conditions are favourable a second joey may be ■ born in late spring. Few Twins | The event of twins is so [rare as to be scarcely recorded. However, in November last, Mr R. Le Valliant, [of the Peninsula Rabbit Board, noticed a silver-grey female carrying two large joeys on her back and another much smaller attached to the teat. Although autumn and spring are the periods when most joeys are born, they may appear in other months of the year, if, for example, the first-born joey dies. Control or eradication? Opossums can be controlled in many areas. They travel on well-defined tracks and feed and play on certain trees. This makes them easy to trap and shoot. Dogs readily scent out the dens and root out the occupants. Curiosity and hunger cause the opossum to fall a ready victim to cyanide and 1080. Here To Stay

Opossums are, therefore, not hard to control in certain areas. But much greater problems are faced in attempting control in extensive regions of bush and forest. Eradication? This is a different story. The opossum is so widespread and inhabits such rugged and inaccessible country that he is undoubtedly here to stay. This fact must be faced and taken into account in any large-scale and long4erm campaigns. It is physically and economically impossible with our present knowledge to aim for the last opossum. Along with deer, pigs, and goats the opossum will be with us for many years yet.