Food of the Opossum Trichosurus Vulpecula in Pastoral Areas of Banks Peninsula, Canterbury
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10 GILMORE: FOOD OF OPOSSUM JUDAY, C, 1940. The annual energy budget of an inland connection with valuation of the Danish waters from lake. Ecology 21: 438-450. 1883-1917. Rep. Danish Bioi. Sta. 25: 1--62. LACK, D., 1954. The natural regulation of animal num- SHELFORD,V. E., 1913. Animal communities in temperate bers. Clarendon Press, Oxford. America. Bull. Geogr. Soc. Chicago 5: 1-368. LOTKA, A. J., 1925. Elements of physical biology. (Reprinted 1937, Univ. Press, Chicago.) Williams & Wilkins, Baltimore. SOLOMAN, M. E., 1964. Analysis of process in control NICHOLSON, E. M., 1957. Britain's nature reserves. of insects. In Advances in ecological research, vol. Country Life, London. 2. Ed. Cragg, J .B. Academic Press, London & New York. (A critical evaluation of work done on insect ODUM, E. P., 1959. Fundamentals of ecology. 2nd population dynamics and controL) edition. Saunders, Philadelphia & London. TALBOT, L. M., and TALBOT, M. H., 1963. The high PARK, T., 1962. Beetles, competition and populations. biomass of wild ungulates on East African savanna. Science 138: 1369-75. (A compact summary of a vast amount of work.) Trans. 28th N. Amer. Wildlife Conf.: 465-76. PEARSALL, W. H., 1964. The development of ecology in THIENEMANN, A., 1926. Limnologie. Jedermann, Breslau. Britain. Brit. Ecol. Soc. Jubilee Symp.: 1-12. (With a valuable list of references.) VARLEY, G. c., 1947. The natural control of population balance in the knapweed gallfly (Urophora jaceana), P.E.P. [Political and Economic Planning], 1955. World J. Anim. Ecol. 16: 139-87. population and resources. Allen & Unwin, London. WYNNE-EDWARDS, V. c., 1962. Animal dispersion in PETERSON, C. G. J., 1918. The sea bottom and its pro- relation to social behaviour. Oliver & Boyd, Edin- duction of fish-food. A survey of work done in burgh & London. FOOD OF THE OPOSSUM TRICHOSURUS VULPECULA IN PASTORAL AREAS OF BANKS PENINSULA, CANTERBURY D. P. GILMORE Zoology Department, University of Canterbury". INTRODUCTION OpOSSUIllS are very numerous on Banks Peninsula. By day they often shelter in such Previous work on the foods of the brush- places as gorse hedges, old willows, macrocarpa tailed opossum (Trichosurus vulpecula) in shelter belts and rock crevices, and emerge at New Zealand has been concerned with the night to forage in nearby fields; they also cause choice of plants taken in indigenous bush. much annoyance by raiding gardens and Although clover was sometimes recorded as a orchards. preferred food the conclusion was reached that Much of Banks Peninsula is rugged with opossums "are not grass-eating animals" many peaks up to 2500 ft. and ample cover is (Mason 1958), and that "the opossum is not, available on the rocky hillsides. Although the and will never become an important grassland pest" (Howard 1963). peninsula supports large dairy and beef cattle herds as well as many sheep, there is still Present research on Banks Peninsula, Canter- much bush including totara (Podocarpus bury, from November 1963 to August 1964 totara), lacebark(Hoheria angustifolia), konini shows that although opossums appear to be more (Fuchsia excorticata), fivefinger (Neopanax numerous close to favourable bush, they often arboreum), and mahoe (Melicytus ramiflorus). occur many miles from any native or exotic The original bush is now mainly restricted forest. U llder these circumstances opossums to gullies, shaded slopes and scenic reserves, feed largely, if not exclusively, on plants serv- although there is some secondary growth. ing as food or shelter for domestic stock. Clover, . This work is part of a Ph.D. study carried out under grass and pasture plants form a large part of the tenure of a Research Fund Fellowship of the their diet throughout the year. University Grants Committee. GILMORE: FOOD OF OPOSSUM 11 There are many places alongside the roads on and Birdlings Flat on the Peninsula, and Dun- the peninsula with small patches of bush, sandel, Methven and Woodend on the Canter- mainly five finger, konini, mahoe, broadleaf bury Plains. (Griselinia littoralis) and manuka (Leptosper- The Banks Peninsula Rabbit Board began mum scoparium), which provide both shelter operations against the opossum in the Kaik and food for the opossums. Gorse (Ulex Lighthouse area on the south-east side of the europaeus) is very widespread and such peninsula ;n July 1963, and regular collec- exotics as willow (Salix spp.), pines (Pinus tions of animals destroyed by the Board began spp.), poplars (Populus spp.) and macro- in the following November. The Board uses carpas (Cupressus macrocarpa) are very com- cyanide, followed by dogs, trapping and shoot- mon. ing with spotlights to reduce the opossum Banks Peninsula has a mild climate well population. suited for farming. The mean annual rainfall By visiting the area once a month where the recorded at Akaroa is 43 in. and the mean Board was operating~ a number of opossums annual temperature 46°F. were collected, weighed, measured and dis- sected. The amount of food eaten by an METHODS OF STUDY opossum varied with the size of the animal, but the average weight of the stomach con- Most of the opossums obtained for this study tents of 100 animals was 4.3% of the body came from Banks Peninsula (Fig. 1), and all weight. were from pastoral lands where pasture plants were readily available for food; most of the STOMACH CONTENTS paddocks have been oversown with introduced grasses. The stonlach contents contained a surpris- ingly high proportion of grass and clover, these two often being the only plants present. Grass was frequently eaten, even when many other plants including konini and fivefinger were available; "dandelion" flowers were also very often eaten particularly in summer and autumn. Tables 1 and 2 show the foods occurring regularly in the stomachs of the animals BANKS PENINSULA examined. TABLE 1. Pasture plants recorded in the stomachs of 217 oppossums. Frequency of Plant species occurrence LEAVES Grasses Sweet vernal Anthoxanthum odoratum 2 Meadow grass Poa pratensis 3 Ryegrass Lolium perenne 25 FIGURE 1. Map of Banks Peninsula, the main Cocksfoot Dactylis glomerata 10 collecting area for this study. Unidentified specIes 116 Of the opossums collected from the peninsula Total grasses 156 most came from the vicinity of Pigeon Bay White clover Trifolium repens 100 and the roads about Hickory and Le Bons Bay "Dandelion" ..".. ...". 18 Yarrow Achillea millefolium 3 along which are extensive areas of pasture, Sorrell Rumex acetosella 3 small patches of bush and many acres of gorse. FLOWERS 47 Blackberry and broom are less common. About "Dandelion" ".". the farmhouses there are usually orchards and White clover ..".. 5 SEEDS shelter belts of pines and macrocarpas while Grasses, unidentified spp. 9 willows grow along many of the streams. A White clover P'__' 2 smaller number of opossums was picked up NOTE. "Dandelion" included unidentified spp. of yellow- from the roads about Motukarara, Tai Tapu llowering flatweeds of the family Compositae. 12 GILMOHE: FOOD OF OPOSSUM TABLE 2. Non-pasture plants recorded in the TABLE 3. Percentage of stomachs containing stomachs of 217 opossums taken in pastoral clover and grass. areas. Month N. D. J. F. M. A. M. J. J. A. Clover 33 27 36 55 7 42 52 60 56 83 Species Leaf Flower Fruit Grass 66 tOO 73 75 53 50 38 55 64 67 No. of Konini Fuchsia excorticata X X X animals Fivefinger Neopanax arboreum X examined 15 11 11 20 15 36 21 20 38 30 Muehlenheckia australis X Bush Lawyer Rubus spp. X Broadleaf Griselinia [ittora/is X In autumn many stomachs contained berries Lacebark Hoheria angustifolia X and fruit; "dandelion" flowers, earlier eaten Manuka Leptospermum scoparium X Mahoe Melicytus ramiflorus X very frequently, occurred far less often towards Totara Podocarpus tatara X winter. Matai Podocarpus spicatus X Pigeonwood Hedycarya arhorea X Table 4 shows the estimated proportion by Pokaka Elaeocarpus hookerianus X volume of the stomach contents made up by Poropara So/anum laciniatum X grass and clover for 78 animals collected during Coprosma spp. X June, July and August. In general clover was Myrtus pedunculata X Willow Salix spp. X eaten in larger quantities than was grass. How- Eucalyptus spp. X ever, the latter occurred more frequently in Macrocarpa Cupressus macrocarpa X X the stomach contents. Pine Pinus spp. X TABLE 4. Estimated volume of clover and grass in the stomach contents of 78 opossums. Konini and five fingers were highly preferred foods when available, and fruit and flowers were Estimated fraction Percentage frequency of stomach contents of occurrence readily eaten. Macrocarpa was found in many by volume Clover Grass stomachs in July and August, the staminate cones being especially favoured. Nil 13 24 Up to ¥4. 28 36 Y. to Yz 24 22 Yz to %. 23 9 Apples, acorns, walnuts, tomatoes and black- 12 9 berries were also found in the stomachs and a >% mushroom and a toadstool were each recorded Total 100 100 once. Only one stomach contained bark, and another the remains of six adults of the grass DISCUSSION grub Odontria sp. One animal taken in July Although it was previously considered that had eaten five faecal pellets. opossums do not eat grass in any quantity, an examination of the food of animals on Banks Where root crops were grown as winter feed Peninsula shows that this is not so. Opossums for stock opossums travelled long distances to graze frequently on grass and clover, through- feed on them. In Le Bons Bay there were well- out the year, even when other suitable foods defined tracks, often through long stretches of are plentiful, as they were in most areas from grass, made by opossums travelling from bush which the sample was collected. Opossums and gorse to feed on the crops. Many animals collected in January 1964 from Summerhill, killed in this area had swede, turnip and chou near Cust, as well as others from the roads in moellier in their stomachs.