• ~. • } .' · ' I I I :- •• ) .!,... ... I .. ,, / / . ... ·- -- . rlf!!!!>. - , . ~ i >) . ~~ ' • . ,. .. '-" _.,, / . • i Al • ) . I .. , /.:.~ I '} / ... ' fi('r. ( ~ r· ,, ,, I ..,.: _. ( I f i I ,. I ·r· : .. I 1 ' ECOLOGICAL ENERGETICS AND REPRODUCTION IN THE COMMON RINGTAIL POSSUM, Pseudocheirus peregrinus (MARSUPIALIA: PHALANGEROIDEA) by / Sarah Ann Munks B.Sc.. (Hons), U.C.N.W, N.WALES ·' Submitted in fulfilment of the requirements for the degree of Doctor of Philosophy, Department of Zoology, University of Tasmania, Hobart, Tasmania, Australia January 1990 Frontispiece from 'Ferdinand Bauer, The Australian Natural History Drawings' (page 28) by Marlene J. Norst (1989) published by Lothian Publishing Company Pty Ltd, Sydney. ·' DECLARATION This thesis contains no material which has been accepted for the award of any other degree or diploma in any University, and, to the best of my knowledge and belief, contains no copy or paraphrase of material previously published or written by another person, except when due reference is made in the text of the thesis. Sarah Munks ABSTRACT This study examines the annual cycle of energy and time expenditure in a small folivorous marsupial, the common ringtail possum, Pseudocheirus peregrinus. Particular attention was given to the energy expended in lactation by the females. Field metabolic rate (FMR) and water flux were measured using an isotopic technique (doubly labeled water). Feeding rates were estimated from measurements of FMR in conjunction with information on the composition of the diet and a digestibility study. FMR's and subsequent feeding rates estimated by the doubly-labeled water technique do not include the proportion of food consumed which is diverted to milk solids and is not metabolised by the mother. The amount of energy transferred directly to the young ringtail possum via the milk was estimated from measurements of milk composition and production. Reproduction in the common ringtail possum in Tasmania was seasonal, with the majority of births (mean litter size 1.8) in late autumn and early winter. In general, the young leave the pouch during early spring and are fully weaned by the early summer months. There was no significant seasonal variation in the energy expenditure or water influx of males. The mean FMR of males and non-lactating females was approximately 2.5 times basal metabolic rate which is consistent with the hypothesis that a low total energy cost of free existence (or field metabolic rate) is a characteristic shared by arboreal folivores. Females showed significant changes in water influx and energy expenditure according to their lactational status. The greatest metabolisable energy expenditure was that of females during Phase 3 of lactation (30% above non­ reproductive metabolism). Water influx was correspondingly high in these females (36% above non-lactating females). In general, ringtail possums in both the field and captivity lactated for approximately seven months. However, the length of lactation was shorter in females which bred twice in a year. The composition of the milk varied throughout lactation. A peak in milk solids and energy content coincided with emergence of the young from the pouch. Milk solids represented around 18% (w/w) with milk fat representing only 10% of milk solids. Milk production peaked during Phase 3 of lactation. The dilute milk with a relatively low fat content combined with a long period of lactation result in slow growth of the young. Peak milk energy output was 154.5 kJ.kg-0·75 .d-1 and peak metabolisable energy allocation during lactation was 763.2 kJ.kg-0.75 .d-1. These were lower than values available for other herbivores. However, the total output of milk energy by ringtail possums ( 11 MJ/kg) and total metabolisable energy allocation during reproduction (23.4 MJ/kg) were similar to estimates available for other herbivores. The lactational strategy of the ringtail possum has been selected, most likely, in order to spread the energy demands of reproduction over time due to constraints on the rate of energy intake imposed by a leaf diet. The total energy requirement for reproduction ii (34.4 Ml/year, or 14% of total annual energy budget) suggests that the ringtail also has a relatively low overall energy investment in reproduction. Estimates of total body water made from isotopic dilution and measurements of body mass suggest that females utilise body fat stored during the early stages of lactation to cope with the additional energy required for late lactation. However, reproduction is apparently timed such that late lactation coincides with the increased production of young foliage. Therefore females may also increase their food and water intake during late lactation by consuming young foliage. Differences were found in the composition of milk collected from wild and captive animals. Chemical analyses of the leaves eaten suggested that these differences were due to variations in diet composition. It was, therefore, proposed that the intra­ and inter-population variation in reproductive traits shown by the common ringtail possum may be related to variations in milk composition and/or production caused by variations in diet quality. iii ACKNOWLEDGEMENTS I would like to express my sincere thanks to the following people who assisted me during the course of this project: My supervisors, Dr. B. Green, Dr. R. Rose and Dr. S. Nicol, for their guidance, advice and constructive criticism during the development and writing up of the thesis. The Commonwealth Scholarship and Fellowship Plan, Ingram Trust Fund and C.S.I.R.O I University Research Grants for financial support. The Department of Lands, Parks and Wildlife for their cooperation with permits and advice. In particular, Nigel Brothers for introducing me to the ringtail possum, Peter Mooney for helping me find a suitable study area, Nick Mooney for providing information on predation of ringtail possums by raptors and Steve Harris for identifying vegetation in the study area. Property owners, Peter and Garry Blunstone and H.C. Gavin for allowing me to carry out my field work on their land and Mr R. Bender for making his 'Ute' available use on the Island. Particular thanks go to Keith Newgrain, Steve Cork and John Libke at the C.S.l.R.O, Division of Wildlife and Ecology, Canberra for their time, guidance and assistance with milk analyses, isotopic technique procedures and analyses, and leaf composition analyses. Kevin Nicholas and Marion Loughnan, C.S.l.R.O, Division of Wildlife and Ecology, Canberra for performing the electrophoresis of whey proteins and Mike Messer, University of Sydney for the qualitative analysis of milk carbohydrates. 'TIM All those who assisted in the field work, including Sandra, Kathy,,.Mathew, Stephanie, Brian, Adam, Jean, Don, Jane, Ivor, Duke, Beccy, James and Michael. In particular, Steve Reid, Peter Serof, Kevin Hayde and Rick for coming back for a second dose of possum piss! The academic and technical staff in the Zoology Department, Uni of Tasmania. In particular, Barry Rumbold, Ron Mawbey for photography, Richard Holmes for being able to make or mend anything, Kit Williams for instructing me in the use of radio-telemetry, constructing computer programmes and general advise on computer techniques and Dr Adrian Bradley for constructively criticising the final chapter. Dr. Alistair Richardson and Dr. Glen McPherson for advice on statistical methodology Dr Woodward, Dr. P. Cowan, Dr. H Dove, Dr B Foley, Jim Merchant and Don Hird for advice and discussion on various aspects of the study. Dave Jacobs for his friendship and allowing me to use the outdoor enclosures. The Animal house staff and John and Stephanie Kalish for caring for my captive animals while I was away on field trips. Dr. Colin Stahel for his frienship, discussions and advice on measurements iv of standard metabolic rate and for his cartoons. My fellow students for their inspiration, friendship and encouragement. In particular, Rosemary Gales for much needed advice on isotopic techniques and for providing constructive criticism on Chapter 6, David Pemberton for introducing me to field procedures and Jean Jackson, Jane Pickard and Vaughan Monamy for their invaluable help in the latter stages. Very special thanks go to Mr Derek Smith for all his help throughout the study, in particular for putting up with me, Comish casserole, numerous field assistants and assorted orphaned marsupials invading his home at regular intervals. Thanks also go to Garth Smith for his technical assistance with radio-telemetry gear and photography. Anyone else my poor memory has failed to recall! Finally, Captain Rick and my parents who have always given me encouragement and support when needed. TABLE OF CONTENTS Abstract Acknowledgements 111 CHAPTER 1 GENERAL INTRODUCTION 1 CHAPTER 2 DISTRIBUTION, DESCRIPTION OF THE STUDY AREA AND GENERAL METHODS 7 2.1 Distribution of Pseudocheirus peregrinus in Tasmania 7 2.2 Study Area 8 2.3 Climate 10 2.4 Field Methods 10 2.4.1 Catching programme 10 2.4.2 Handling and measurements 11 2.5 Ringtail Possums in Captivity 12 2.5.1 Collection, maintenance and release site 12 2.5.2 Deaths and diseases in captivity 13 CHAPTER 3 GROWTH AND REFRODUCTION OF THE COMMON RINGT AIL POSSUM IN TASMANIA 15 3.1 Introduction 15 3.2 Methods 16 3.2.l Study Area and Animals 16 3.2.2 Growth Measurements 16 3.2.3 Age Estimation of Sucklings 17 3.2.4 Growth Rates 18 3.2.5 Development and Phases of lactation 20 3.2.6 Reproductive Status 20 3.2.7 Population Size 21 3.2.8 Statistical Methods