Captures, Body Mass and Diet of Platypuses in a Subalpine Tasmanian Lake.

Abstract

Studies into the ecology of the platypus have concentrated on populations inhabiting !otic waters on mainland Australia. This paper presents preliminary results of a study into the feeding ecology and energetics of the platypus in a subalpine lake in Tasmania. During the autumn, winter and early spring months 29 individual platypuses were captured (13 adult females, 13 adult males and 3 juveniles). Of these, 46% of the adult males, 31% of the adult females and one of the juveniles were recaptured between one and eight times. Catch per unit effort was similar for the 1800-2400hrs, 0600-1200hrs and 1200-1800hrs time periods (0.158, 0.161 and 0.156, respectively). However catch per unit effort was low (0.057) between 2400hr and 0600hrs. There was no significant difference in the mean body mass of adult males and females between autumn, winter and early spring, however the condition of the females, indicated by the tail fat index, decreased in early spring. The overall mean body mass for adult males and adult females caught during the autumn/winter and early spring months was 2293.21g ± 300 (1920-2740g) and 1375.22g ± 147 (1150-1580g), respectively. This supports the observation that platypuses in Tasmania are larger than those occurring in mainland water bodies. The timing of juvenile captures suggests that matings occur at Lake Lea between mid September through to January. This indicates that the breeding season may be later in Tasmania than on the mainland. The contents of cheek pouches were collected from individuals caught during the autumn, winter and early spring months for identification of food items. Food items identified so far include Trichoptera, Gastropod molluscs, Ephemeroptera nymphs, Coleoptera larvae and Diptera, with Trichoptera forming the dominant food item. Measurements of the daily energy expenditure of six adults were attempted during late winter and early spring using the doubly labelled water technique.