No abstract

The diet and habitat associations of bush dogs Speothos venaticus, categorized as Vulnerable on the IUCN Red List, are virtually unknown in the wild. In eastern Paraguay, bush dogs occur in the Reserva Natural del Bosque Mbaracayú. The Reserve contains one of the largest remaining fragments of the Interior Atlantic Forest in Paraguay as well as cerrado and grassland habitats. We analysed bush dog faeces to determine their diet. Bush dogs in the Reserve mostly ate vertebrates. Although small mammals (marsupials and rodents) were the most numerically dominant foods, agoutis Dasyprocta azarae and pacas Cuniculus paca represented 90.5% of biomass consumed. Cecropia fruit was also present in the diet. This is the first documentation of fruit consumption by bush dogs. Signs of bush dogs were detected in all habitats, with the greatest proportion in high forest.

Northern red-backed voles (Clethrionomys rUlilus) undergo a pronounced arumal cycle in body mass and are heaviest in summer and lightest in winter. We trapped voles throughout 1994 to determine how changes in body composition and organ size contributed to this cycle. Body mass peaked in summer for females and spring for males. Seasonal changes in body mass were primarily due to changes in lean mass. Body mass was 30-50% lower in winter than summer, and water content of lean mass was lowest in winter. Total body fat was low throughout the year but peaked (as with body mass) in spring (males) or early summer (females). Energy reserves in the fonn of fat depots are apparently most crucial during the breeding season. A low relative ash content in early summer was possibly due to a cation imbalance in the diet. Absolute and relative sizes of different body components contributed to the annual cycle in total body mass. All body components (except brown adipose tissue) declined in absolute mass, dry mass, and percent water during autumn, with skeletomuscular components contributing most to loss of total body mass. Most body components declined in proportion to declines in total body mass. However, liver, reproductive tract, and muscle mass of males declined proportionally more than total body mass; heart, brain, and bone declined proportionally less. Whole body analyses suggest that the annual cycle of body mass in C. rutilus is driven by seasonal changes in optimal body size. Component analyses are consistent with the hypothesis that the primary selective force driving seasonal changes in body components is the enhanced overwinter survival of C. rutilus with relatively small body size.

. 1997. Validation of two new total body electrical conductivity (TOBEC) instruments for estimating body composition of live northern red-backed voles Clethrionomys rutilus. Acta Theriologica 42: 387-397.Total body electrical conductivity (TOBEC) is a method for non-destructively estimating body composition. We sought to monitor seasonal changes in total body fat in northern red-backed voles Clethrionomys rutilus (Pallas, 1779), a microtine (10-45 g). We validated two new TOBEC instruments: the SA-3000 by EM-SCAN Inc. and the ACAN-2 by Jagmar Inc. Both instruments explained 94% of the variation in lean body mass and total body water. However, accuracy of fat estimates generated from lean mass predictions was poor for both instruments (± > 100%). Two instrument-specific multiple regression models and a TOBEC-free multiple regression model were used to estimate total body fat. All three improved the ability to predict total body fat in C. rutilus. These two TOBEC instruments can not be used to measure changes in total body fat of individual C. rutilus due to the small amount of fat reserves and lack of seasonal variation.