Evaluation of the TOBEC Method for Calculating Fat Mass in Tree Sparrows Passer montanus and House Sparrows Passer domesticus

Abstract

Total body electrical conductivity (TOBEC) is the name of a non-invasive method for investigating total body fat (TBF) in vertebrates. The error of measurement depends on body mass (for large animals the relative error is small), body shape and other factors. The ACAN-2 apparatus operating on the basis of the TOBEC method shows integer numbers (readings) correlated with lean body mass (LBM). From the series of these readings (measurements) TOBEC can be calculated in many ways. The error for LBM and TBF measurements in Tree Sparrows (of masses 22.5 ± 1.7 g) and House Sparrows (of masses 29.8 ± 2.0 g) was 1.19 g. This error may be reduced by repeating the TOBEC measurement and calculating the arithmetic mean of readings from the apparatus obtained 1 second after the commencement of measurement. Readings making up a single measurement series showed periodic irregular fluctuations of average amplitude 3 units in the case of Tree Sparrows and 5 units for House Sparrows - corresponding to errors of 0.5 g LBM in both species. Given individuals of both species were characterised by similar differences between the first and second TOBEC measurements. The TOBEC value obtained in a measurement during which a bird defecated in the chamber of the apparatus was significantly higher than that for a bird in a clean chamber. The orientation of the head in the chamber did not influence the repeatability of the TOBEC measurement. In Tree Sparrows, the relationship between TOBEC and LBM differed between those captured and held for one night prior to measurement and those measured for TOBEC immediately after capture.