SOME FACTORS AFFECTING PRECISION OF THE TOTAL-BODY ELECTRICAL-CONDUCTIVITY TECHNIQUE FOR MEASURING BODY-COMPOSITION IN LIVE BIRDS

Measurement of total body electrical conductivity (TOBEC) is a simple non-destructive method for estimating total body fat in live birds. So me published validations of the TOBEC technique have been promising, b ut other results, especially from species less than 100 g live mass, h ave indicated that TOBEC measurements add little to the accuracy of bo dy fat estimates obtained with other nondestructive methods. We examin ed the accuracy of TOBEC body fat estimates for small birds by validat ing the technique on two passerine species, House Sparrows (Passer dom esticus) and European Starlings (Sturnus vulgaris). Lean mass explaine d only 57% of the Variation in TOBEC for sparrows (average mass: 28.4 g) and 74% of the variation for starlings (average mass: 83.7 g). TOBE C measurements were not sufficiently precise to detect even large (i.e ., 100%) changes in fat reserves of either sparrows or starlings. Thes e results, when compared with validations for larger species, indicate that the precision of body composition estimates from TOBEC is very s ensitive to subject size in relation to chamber size (coil diameter) o f the TOBEC instrument; precision is greatest for subjects that nearly fill the chamber. We confirm that accuracy of TOBEC estimates of body composition in a variety of bird species depends on developing specie s-specific calibration curves; precision of estimates depends on use o f a TOBEC chamber size appropriate to the study species.