Total body electrical conductivity (TOBEC) is a noninvasive method for the estimation of lean mass in live subjects. Lipid content can be calculated from the body mass measured and the lean mass estimated from TOBEC. I used live American Kestrels (Falco sparverius) to study the accuracy of this method. TOBEC measurements were compared to actual body content determined by Soxhlet fat extraction using petroleum ether as the solvent. TOBEC estimated 73.7% of the variation in lean mass in a sample of 21 kestrels. The use of restraining devices (Vetrap and cardboard cylinders) altered the TOBEC measurement but only by an average of 1.92% and 0.83%, respectively. TOBEC estimated 83.8% of the vii variation in lean mass for 21 kestrel carcasses warmed to 39.8°C. No significant difference was found between the slope or elevation of the calibration lines developed using live or dead kestrels. A significant difference was found between measurements taken at two different positions. Body temperature altered the TOBEC measurements by an average of 1.54% (SE = 0.55) for each 1°C change over a temperature range of 7.0°C (37.3-44.4). The calibration line developed for kestrels was used to estimate lean mass and compute fat mass of migrating kestrels, Sharp-shinned Hawks (Accipiter striatus) and Merlins (Falco columbarius). The average percent fat mass of kestrels trapped during migration at Cape May, New Jersey, was 6.01 % (SE = 1.92, n = 1 2) for males and 8.51 % (SE = 2.00, n = 13) for females. The difference in lean mass between male and female, and between early, mid-season, and late migrating Sharp-shinned Hawks differed significantly during migration. The fat mass of Sharp-shinned Hawks averaged 5.55% (SE = 0.94, n = 53) for males and 10.92% (SE = 0.80, n = 87) for females. Male Merlins had an average fat mass of 18.05% (SE = 3.35, n = 7) and females averaged 14.19% (SE = 3.15, n = 8).

Total body electrical conductivity (TOBEC) is a noninvasive method for the estimation of lean mass in live subjects. Lipid content can be calculated from the body mass measured and the lean mass estimated from TOBEC. I used live American Kestrels (Falco sparverius) to study the accuracy of this method. TOBEC measurements were compared to actual body content determined by Soxhlet fat extraction using petroleum ether as the solvent. TOBEC estimated 73.7% of the variation in lean mass in a sample of 21 kestrels. The use of restraining devices (Vetrap and cardboard cylinders) altered the TOBEC measurement but only by an average of 1.92% and 0.83%, respectively. TOBEC estimated 83.8% of the variation in lean mass for 21 kestrel carcasses warmed to 39.8oC. No significant difference was found between the slope or elevation of the calibration lines developed using live or dead kestrels. A significant difference was found between measurements taken at two different positions. Body temperature altered the TOBEC measurements by an average of 1.54% (SE = 0.55) for each 10C change over a temperature range of 7.00C (37.3-44.4). The calibration line developed for kestrels was used to estimate lean mass and compute fat mass of migrating kestrels, Sharp-shinned Hawks (Accipiter striatus) and Merlins (Fa/co co/umbarius). The average percent fat mass of kestrels trapped during migration at Cape May, New Jersey, was 6.01 % (SE = 1.92, n = 1 2) for males and 8.51 % (SE = 2.00, n = 13) for females. The difference in lean mass between male and female, and between early, mid-season, and late migrating Sharp-shinned Hawks differed significantly during migration. The fat mass of Sharp-shinned Hawks averaged 5.55% (SE = 0.94, n = 53) for males and 10.92% (SE = 0.80, n = 87) for females. Male Merlins had an average fat mass of 18.05% (SE = 3.35, n = 7) and females averaged 14.19% (SE = 3.15, n = 8).