Evaluation of the Cyclopropane Absorption Method of Measuring Avian Body Fat

Abstract

-The mean absolute percent error of predicting the fat mass of 40 Rock Doves (Columba livia) by the cyclopropane absorption method was 11%. A sensitivity analysis of some of the 15 variables used in computing fat mass by the cyclopropane absorption method showed that: (1) cloacal temperature was a good measure of body-fat temperature, (2) the lipid solubility coefficient of cyclopropane reported for rats was appropriate for pigeons, (3) minimum error occurred with an animal density of 1.08, (4) error was relatively insensitive to a range of reasonable estimates of body water, and (5) the most accurate method of measuring chamber volume was unclear. We list advantages and disadvantages of this user-unfriendly method and provide recommendations for future users. This method does not require a calibration based on fat extracted from dead birds; the accuracy and precision of a system assembled to measure the fat mass of live birds can be evaluated with olive oil standards. The accuracy of estimating fat mass of a living bird seems to be dictated, in large part, by the analytical equipment and procedures used rather than by the bird. Received 14 April 1997, accepted 21 July 1997. THE LACK OF AN ACCURATE nondestructive or noninvasive technique for determining whole body-fat storage is one of the greatest hindrances to studies of avian ecological energetics. Fat, which has an energy content of about 2.5 times that of protein or carbohydrate per unit dry mass and about 8 times per unit wet mass, is the main energy store in birds (Pond 1981, Blem 1990). Mass of body fat (FM) is one quantitative measure of a bird's preparedness for successfully completing an energy-demanding activity such as migration or egg laying and surviving such energy-demanding periods as: (1) prolonged starvation (Cherel et al. 1987), (2) summit (peak) rates of energy metabolism during a severe winter period, or (3) an unseasonably cold storm during a nonwinter period (see Gessaman and Worthen 1982, Elk-