Determination of Resting Metabolic Rates in Great Egrets (Ardea alba) and Snowy Egrets (Egretta thula) using Respirometry

Energy enters the body of an animal as food. Some of this energy is then used to satisfy the animal's metabolic functions and various activities. Attempts to quantify energy use and thus determine the costs of these activities often use basal metabolic rate (BMR) or resting metabolic rate (RMR) as an index. These rates occur during periods of minimal and low energy expenditure, respectively. In May 2018, we used respirometry to measure RMR for two Great Egrets (Ardea alba) and three Snowy Egrets (Egretta thula) captured on foraging grounds. The Great Egret mean RMR of 0.015 ml O-2/g/min represents the first record for this species. The Snowy Egrets had a mean RMR of 0.021 ml O-2/g/min, which was higher than the previously reported BMR. This discrepancy is discussed. Rates for both species were relatively stable over chamber temperatures that ranged between 24 degrees C and 39 degrees C.