Is the Energy Cost of Begging by Nestling Passerines Surprisingly Low?

Abstract

McCarty (1996) reported that oxygen consumption rates (402) of resting and begging nestlings of five passerine species were little different and often equivalent. From this he concluded that begging is not a costly trait. In 1990, we obtained a similar result (Weathers and Anderson unpubl. data) with nestling Zebra Finches (Taeniopygia gutrata) using a more sensitive 402 method than McCarty's. We placed nestling Zebra Finches in a small-volume respirometer (350 mL) and employed open circuit respirometry coupled with the instantaneous method to determine 402 (Bartholomew et al. 1981). Despite finding negligible differences between the (tO 2 of begging and resting nestlings (less than a 5% increase over resting levels; n = 3), we were unable to conclude that begging had a low energy cost because we measured only one of the two processes by which animals utilize energy, namely aerobic metabolism. Most or even all of the energy that nestlings use when begging might be provided anaerobically, given the limited metabolic scope of altricial neonares (Weathers 1996). In anaerobic metabolism, which often is used to support short-duration, burst activities, ATP production does not involve oxygen consumption and resuits in the formation of lactic acid rather than water