NUTRIENT RESERVES AND THE ENERGETICS OF REPRODUCTION IN AMERICAN COOTS

To investigate the bioenergetics of reproduction in American coots (F. americana) 108 males and 93 females were collected at Delta Marsh, in southern Manitoba [Canada], in 1981. Prenesting and nesting birds were analyzed for fat, protein, and ash content in the nonreproductive tissue. For females, these values were compared to the nutrient requirements of the reproductive tissue during egg-laying. Feeding conditions before arrival can affect subsequent reproductive output. Fat reserves may function as a threshold that influences the initiation of breeding; protein reserves and time of arrival influence the timing of a nesting attempt. Territory quality is important and it can result in the termination of laying before nutrient reserves are depleted. By distributing costs of clutch formation before (through nutrient storage) and after (through increased biparental care of eggs and young) clutch formation, the required energy intake concurrent with egg-laying is substantially reduced in female coots.