FOOD PROVISIONING BY WHITE-TAILED TROPICBIRDS - EFFECTS ON THE DEVELOPMENTAL PATTERN OF CHICKS

Food provisioning of Phaethon lepturus chicks by their parents was studied at Cayo Luis Pena, Puerto Rico. The interval between feedings delivered by an individual adult was more variable than food payload mass (higher coefficients of variation), and there was no day-to-day relationship between the feeding interval and feed mass. Adults demonstrated the ability to lift and transport food payloads substantially larger than the mean feed mass. Energetic considerations suggest that there is strong selection for parents to decrease the feeding frequency and increase feed mass, to some limit imposed by either the limits of the parents' delivery capabilities, or the limits of the chick's food receiving (swallowing) capabilities (the volume a chick can ingest in one feeding bout). In fact, the limits of the chick's swallowing capabilities occur well before the parents' delivery limits are reached, and thereby set the feed mass at a weight and volume that is easily within the adults' lifting and transporting capabilities. The mean feed mass is viewed as reflecting a particular "target' payload mass that parents strive to collect as quickly as conditions, and their own individual foraging abilities, will allow, and is a practical compromise between the short-term interest of the chick and those of the adult. While paretns are able to collect an abundance of food for their single chick, their pelagic foraging creates an intermittent, or "feast or famine' feeding situation for the chick, which promotes the characteristic developmental pattern of slow growth and large fat accumulations. -from Author