Gastric Emptying and Gastrointestinal Motility in Leach's Storm-Petrel Chicks (Oceanodroma leuchorhoa)

Abstract

-We used radiographic techniques to observe gastric motility during digestion of a meal in four Leach's Storm-Petrel chicks, 40-55 days old. A radio-opaque substance was added to the daily feeding for radiographic observation. We observed a biphasic gizzard contraction cycle with a frequency of 7.5 cycles/min. Gastric emptying occurred with each cycle and frequent intestinal refluxes were observed. Proventricular contractions were rarely observed; when observed, they affected only the ventral surface near the gizzard. Layering of proventricular contents, which we assumed to be a layer of dietary lipid over an aqueous phase, developed postprandially. Limited proventricular motility would favor layering; and ventral proventricular motility, along with regular gizzard motility, would promote gastric emptying of the more ventral aqueous layer. These observations are consistent with the idea that procellariiform are of dietary origin and that lipid accumulation in the stomach is linked to a unique gastrointestinal anatomy and motility. Received 21 March 1988, accepted 22 August 1988. PROCELLARIIFORM birds (albatrosses, fulmars, shearwaters, and other petrels) can store oil in their large, glandular and distensible fore-gut or proventriculus. The oil is found in both chicks and adults (Lewis 1966, Grubb 1971) and in birds captured at sea or on land. The oil was originally thought to be from the preen gland (Carter and Malcom 1927) or proventricular secretions (Matthews 1949), but is now considered to be of dietary origin (Imber 1976, Clarke and Prince 1976, Warham 1977, Jacob 1982). Cheah and Hansen (1970) proposed a mechanism for stomach oil formation in which low proventricular pH led to rapid breakdown of proteins and slow lipolysis, causing lipids to separate from the aqueous phase and accumulate. The heavy, more aqueous material settled and emptied first, followed by the lighter, oily lipid (Cheah and Hanson 1970, Warham 1977). This mechanism presumes that there is substantial layering of a lipid phase above an aqueous phase prior to proventricular emptying, and that the proventriculus must have limited gastric motility in order for the layering to persist. In humans, lipids empty from the stomach more slowly (14 ? 3% h-1) than aqueous (34.3 ? 1.8% h-W) or solid components (22 + 1.8% h-') (Jian et al. 1982), and some layering of lipids above nonlipids is found (Chang et al. 1968, Meyer et al. 1986). In birds, there are few studies that compare gastric emptying of lipid and aqueous components (Duke 1986a). Our objective was to describe for the gastric motility in a representative procellariiform. We specifically examined whether lipid accumulated above an aqueous phase in the proventriculus and whether a lack of motility in the proventriculus accounted for accumulation of oils. We chose Leach's Storm-Petrel chicks (Oceanodroma leucorhoa) as our representative procellariiform. The diet of Leach's StormPetrel chicks has a high (up to 60% of fresh mass) lipid content (Place and Roby 1986). We fed meals containing BaSO4 to storm-petrel chicks, and observed and recorded gastric motility cineradiographically. The observed gastric motility was considerably different than that previously described for other birds (Duke in press) and consistent with the accumulation of stomach oils in this species.