Investigations of the adaptive role of stomach oils in seabird reproduction

DANIEL D. ROBY AND JAN R. E. TAYLOR

Cooperative Wildlife Research Laboratory

AND Department of Zoology, Southern Illinois University 300 Carbondale, Illinois 62901-6504

ALLEN R. PLACE control 200

Center of Marine Biotechnology Cl) University of Maryland C/) Baltimore, Maryland 21202

0 x—fostered During the 1991-1992 austral summer, we investigated the 100 role of stomach oil in seabird chick development. Field research was conducted on Island, South Georgia (54 00S 3802W), in cooperation with the British Antarctic Survey. Daniel D. Roby stayed on Bird Island from 13 January to 3 March 1992; Jan R. E. prions Taylor from 13 January to 3 April; and Allen R. Place from 3 March to 3 April. Stomach oils, a complex mixture of neutral i1 10 20 30 40 50 60 , are typical of procellariiform (, shearwaters, 0 ). All procellariforms, with the exception of diving AGE (DAYS) petrels, produce stomach oils and feed them to their young. It is known that stomach oils are not secretory products, but are dietary in origin (Cheah and Hansen 1970; Clarke and Prince 1976; Imber 1976) and are formed in the proventriculus by a combination of specialized gastric anatomy and physiology (Roby et al. 1989; Place et al. 1989). The adaptive significance of stomach oils is still a matter of conjecture (Warham 1977; Jacob 1982). The objectives of the study were (a) to determine the relationship between stomach oil ingestion and the growth, development, and energetics of seabird nestlings, (b) to deter- mine the contribution of stomach oils to the overall energetic efficiency of the parent-offspring unit, and (c) to compare, using Figure 1. Growth In body mass of control and crossfostered chicks. Crossfostered prion chicks were raised by radio-labeled markers, the handling of dietary lipids in chicks South Georgia diving foster parents. Error bars indicate ± one that are fed stomach oils with those that are not. standard error of the mean. The subjects of our study were antarctic prions, desolata, a species that feeds its young stomach oils, and South Georgia diving petrels, Pelecanoides georgicus, a species that lacks similable neutral marker), and carbon-14 labeled polyeth- stomach oils. Chicks of the two species were crossfostered soon ylene glycol (nonassimilable aqueous phase marker). Adult free- after hatching, and their growth, development, and rate of lipid ranging metabolic rates during the chick-rearing period were deposition, as well as those of control chicks, were monitored measured using the doubly-labeled water technique. throughout the nestling period. Dilution space of tritiated gly- Analysis of data collected in the field has just begun, and cerol triether (GTE), a nonassimilable lipid phase marker, was collected specimens and samples are not yet analyzed, but some used to estimate stomach oil volume in control and crossfostered preliminary conclusions can be drawn. parents chicks. Chicks of the two species were also brought into the feed their chicks about twice as frequently as prion parents, but laboratory and raised on either high-oil or low-oil diets. Growth average size of diving petrel chick meals was 30 percent less than rates of lab-reared chicks were monitored, and excreta was col- that of prions. Due to the higher feeding frequency, the average lected for analysis of biochemical composition. Patterns of lipid daily mass of food delivered to diving petrel chicks was about deposition in lab-reared chicks, as well as crossfostered and one-third greater than in prion chicks, but diving petrel chick control chicks, were tracked nondestructively by using total meals lacked stomach oils. Field-control prion chicks had on body electrical conductivity body composition analysis. Rela- average 2.0 milliliters (up to 14.1 milliliters) of stomach oils, and tive transit rates and lipid assimilation efficiencies in the two crossfostered diving petrels averaged 0.48 milliliters of stomach species on the two diets were measured by feeding three radio- oils. There were no detectable quantities of stomach oils in either labeled markers: tritiated GTE, carbon-14 labeled triolein (as- control diving petrels or crossfostered prions. South Georgia

1992 REVIEW 147 200 excess lipid. Prion chicks fed a high-oil diet developed at the same rate as prion chicks on a low-lipid diet, but the rate of body- mass increase was significantly higher. This was due partly to the accumulation of stomach oils in the proventriculus and partly to 150 higher rates of fat deposition in adipose tissue, since they ex- control creted only small quantities of lipids. Stomach oils appear to be an essential adaptation for enhancing the energy density of chick meals in those seabird species that feed their chicks infrequently. Cl) In diving petrels, the ability to produce stomach oils and to 100 process high lipid diets has been secondarily lost, presumably as this taxon evolved to fill a near shore, pursuit-diving niche. x—fostered We wish to thank Dr. J. P. Croxall, P. A. Prince, and British Antarctic Survey support staff at both the Bird Island Research Station and the Cambridge headquarters for their assistance in making this research possible. This work was supported br National Science Foundation grant DPP 90-18091. diving petrels References

Cheah, C. C., and I. A. Hansen. 1970. Stomach oil and tissue lipids of the 0 10 20 30 40 50 petrels Puffinuspacificus and Pterodromamacroptera. International Jour- 1:203-208. AGE (DAYS) nal of Biochemistry, Clarke, A., and P. A. Prince. 1976. The origin of stomach oil in marine birds: Analyses of the stomach oil from six species of subantarctic Figure 2. Growth In body mass of control and crossfostered South procellariiform birds. Journal of Experimental Marine Biology and Georgia diving petrel chicks. Crossfostered diving petrel chicks were raised by antarctic prion foster parents. Error bars Indicate ± Ecology, 23:15-30. one standard error of the mean. Imber, M. J. 1976. The origin of petrel stomach oils: A review. Condor, 78:366-69. Jacob, J. 1982. "Stomach Oils." In D. S. Farner, J . R. King, and K. C. diving petrels could not rear prion chicks, presumably because Parkes (Eds.), Avian Biology. New York: Academic Press, 6:325-40. of the lack of stomach oils (figure 1). Diving petrel chicks reared Place, A. R., N. C. Stoyan, R. E. Ricklefs, and R. G. Butler. 1989. Physio- by prion foster parents grew at lower rate and fledged later than logical basis of stomach oil formation in Leachs storm petrel control diving petrel chicks (figure 2). (Oceanodromaleucorhoa). Auk, 106:687-99. Diving petrels fed high-lipid diets in the lab lacked the ability Roby, D. D., K. L. Brink, and A. R. Place. 1989. Relative passage rates of to efficiently digest and to assimilate dietary lipids and also lipid and aqueous digesta in the formation of stomach oils. Auk, 106:303-13. excreted considerable lipid. The development of these chicks, Warham,J. 1977. The incidence, functions and ecological significance measured as the rate of wing-length increase, was retarded, of petrel stomach oils. Proceedings of New Zealand Ecological Society, presumably due to excretion of essential nutrients along with 24:84-93.

South polar skuas at McMurdo marine ecosystem as both a predator and a scavenger. During the breeding season, the skuas come ashore all around the ant- Station, Ross Island, 1991-1992 arctic continent to nest on land. Like gulls, they are opportunistic feeders. As such, they feed on food sources such as refuse from G. D. MILLER, C. E. WALLACE, human settlements or research stations. B. M. KEIMEL, AND P. MARTIN We began observations on the skuas around McMurdo Sta- tion beginning with our arrival on 23 October 1991. From the evening of 10 November 1991 through 14 November 1991, we Biology Department conducted formal twice-daily surveys of all the skuas around University of New Mexico McMurdo Station, Observation Hill, and Cape Armitage. As part Albuquerque, New Mexico 87131 of the U.S. Antarctic Programs effort to improve the environ- mental impact of its bases, the dump at McMurdo was cleaned, capped, and closed in 1991-1992. We repeated the surveys on 22 As part of our study of the south polar skua (Chatharacta December 1991 (dump still available) and on 5 February 1992, maccormicki) around Ross Island during the 1991-92 austral sum- after the dump was completely capped, to track the local skuà mer, we collected data on how skuas used McMurdo Station. We population as the season continued. The sudden loss of this observed the skuas at McMurdo during the early season and at resource in late 1991 may have repercussions in the local and mid- and late-season to determine their reproductive success and nearby skua populations. Given the number of skuas around the what parts of the station attracted them the most. McMurdo dump in the early season each year, the dump prob- The south polar skua is a long-lived seabird that breeds ably was an important food source before Adélie penguins around Antarctica. It is an important component of antarctic (Pygoscelis adeliae) laid their eggs in nearby rookeries and while

148 ANTARCTIC JOURNAL