Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch 7700, South Africa Published values for the utilization efficiency of seabirds have come entirely from work on chicks and juveniles fed exclusively on fish (Dunn 1975; Cooper 1977, 1978, 1980). Squid is an important component of the diet of many species, however, comprising up to 90% of prey taken by King Penguins (Aptenodytes patagonicus; Stonehouse 1960, Croxall and Prince 1980, Croxall 1984). Because the utilization efficiency of birds is known to vary depending on the food con- sumed (Uramoto 1961), the applicability of the pub- lished data to such species is uncertain. This study presents the first measurements of the assimilation efficiency of a predominately squid-eating adult sea- bird fed on squid. The study was conducted at sub-Antarctic Marion Island (46ø54'S, 37ø55'E) during September 1981 and April 1982. Four nonbreeding adult King Penguins were housed indoors, individually confined to small cages, and fasted for 48 h before commencement of the experiment. Room temperature varied between 5øC and 15øC, within the thermoneutral zone of King Penguins (Groscolas et al. 1981). The penguins were then fed for 5 days on a diet consisting exclusively of the South Atlantic cool-water squid Loligo reynaudi. Each bird was weighed daily before being fed a known mass of food sufficient for it to maintain con- stant mass over the period of the experiment. A pre- weighed plastic sheet underneath a wire mesh floor allowed for the daily collection of excretory prod- ucts, which were then dried to constant mass at 60øC. Homogenized portions of oven-dried squid and ex- cretory products were analyzed individually for en- ergy content with a Phillips micro-bomb calorimeter. Utilization efficiency was calculated as gross energy intake minus excretory energy expressed as a per- centage of gross energy intake. Gross energy intake, excretory energy, and utili- zation efficiency were calculated per bird over the 5 days and the averaged results for the four birds are given in Table 1. The wet mass of food consumed daily averaged 6.1% of total body mass. The daily squid intake of 699 g/d was close to the 675 g/d of fish fed to King Penguins maintained at the Montreal Aquarium (Penfold 1979). The energy value of squid was 22.1 + 0.5 kJ/g dry mass (n = 8; 5.23 kJ/g wet mass), a value 14% higher than that obtained by Coo- per (1979) for the same species. Excretory output was similar to that measured by Burger et al. (1978), av- eraging 8.4% higher. The energy value of excretory products was 13.2 + 0.7 kJ/g dry mass (n = 23), a value 8.3% lower than that obtained by Burger et al. (1978). The mean efficiency of utilization of four birds was 81.3%. The calculated utilization efficiency of captive adult King Penguins fed squid is near the upper limits of the range observed for young piscivorous seabirds fed on fish (Table 2). Estimates of food consumption by squid-eating species based on these data (e.g. Prince et al. 1981, Croxall and Prince 1982a) will therefore be substantially correct. This confirmation has considerable ecological significance for bioener- getics modelling (see Croxall and Prince 1982a), be- cause King Penguins and other squid-eating species comprise a large proportion of the total seabird bio- mass in the sub-Antarctic region. Published values for the energy content of squid, mainly from the northern hemisphere, are appreci- ably lower than those for the energy content of Ant- arctic krill and fish (Croxall and Prince 1982b). The energy value of squid meals fed to Black-browed (Di- omedea melanophris) and Grey-headed albatross (D. chrysostoma) chicks at South Georgia, however, fall within the range measured for Antarctic fish (Clarke and Prince 1980) and krill (Euphausia superba; Clarke TABLE 1. Gross energy intake, excretory energy, and utilization efficiency of King Penguins. Utilization Bird mass Energy input Energy excreted efficiency (kg) (kJ / a) (kJ / a) (%) Mean 11.53 3,605.6 677.3 81.3 Range 11.3-11.75 4,495.0-2,955.3 469.2-873.6 79.8-84.3 TA3LE 2. Efficiency of utilization of squid and fish by seabirds. Utili- zation effi- ciency Species Age class n Diet (%) References Great White Pelican Juvenile 1 Fish 73.0 Cooper 1980 ( Pelecanus onocrotalus) Cape Gannee Chick 2 Fish 74.2 Cooper 1978 (Sula capensis) Jackass Penguin a Chick 2 Fish 75.3 Cooper 1977 ( Spheniscus demersus) Cape Gannet Juvenile 2 Fish 76.1 Cooper 1978 (Sula capensis) Adlie Penguin Chick ? ? 80.0 D.P. Da Costa in (Pygoscelis adeliae) Kooyman et al. 1983 King Penguin Adult 4 Squid 81.3 This study (Aptenodytes patagonicus) Double-crested Cormorant' Chick >6 Fish 85.0 Dunn 1975 (Phalacrocorax auritus) Utilization-efficiency values are averages over the growth period. 1980). These data re-emphasize the need for compo- sitional analyses of individual prey items available to Antarctic and sub-Antarctic predators and for fur- ther investigation into whether or not variation in energy content of prey may be reflected in avian uti- lization efficiencies. Scientific research at Marion Island was carried out under the auspices of the South African Scientific Committee for Antarctic Research. Financial and lo- gistical support was provided by the South African Department of Transport. P. Van Litsenborgh pro- vided help in handling the birds. LITERATURE CITED BURGER, A. E., H. E. LINDEBOOM, &: A. J. WILLIAMS. 1978. The mineral and energy contributions of selected species of birds to the Marion Island terrestrial ecosystem. South African J. Antarctic Res. 8: 58-70. CLARKE, A. 1980. The biochemical composition of krill (Euphausia superba) from South Georgia. J. Exp. Mar. Biol. Ecol. 43: 221-236. --, & P. A. PRINCE. 1980. Chemical composition and calorific value of food fed to mollymauk chicks Diomedea melanophris and D. chrysostoma on Bird Island, South Georgia. Ibis 122: 488-494. COOPER, J. 1977. Energetic requirements for growth of the Jackass Penguin. Zool. Africana 12: 201- 213. 1978. Energetic requirements for growth and maintenance of the Cape Gannet (Aves: Sulidae). Zool. Africana 13: 305-317. . 1979. Length-mass relationships, water con- tent and energy values for two species of squid, Loligo reynaudi and Todaropsis eblanae, off the South-Western Cape. Fish. Bull. South Africa 11: 43-45. 1980. Energetic requirements for mainte- nance of a captive juvenile Great White Pelican Pelecanus onocrotalus. Cormorant 8: 17-19. CROXALL, J.P. 1984. Seabird ecology. Pp. 533-616 in Antarctic ecology (R. M. Laws, Ed.). London, Academic Press. --, & P. A. PRINCE. 1980. Food, feeding ecology and ecological segregation of seabirds at South Georgia. Biol. J. Linnean Soc. 14: 103-131. --, & . 1982a. A preliminary assessment of the impact of seabirds on marine resources at South Georgia. Pp. 501-509 in CNFRA Colloque sur les ecosystems subantarctiques, 51 (P. Jou- ventin, L. Massa, and P. Trehen, Eds.). --, & . 1982b. Calorific content of squid (Mollusca: Cephalopoda). Brit. Antarctic Surv. Bull. 55: 27-31. DUNN, E.H. 1975. Caloric intake of nesting Double- crested Cormorants. Auk 92: 553-565. GROSCOLAS, R., Y. LE MAHO, H. BARRE, & B. DESPIN. 1981. Strategie d'adaptation au froid chez le Manchot royal (subantarctique): comparaison avec le Manchot empereur (antarctique). Pp. 339- 344 in CNFRA Colloque sur les ecosystems sub- antarctiques, 51 (P. Jouventin, L. Masse, and P. Trehen, Eds.). KOOYMAN, G. L., R. W. DAVIS, J. P. CROXALL,  D. P. COSTA. 1983. Diving depths and energy re- quirements of King Penguins. Science 217: 727. PENFOLD, V. 1979. Exhibition of penguins in the Montreal Aquarium. Intern. Zoo Yearbook 18: 70-72. PRINCE, P. A., C. RICKETTS, & G. THOMAS. 1981. Weight loss in incubating albatrosses and its im- plications for their energy and food require- ments. Condor 83: 238-242. STONEHOUSE, B. 1960. The King Penguin (Aptenody- tes patagonicus). 1. Breeding behaviour and de- velopment. Falkland Islands Dependencies Surv. Sci. Repts. No. 23. URAMOTO, M. 1961. Ecological study of the bird community of the broad-leaved deciduous forest of central Japan. Misc. Repts. Yamashina Inst. Ornithol. Zool. 3: 1-32. Received 11 October 1983, accepted 26 March 1984.