168 ShortCommunications [Auk, Vol. 99 the faunal remains suggest late winter to summer that the Great Auk "may have strayed to the coast occupation of the site (Cox and Spiess 1980). of Labrador," but he showed that there was no sat- The remainsof Great Auk from Avayalik-1 consist isfactory evidence of such an instance. The speci- solely of a completeright coracoid,a portion of the mens from Avayalik Island thus constitutethe sole proximal end of a left coracoid, and a complete left record of Pinguinusimpennis from Labrador. femur. The coracoids are from birds of noticeably We are grateful to Ralph S. Palmer and Douglas different size, so at least two individuals are repre- Sutton for information and comments on the manu- sented. The rarity of the Great Auk in these deposits script. indicates the likelihood that the few birds taken were in passageand that the speciesdid not breed in the LITERATURE CITED area. BRODKORB,P. 1967. Catalogue of fossil birds: Part Not only were Great Auks used for food by Eski- 3 (Ralliformes, Ichthyornithiformes, Charadri- mos and Indians, as demonstratedby bonesin mid- iformes). Bull. Florida State Mus., Biol. Sci. 11: dens from Greenland to Florida (Greenway 1958, 99-220. Brodkorb 1967), but in some cultures the bird evi- Cox, S. L., & A. SPIESS.1980. Dorset settlement and dently had ceremonial significanceas well. This is subsistence in northern Labrador. Arctic 33: best exemplified by a burial in a Maritime Archaic 659-669. cemetery, Port au Choix-3, in northwestern New- GREENWAY,J. C. 1958. Extinct and vanishing birds foundland, dating to 2300-1800 B.C. A single human of the world. New York, American Committee skeleton found here had over 200 beaks of the Great for International Wild Life Protection. Auk distributed over its length, the body having ap- JORDAN,R. H. 1979-80. Dorset art from Labrador. parently been clothed in a garment consistingen- Folk 21-22: 397-417. tirely of Great Auk skins (Tuck 1976). The fact that --. 1980. Preliminary resultsfrom archaeologi- the bonesobtained from Avayalik Island comefrom cal investigations on Avayalik Island, extreme deep within the body (coracoids and femur), and northern Labrador. Arctic 33: 607627. thus would not have been included with a skin, TODD, W. E. C. 1963. Birds of the Labrador Penin- practicallyprecludes the specimenshaving been ob- sula and adjacent areas. Toronto, Univ. Toronto tained through trade with contemporaneouscultures Press. to the south. TucK, J. A. 1976. Ancient peoples of Port au Choix. The only certainly known breeding site of the Newfoundland Social and Economic Studies, 17. Great Auk in the Western Atlantic in historic times St. John's, Institute of Social and Economic Re- is Funk Island, Newfoundland. Although the species search, Memorial Univ. Newfoundland. is known from midden deposits and a skin from westernGreenland, there is apparentlyno conclusive evidence that it ever bred there (Greenway 1958). Received4 May 1981, accepted18 August1981. Todd (1963: 403) consideredthat it was not unlikely

A Hybrid between the Hooded and Silver Grebes (Podicepsgallardoi and P. occipitalis)

ROBERT W. STORER Museumof Zoology,The Universityof Michigan,Ann Arbor, Michigan48109 USA

Hybrids between speciesof grebes are rare. Voous Grebe (Podicepsauritus) and an Eared Grebe (P. ni- and Payne (1965, Ardea 53: 9) reportedextensive hy- gricollis) reported by Dennis et al. (1973, Scottish bridization between the Madagascar endemic, Birds 7: 307). In this case, an adult of each species Tachybaptusrufolavatus, and the Little Grebe, T. ruf- was observedfeeding and carrying a single young. icollis, which is common on the mainland of Africa While studying the recently described Hooded and probably representsthe stockfrom which T. ru- Grebe (Podicepsgallardoi) (Rumboll 1974, Com. Mus. folavatuswas derived after an earlier invasion. In this Argent. Cienc. Nat. 4: 33), James D. Hammond, instance, the endemic form evidently had not Miguel Hinrichsen, Maurice A. E. Rumboll, and I evolved isolating mechanisms that would have pre- were surprised to observe an apparent hybrid be- vented hybridization with the reinvading ruficollis. tween that speciesand the Silver Grebe (P. occipi- The only other instanceI know of is the likely, but talis). For several days we were aware of a rather unproved, case of hybridization between a Horned pale-headed grebe swimming about in close com- January1982] ShortCommunications 169

T^BLE1. Weightsand measurementsof femalesof Podicepso. occipitalisand P. gallardoiand their hybrid.

P.o. occipitalis Parameter Extremes Mean n Hybrid P. gallardoi Weight 278-410g 334g 4 505g 530;610 g Wing 116-130 mm 125 mm 19 140 mm 148; 157 mm Tarsus 38.0-43.0 mm 39.8 mm 17 46.5 mm 46.6; 47.1 mm Bill from nostril 10.1-13.0 mm 11.6 mm 18 13.1 mm 12.3; 13.4 mm Bill depth 5.3-6.9 mm 5.9 mm 13 6.8 mm 7.5; 7.7 mm

pany with a Hooded Grebe, to which it appeared to hybrid. There is no trace of the postocularwattle be mated. Rumboll collectedit on 8 January1976, found in P. gallardoi.The color of the upper parts is and it was prepared as a partial skin and partial skel- dark gray, as in P. occipitalis.The amount of white eton, with the completeskull and the bones of one on the wing is intermediate; the six outer primaries wing and one leg retained in the skin (Univ. Mich. are dark, and the white of the inner primaries is Mus. Zool. 220,944). It was a female; the ovary con- confined almost entirely to the inner web of the tained two small corpora lutea and many small fol- feathers. The alula and greater coverts of the outer licles approximately 2 mm in diameter. No grebe primaries are almost entirely dark. nests were seen in the course of our visit, and it is How the mating that produced this hybrid came assumedthat the hybrid and its apparent mate had about is unknown. Because P. occipitalisis widely made an unsuccessfulattempt at nesting. The hybrid distributed both to the north and south of the range weighed 505 g and had moderate fat under the feath- of P. gallardoi, it is likely that the parental species er tracts. The pectoralmuscles on one side weighed have been in contact for a long time, long enough 18 grams. The stomach contents were largely snail for both morphologicalchanges and differencesin the tissue and shells, with a few dytiscid adults and lar- pair-formation ceremonies to have evolved through vae, a few chironomid (Psectrocladius)pupae, and selectionagainst hybridization in the sympatricpopu- many small feathers. There was no pyloric plug of lations. In view of the difference in the head patterns, feathers, however, as is found in many species of Advertisingcalls, and in the DiscoveryCeremony, in grebes (e.g. Storer 1969, Condor 71: 185; 1976, Trans. particular the unique Sky-jabbing display of the San Diego Soc. Nat. Hist. 18: 117). No bursa was Hooded Grebe (Storer, in press,Living Bird), I think present, indicating that the bird was at least2 yr old. it unlikely that a long pair bond between birds of In size, the hybrid is intermediate between the these quite different specieswas involved. On the parental species, although closer to or within the other hand, Hooded Grebes are, in my experience, range of the larger P. gallardoiin most measurements much less aggressive than other grebes. I once (Table 1). As in P. occipitalis,the forehead and lores watched a lone Hooded Grebe resting on a platform are gray and the nape black. The anterior part of the of Myriophylluma few centimetersaway from a mat- crown is whitish, blending with pale straw-colored ing pair. Under somewhat similar circumstances, it plumes (slightly tinged with rufous) posteriorly. might be possible for a Silver Grebe to sneak a cop- These plumes resemblethose of P. gallardoiin po- ulation with a Hooded Grebe whose mate was not sition but are shorter and much paler. They mingle at hand. with the black of the posterior part of the crown in I am grateful to my coworkers,J. D. Hammond, contrast with the sharp demarcation of the colors in M. Hinrichsen, and M. A. E. Rumboll, who made the parental species. The chin and throat are gray the fieldwork possible, and to the National Geo- (mixed with white posteriorly), intermediate be- graphic Society, which provided the necessaryfund- tween the light brownish gray of P.o. occipitalisand ing. the velvet black of P. gallardoi.Posterior to the eyes there are elongatedplumes like those of P.o. occip- Received23 February1981, accepted30 June1981. italis, but these are fewer, paler, and shorter in the