--The literature contains few records of eggs found to be cracked while incubation is in progress. Cracking may be a more common phenomenon than is generally recognized. Freezing tem- peratures and especially competition for nest sites among cavity nesting species are among the causes. It has been generally assumed that cracked eggs of wild birds do not hatch. Greenwood (1969) reported frost cracking of Mallard (Anas platyrhynchos) eggs in the central Missouri Coteau of eastern North Dakota. He noted five nests each with one or more cracked eggs. One of these cracked eggs hatched. Allen Brooks (in Bent 1925), described Bufflehead (Bucephala albeola) nests and eggs and stated that, "In many cases the eggs had fine cracks, evidently made by the compression of the bird's body when entering the small aperture." Philips (1925) reports cracked eggs in Bufflehead and Barrow's Goldeneye (B. islandica) nests. Erskine (1960) found a cracked and dried out Bufflehead's egg among the residue of a hatched clutch of mixed Barrow's Goldeneye and Bufflehead eggs. The cause of cracked eggs Greenwood (1969) reported was frost, but among cavity nesting ducks competition for nest sites may be a factor. Severe fighting may even lead to the death of some females. Erskine (1959, 1960) and McLaren (1969) recorded dead female Buffleheads in Barrow's Goldeneye nests. Grenquist (1963) reported fights between egg-laying female Common Goldeneyes (B. clangula) and even one or two dead females in the same nest box. Clutches of Common Goldeneyes and Hooded Mergansers (Lophodytes cucullatus) were examined in a study of cavity nesting ducks of Elk and Long Lakes, On- tario. Hooded Merganser eggs have remarkably thick and tough shells and none with cracks were found, but cracked and broken Common Goldeneye eggs were found in two nests and broken or preyed on eggs in another two. A single Golden- eye egg disappeared from a mixed Goldeneye-Hooded Merganser clutch. Two clutches of Common Goldeneye's eggs were collected and shipped for in- cubator hatching to the Guelph station of the Ontario Waterfowl Research Foun- dation. The first clutch, of 11 eggs, was taken from a box on Elk Lake at 0530 and was under incubation at Guelph by 1230 on 5 June 1974. One of these eggs was cracked, but the entire dutch hatched on 7 June. The second clutch, of 8 eggs, was collected from a box on Long Lake at 0430 on 25 June 1974 and placed in the incubator by 1330. Five of these eggs were found to be cracked; indeed, the shells of two were so badly damaged that shell chips were missing. The under- lying portion of membrane, over 25 mm long in both cases was visible, intact, and discolored dark gray. Because no odor of decomposition was detectable in these eggs, they were put in the incubator, and all of them hatched during the night of 1-2 July. The incubation period for Common Goldeneyes reported in the literature is variable and sometimes misleading. Bent (1925) and Kortright (1943) report 20 days, Phillips (1925) 24-28 days Delacour (1959) 26 days Laidlay (1933) 26 days Dement'ev et al. (1967) 30 days. At the Ontario Waterfowl Research Foun- dation facilities five clutches of Common Goldeneye eggs have been hatched in an incubator for which the incubation period is known accurately. These periods were 28, 2% 30, 30, and 30 days. This is within the limits of 28 to 34 days recorded by Erskine (1972) for the incubation periods of the tribe Merglnl. He also esti- mated an egg deposition rate of 1.5 days per egg for these ducks. Using these time brackets, the Elk Lake clutch No. 1 can be backdated from hatch to about 8 May for the beginning of incubation and to about 23 April for the first egg date. Weather records are available at Elk Lake from 6 May 1974 when the Ontario Ministry of Natural Resources office started operating its weather station. Minimum night temperatures from 6 to 8 May were -0.6 -11.1, and -2.2øC respectively. The Atmospheric Environment Service station at Kirkland Lake, 51 km northeast of Elk Lake recorded minimum temperatures of -2.8, -6.7 -1.7, -6.1, 0.6, 2.8, 0.6, -1.7 -6.7, -5.6 -3.3, -5.0, -8.3, -2.2, -3.9, and 0øC respectively for the period 23 April to 8 May. These temperatures appear to be low enough to crack eggs, particularly in the absence of insulating nest material. The Common Goldeneyes in the Elk Lake area gradually accumulate a layer of down in their nests as laying proceeds. Generally the box does not contain enough material to provide adequate insulating cover for the eggs until the clutch is nearly complete. The Long Lake clutch was first found with five eggs on 27 May. Laying probably started about 18 or 19 May and incubation from about 1 June. Minimum tempera- tures for this period at Elk Lake varied between -1.1 ø and 10.0øC; 19 May was the only night with a below freezing temperature. Freezing could not have been a factor in cracking 5 of this clutch of 8 eggs. Fighting among females was probably responsible for it, although no strife was seen. We are grateful to G. Bain and J. Knowles who assisted in most aspects of the cavity nesting duck study. This paper is contribution No. 75-2 Fish & Wildlife Research Branch, On- tario Ministry of Natural Resources, Maple, Ontario. BENT, A. C. Bull. 130. DELACOUR, J. Ltd. LITERATURE CITED 1925. Life histories of North American wild fowl. U.S. Natl. Mus. 1959. The waterfowl of the world, vol. 3. London, Country Life DEENT'EV, G. P., N. A. GLADKO% YU. A. ISAKOV, N. N. KARTASi:{EV, S. V. KmIKOV, A. V. MIKHEEV, AND E. S. PTUSrENKO. 1967. Birds of the Soviet Union 4: 1-683. (Jerusalem, Israel Program for Sci. Transl.) ERSKXE, A. J. 1959. A joint clutch of Barrow's Goldeneye and Bufflehead eggs. Canadian Field-Naturalist 73: 131. ERSKNE, A. J. 1960. Further notes on interspecific competition among hole- nesting ducks. Canadian Field-Naturalist 74: 161-162. ERSKmE, A. J. 1972. Buffleheads. Canadian Wildl. Serv. Monogr. Ser. 4: 240. GmENWOOD, R. J. 1969. Mallard hatching from an egg cracked by freezing. Auk 86: 752-754. GRENQUIST, P. 1963. Hatching losses of Common Goldeneyes in the Finnish Archipelago. Proc. 13th Intern. Ornithol. Congr.: 685-689. KORTmGrT, F. H. 1943. The ducks, geese and swans of North America. Washing- ton, D.C., Amer. Wildl. Inst. LAInLAY, J. C. 1933. The care and propagation of ornamental waterfowl. Edin- burgh, McLagan and Cumming. McL^E, W.D. 1969. Further data on interspecific competition at a joint Buffle- head Goldeneye nest site. Canadian Field-Naturalist 83: 59-61. PLLPS, J. C. 1925. A natural history of the ducks, vol. 3. Boston, Houghton Mifflin Co. H^PY G. L*JXSDEN, Fish and Wildlife Research Branch, Ontario Ministry of Natural Resources, Maple, Ontario LOJ lEO, Canada, and ROBERT WEnTING, Ontario Waterfowl Research Foundation, 387 Kortright Road, Guelph, Ontario, Canada. Accepted 29 Apr. 75.