. The Canadian field-naturalist. Natural history. 352 The Canadian Field-Naturalist Vol. 84 lows: empty-eggshell weight including mem- branes, egg length (L), egg breadth (B) at its widest portion, L/B ratio, estimated outside volume and eggshell thickness including mem- branes and cuticle. Tyler (1969) has described in detail the shell structure of Gaviiformes and it is obvious that our measurements of thickness encompassed many various structures. Amadon (1943/)) described various methods used to obtain measurements relating to egg volume. We estimated volume on the basis of the shape catego
. The Canadian field-naturalist. Natural history. 352 The Canadian Field-Naturalist Vol. 84 lows: empty-eggshell weight including mem- branes, egg length (L), egg breadth (B) at its widest portion, L/B ratio, estimated outside volume and eggshell thickness including mem- branes and cuticle. Tyler (1969) has described in detail the shell structure of Gaviiformes and it is obvious that our measurements of thickness encompassed many various structures. Amadon (1943/)) described various methods used to obtain measurements relating to egg volume. We estimated volume on the basis of the shape categories described by Preston (1953) and Palmer (1962: 13) and the constant LB' as discussed by Amadon (1943ft). Examples (10 to 11 each) of the two shape categories we found in loons, subelliptical and oval, were im- mersed in water for a volumetric determination of outside volume. Cylinder volumes with equi- valent L and B measurements of each egg were calculated and a correction factor (CF) for each shape determined. We originally planned to calculate a CF-regression formula for differ- ing L/B ratios within each shape category, but found them to be remarkably agreeable within the ranges we tested, and therefore combined them. The resultant CF's were as follows: subelliptical = , oval = We multi- plied these by the volume of a cylinder of equal L and B for each egg to obtain our esti- mate of volume. This procedure is essentially similiar to that described by Stonehouse (1963). The hypothesis which we tested is re- stated as follows; (1) geographic variation in eggshells occurs in North American Common Loons, and (2) it occurs according to the trends (wing chord as an index to body size) described by Rand (1947). Statistical tests were (1) analysis of variance, and (2) Dunc- an's new multiple-range test (Steel and Torrie 1960: 112-15, 107-09). The hypothesized trends are summarized in Fig. 1 as we vision them from Rand's descriptions. Results and Discussion Eggshell Me
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