. The Canadian field-naturalist. Natural history. 354 The Canadian Field-Naturalist Vol. 84 â Clutch-sizes of Common Loons from various geographical areas Geographical Sample Mean 95% confi- Area' size clutch-size dence limits 1-1-2 23 3 4-4 65 5 58 6 20 7 17 0. 00 all 183 'See Table 2, footnote 1. -All clutches we found in museums were composed of two eggs, therefore the zero values for 95% Confidence Limits. Most of these eggs were collected by one coll- ector, and might be biased away from single eggs. Since areas 5 and 6 tended to hav
. The Canadian field-naturalist. Natural history. 354 The Canadian Field-Naturalist Vol. 84 â Clutch-sizes of Common Loons from various geographical areas Geographical Sample Mean 95% confi- Area' size clutch-size dence limits 1-1-2 23 3 4-4 65 5 58 6 20 7 17 0. 00 all 183 'See Table 2, footnote 1. -All clutches we found in museums were composed of two eggs, therefore the zero values for 95% Confidence Limits. Most of these eggs were collected by one coll- ector, and might be biased away from single eggs. Since areas 5 and 6 tended to have the higher L/B (Table 2; admittedly, there is a great deal of overlap, and differences are only slight), our tentative conclusion is that different tendencies in L/B ratios must at least in part be related to different shape tendencies. The loon eggs with the greatest L/B ratios were the eggs which tended more toward subelliptical and those with the smallest L/B ratios tended more toward oval. Clutch-size Much discussion has been presented regard- ing geographical variation in clutch-size (see Lack 1954, 1968; Cody 1966; and others). There seemed to be little difference between the mean clutch-size between most areas, except in our samples from area 5, where differences seemed apparent (P < differences from all but 1 and 2). There appears to be a rough trend for clutch-size to increase out from this area (Table 3). When areas 1 and 2, and 3 and 4 were analysized singly, no differences or even trends could be found, thus their combin- ations in Table 3. Unfortunately, we had no data from Greenland, Baffin Island, or North- west Territories to test for further changes in the trend. Mean egg volume showed no rela- tionship to clutch-size due to the variability in clutch-size. We do not know, however, if the clutch-size data were biased by failure to collect one-egg clutches in some areas. Such clutches are reportedly fairly common for G. immer (see Olson and Marshall 19
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