. The Canadian field-naturalist. 294 The Canadian Field-Naturalist Vol. 114. Figure 1. Ratio of estimated to actual production (C) as determined by tiie detection rate (R) of uniiatciied eggs and the iiatciiing success (S) of eggs in suc- cessful nests. eggshells are approximately times as thick as those of Common Goldeneyes and twice as thick as those of Wood Ducks (Dugger et al. 1994; SouUiere 1987; Zicus et al. 1988), so it was not surprising that a higher proportion of their eggs survived over win- ter than did those of the other two species. In con- trast, Common Goldeneye eggshells,
. The Canadian field-naturalist. 294 The Canadian Field-Naturalist Vol. 114. Figure 1. Ratio of estimated to actual production (C) as determined by tiie detection rate (R) of uniiatciied eggs and the iiatciiing success (S) of eggs in suc- cessful nests. eggshells are approximately times as thick as those of Common Goldeneyes and twice as thick as those of Wood Ducks (Dugger et al. 1994; SouUiere 1987; Zicus et al. 1988), so it was not surprising that a higher proportion of their eggs survived over win- ter than did those of the other two species. In con- trast, Common Goldeneye eggshells, although thin- ner than Hooded Merganser's, are 35-40% thicker than Wood Duck eggshells. Thus, one might not expect Common Goldeneye eggs to be the most frag- ile. Zicus et al. (1988) measured goldeneye eggshells that were 15% thinner than museum eggs collected about 1900 and determined that 21% of the shell weight variation, controlled for egg size, was explained by DDE concentrations. Furthermore, of the Common Goldeneye eggs they observed in successful nests cracked or broke during incuba- tion compared to only 1% of the Wood Duck or Hooded Merganser eggs. Perhaps shell thinning has weakened Common Goldeneye eggshells and con- tributed to their high rate of over-winter breakage. I did not test for species differences in rates of egg disappearance because relatively few eggs disap- peared completely. Wood Ducks have the smallest eggs of the three species studied (Bellrose and Holm 1994; Dugger et al. 1994; Eadie et al. 1995), and the data suggested that their eggs might have disap- peared at the highest rate. Common Goldeneye eggs, although being the largest of the three species, seemed to disappear at a rate nearly equal to Wood Ducks. Perhaps, disappearance of goldeneye eggs might have been facilitated by their greater tendency to break. Hooded Merganser eggs seemed least like- ly to disappear over winter. Broken eggs that had not been removed sometimes were so severel
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