. The Canadian field-naturalist. 114 The Canadian Field-Naturalist Vol. 100 Using Eggshells to Determine the Year of a Common Loon. Gavia immer, Nesting Attempt Robert Alvo and Kent Prior Biology Department, Trent University, Peterborough, Ontario K9J 7B8 Alvo, Robert, and Kent Prior. 1986. Using eggshells to determine the year of a Common Loon, Gavia immer, nesting attempt. Canadian Field-Naturalist 100(1): 114-115. A simple method is described for determining whether a Common Loon (Gavia immer) nesting attempt occurred in the current year or in a previous year, based on the extent of fading
. The Canadian field-naturalist. 114 The Canadian Field-Naturalist Vol. 100 Using Eggshells to Determine the Year of a Common Loon. Gavia immer, Nesting Attempt Robert Alvo and Kent Prior Biology Department, Trent University, Peterborough, Ontario K9J 7B8 Alvo, Robert, and Kent Prior. 1986. Using eggshells to determine the year of a Common Loon, Gavia immer, nesting attempt. Canadian Field-Naturalist 100(1): 114-115. A simple method is described for determining whether a Common Loon (Gavia immer) nesting attempt occurred in the current year or in a previous year, based on the extent of fading of the outer shell surfaces. Key Words: Eggshell, fading, nesting attempt. Common Loon, Gavia immer. One of the major problems with conducting a sur- vey of breeding Common Loons (Gavia immer) is the large area that must be surveyed to obtain a sufficient sample size. The number of visits to a particular nest is therefore often limited (Vermeer 1973; Mclntyre 1975), and it is common to find nests only after the eggs have hatched or have been preyed upon. Since loon chicks are precocial, the eggshells are usually left on the nest by the parents (Olson and Marshall 1952), often remaining there for one or two years (personal observation). When a nest for which no previous records are available is found with eggshells, but without any yolk, albumen or egg membrane, it is sometimes possible to distinguish between a nesting attempt that occurred during the current year and one of a previous year. For example, old shells are often found buried under nest material; also, old nests are often disheveled and may have fresh growing vegeta- tion. However, nests found during the year of the nesting attempt sometimes also show these character- istics. We report here a method for examining the extent of fading of the eggshells, which can be used to determine whether or not the nesting attempt occurred during the current year. During a survey of breeding Common Loons in the Sudbury, Ontario, ar
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