Sex and Age Determination in the American Coot

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Abstract
The lack of dimorphic plumage makes sex and age detn. difficult. Studies of captive coots (Fulica americana) showed that the bursa of Fabricius is not reliable as a method of age detn., but that leg color is; i.e., gray-green for immatures, yellow-green for yearlings and yellow for 2 yr.-olds and older. Voice dimorphism was reliable in sexing coots in the field. However, certain displays are also distinctive by sex. Coots with a mid-toe-metatarsus measurement of 128 mm. or over are males 85% of the time; those under 128 mm. are females 87% of the time. Less satisfactory sex and age criteria also are discussed. Based upon the better methods, ratios in 123 central Calif. coots were 108 males: 100 females and (corrected) 100 immatures: 24 yearlings: 1.6 adults (territorialism probably caused the adult figure to vary from the expected figure of 10 or 12).

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