Sex and Age Determination in the American Coot

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).