Refined Colorimetry Validates Endangered Subspecies of the Least Tern

In contrast to the results of Thompson et al. (1992), refined colorimetry validates three subspecies of Least Tern in North America, Sterna antillarum antillarum (Lesson), S. a. browni Mearns, and S. a. athalassos Burleigh and Lowery. Four of nine color characters exhibited significant seasonal differences, presumably a result of plumage wear and bleaching. The sexes differed in lightness and hue of dorsum and hind neck. Males of S. a. athalassos differed significantly from those of both S. a. antillarum and S. a. browni in lightness of dorsum, and males of S. a. browni differed significantly from those of S. a. antillarum in lightness of hind neck. Females generally showed patterns concordant with males. Because S. a. browni and S. a. athalassos are listed as endangered, the validity of these taxa is important to conservationists and managers. Rigorous systematic methodology and scientific collections of high quality are indispensable to conservation biology.