GEOGRAPHIC VARIATION AND REASSESSMENT OF SPECIES LIMITS IN THE 'MASKED' BOOBIES OF THE EASTERN PACIFIC OCEAN

摘要

Two distinct forms of Masked Boby (Sula dactylatra) occur in the eastern Pacific: (1) a yellow-billed form that includes a population on Clipperton Island and islands off western Mexico (S. D. "cal- ifornica"), and another, unnamed, population on Las Islas Desventuradas, Chile, and (2) an orange-billed form [S. (d) granti] that nests almost exclusively on the islands of the Galapagos and on Malpelo Island, Colombia. Quantitative comparisons, including discriminant function analysis (DFA) of standard morphological characters Indicated that yellow-billed populations are only marginally different from one another, and neither is consistently Separable from S. d. personata, a yellow-billed form that ranges over most of the tropical Pacific.