BEHAVIORAL AND MOLECULAR EVIDENCE FOR SPECIFIC STATUS OF LIGHT AND DARK MORPHS OF THE HERALD PETREL PTERODROMA-HERALDICA

The Herald Petrel Pterodroma heraldica has an extensive subtropical br eeding range across the width of the Pacific Ocean. It occurs in dark and light morphs, and, at most breeding colonies, the latter is more n umerous. However, on Henderson Island, one of the Pitcairn Islands of the Central Pacific, the dark morph is more numerous. During a field s tudy at Henderson Island, we found evidence of reproductive isolation between light and dark Herald Petrels. The morphs bred and courted ass ortatively, They also tended to breed in different parts of the island (dark birds nearer the coast) and at slightly different seasons (dark birds mostly in the austral winter, light birds more evenly throughou t the year) and uttered different calls, Together, these data strongly suggested that the morphs are distinct species. This conclusion was s upported by sequence data from a 307-base pair region of the cytochrom e b gene of the mitochondrial genome, When birds of both morphs from H enderson and light morphs from Ducie Atoll (345 km west of Henderson) were sampled, five haplotypes were restricted to light Herald Petrels; they did not occur in dark birds, In contrast, three haplotypes were restricted to dark Herald Petrels on Henderson Island. Thus, the haplo types of the two morphs were mutually exclusive, further indicating re productive isolation between them. We propose that the white-bellied f orm should retain the name Herald Petrel P. heraldica, while the dark- bellied form should be granted specific status as the Henderson Petrel Pterodroma atrata (Mathews 1912). The name atrata derives from a desc ription written by Solander on Cook's first voyage, Molecular data fro m Round Island Petrels Pterodroma arminjoniana confirmed the close rel ationship between this form and heraldica. However, arminjoniana and a trata did not share sequences for the cytochrome b region studied.