The dark-morph Herald Petrel Pterodroma heraldica
Résumé
Whether dark-morph Herald Petrel Pterodroma heraldica exists or not
has been debated for many years. We summarise previous contributions on the
subject, provide indisputable evidence of the dark morph, describe its plumage
based on museum specimens and live birds, highlight differences between dark,
light and intermediate morphs, and enumerate characters that relatively easily
separate the dark morph from ‘all-dark’ Henderson Petrel P. atrata. Dark-morph
Herald Petrel is scarce and local. Since the 1970s, records have been restricted
to the central South Pacific at Mangareva Island (Gambier Islands) and Ua Pou
(Marquesas Islands).