Of the two species of Giant-Petrel, only the Southern is known to occur in a white morph. These white birds, sometimes called "Nelly" comprise less than 10% of the population with the vast majority on the Antarctic mainland. Thus we were surprised to find this apparent adult in South Georgia. White morph birds are described as sparsely flecked with black on the body and wings, and with dark brown eyes. Our bird is unusual in having pale eyes. Canon PowerShot SX50 HS.
References:
Brown RM, Techow NMSM, Wood AG, Phillips RA (2015) Hybridization and Back-Crossing in Giant Petrels (Macronectes giganteus and M. halli) at Bird Island, South Georgia, and a Summary of Hybridization in Seabirds. PLoS ONE 10(3): e0121688. https://doi.org/10.1371/journal.pone.0121688
Marchant, S. & Higgins, P.J. (coordinating editors) 1990. Handbook of Australian, New Zealand & Antarctic Birds. Volume 1, Ratites to ducks; Part A, Ratites to petrels. Melbourne, Oxford University Press .
Szabo, M.J. 2013. Southern giant petrel. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz