The Gibson Plumage Index (GPI), sometimes known as the Gibson Code, is a system for describing the

plumage Plumage ( "feather") is a layer of feathers that covers a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage differ between species and subspecies and may vary with age classes. Within species, ...

great albatross The great albatrosses are seabirds in the genus ''Diomedea'' in the albatross family. The genus ''Diomedea'' formerly included all albatrosses except the sooty albatrosses, but in 1996 the genus was split, with the mollymawks and the North Paci ...

es. It is named after, and originally devised in the late 1950s by,

John Douglas Gibson John Douglas Gibson ( – 21 May 1984) was a notable Australian amateur ornithologist who became an internationally respected expert on the Diomedeidae or albatross family. Gibson lived in Thirroul, New South Wales all his life, and worked at t ...

and other members of the

New South Wales Albatross Study Group The New South Wales Albatross Study Group (NSWASG) was an amateur ornithological Ornithology is a branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that relates to them." Several aspects of ...

. Gibson was an Australian amateur

ornithologist Ornithology is a branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that relates to them." Several aspects of ornithology differ from related disciplines, due partly to the high visibility and th ...

who carried out fieldwork on albatrosses along the coast of

New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...

for thirty years. The index assigns separate numerical values (from 1 to 6 with increasing proportion of white) to the degrees of colouration on four parts of the body - the back, head, inner wing and tail - of albatrosses to indicate variations in age and between different breeding populations. For instance, a bird with a completely brown back would receive a score of 1 for the back, while a bird with an all-white back would be scored as a 6. The index was later expanded by Pierre Jouventin and colleagues to cover the more complex patterning of the Amsterdam albatross, adding belly and tibial feather colouration. This system for categorising the wide and complex variation in appearance of great albatrosses has been instrumental in the discovery of several genetically isolated populations and consequent description of new taxa, and has made field identification easier.

References

{{reflist, 2 Ornithological equipment and methods Bird anatomy *