Prions are notoriously difficult to identify at sea.
Here's good photos of six of the species!
This webpage is meant as an aide-memoire and for reference.
On the left a Broad-billed Prion
- photographed off Gough Island,
South Atlantic by
Ross Wanless
Note large head, strongly marked forehead, crown and ear coverts very dark. Supercilium small. Well marked M across wings. Bill usually black.
On the left a Salvin's Prion
photographed near
Marion Island, Indian Ocean
by Ross Wanless
Note head paler than Broad-billed Prion and bill blue. Most similar to Antarctic Prion and inseparable at sea, though bill is slightly longer and broader.
On the left an Antarctic Prion
- photographed by Nigel McCall whilst on a cruise to the Ross Sea, Antarctica
Note well-marked head; dark eye-stripe and ear coverts. Usually good clear supercilium and well marked M on upperwing. Colour and size of bill differ from Broad-billed Prion.
On the left a Slender-billed Prion
- photographed by Trevor Hardaker off Cape Town, South Africa

Note slim build with pale face and pale crown , long supercilium, narrow eye-stripe, narrow tail band.
On the left a Fairy Prion
- photographed off New Zealand by
Brent Stephenson
Note photo likely adult of nominate race. Rounded head has dark crown, eye-patch, short supercilium.  
On the left a Fulmar Prion
- taken by Malcolm and Michael Boswell whilst on a cruise of the New Zealand Subantarctic - the location was between Campbell Island and the Antipodes Islands
Note small size, pale appearance and short, heavy bill. Confusion with Fairy Prion, specifically race subantarctica which is as pale.