Antarctic Prion
Pachyptila desolata
The Antarctic prion has an overall length of 27 cm (11 in), a wingspan of 61–66 cm (24–26 in) and weighs 150–160 g (5.3–5.6 oz). Like all prions, its underparts are white and upperparts are blue-grey, with a dark "M" across its back to its wingtips. It has a white eyebrow, blue-grey bill, and blue feet. It also has a grey wedge-shaped tail with a black tip. On its wings, its greater coverts are near black. It is so similar in appearance to Salvin's prion that the two species cannot be distinguished at sea.
ID text from Wikipedia, CC BY-SA 4.0
Slender-billed Prion
Pachyptila belcheri
Like all prions, they are blue-grey above and white below with a dark "M" on their back to their wingtips. They have a white eyebrow and a dark line extending from below the eye almost to the neck. Their tail is wedge-shaped and grey with a black tip, their bill is blue-grey, and their feet are pale blue.
ID text from Wikipedia, CC BY-SA 4.0
Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Antarctic Prion and Slender-billed Prion.