Pelagodroma marina (Latham, 1790)

Size Measurements

The white-faced storm petrel (Pelagodroma marina) is typically 19 to 21 centimetres (7.5 to 8.3 in) in length, with a 41 to 44 centimetre (16 to 17 in) wingspan, and a body mass of 40 to 70 grams.

Limb and Bill Features

Key identifying features of this species include a dark bill, dark tarsi, dark toes, and dark claws.

Dorsal Plumage

It has pale brown to grey colouration on its back, rump, and wings, paired with black flight feathers.

Ventral and Facial Plumage

Its underparts are white, which distinguishes it from other north Atlantic petrels, and it has a white face marked by a black eye mask, similar to a phalarope.

Identification Ease

Its distinctive grey-brown dorsal plumage makes it one of the easier petrel species to identify at sea from a distance.

Sexual Plumage Similarity

Both sexes of this species (also called frigate petrel) have similar plumage with no seasonal variation in plumage.

Sexual Size Dimorphism

There are only slight size differences between the sexes: females are around 1–3% larger than males in tarsus, wing, and tail lengths, while males have a bill depth roughly 1.7% larger than females.

Juvenile Plumage Differences

Juveniles are similar to adults, but their fresh plumage typically has larger light fringes and tips on the upperpart feathers, and their overall appearance may be grey or brown depending on their moult stage.

Juvenile Tail Features

The tail fork of juveniles is also often shallower than that of adults, at least for the New Zealand subspecies P. m. maoriana.

Subspecies Morphological Variation

Different subspecies exhibit subtle morphological differences.

P. m. albiclunis Distinguishing Features

The Kermadec Islands subspecies P. m. albiclunis is similar to P. m. dulciae, but is set apart by its white rump and shorter, square tail, which distinguishes it from both P. m. dulciae and P. m. maoriana (both of which have pale grey rumps).

P. m. albiclunis Upper Tail Coverts

P. m. albiclunis also has white upper tail coverts instead of the typical grey found in other subspecies, making it highly distinct.

P. m. albiclunis Size

Additionally, P. m. albiclunis is slightly smaller in overall dimensions than P. m. dulciae.

P. m. albiclunis and P. m. dulciae Shared Traits

Both P. m. albiclunis and P. m. dulciae have square tails, and whiter faces and breast sides, than P. m. maoriana.

P. m. maoriana Tail and Breast Features

In contrast, the New Zealand white-faced storm petrel subspecies P. m. maoriana has a forked tail, and is characterized by dark patches on the sides of the breast.

P. m. maoriana Limb and Bill Measurements

It also has shorter culmen, tarsus, and middle toe (with claw) lengths than North Atlantic subspecies such as P. m. dulciae and P. m. albiclunis, and it has a longer tail than the average for other subspecies.

P. m. eadesi Plumage Features

The Cape Verde Islands subspecies P. m. eadesi has slightly paler plumage than P. m. hypoleuca, with a paler forehead and paler hindneck.

P. m. eadesi Beak and Neck Features

It also has a longer beak, measuring 18–20.5 mm compared to 16–19 mm in P. m. hypoleuca, and whiter neck sides that form an incomplete collar.