Procellariidae

Prions and Blue Petrel 

Prions

Prions are a race of abundant small petrels from the Antarctic and subantarctic region with very similar plumages: a white body, bluish grey upperparts with a dark M on the back and upper sides of the wings when seen from above. Although there is considerable difference in measurements, the main difference between the species lies in the shape of the bills. These vary from small 'pointed' via 'fulmarish' to extreme broad. Characteristic are the lamellae along the sides of the palate in all species. These form a sieving structure to filter  small food particles from the water. The development of these lamellae and grooves vary depending on the species. Bills of all Prions are bluish, except in the Broad-billed which has a blackish bill. This color comes from the tissue underneath the ramphotecal coating and is not retained in prepared skulls.

Characteristic for the skulls is the fusion of the lachrymal bones to the frontals, a feature that is shared with the fulmars, the Blue Petrel (Halobaena caerulea.) and the Pterodroma. petrels.  

The taxonomy of the Prions is difficult and possibly not yet fully understood. It is  mainly based on size and structure of the bill. But since there is a lot of intraspecific variability and intergradation between the recognized species and subspecies, the discussion on this topic is not closed yet. The list below shows the seven species that are accepted generally, including the recent separation of the MacGillivrayi's Prion. For more detailed information about the taxonomy and references see Warham 1990.

Identification of the Prions at sea is very difficult. Therefore much of the pelagic distribution is unknown.

Genus Pachyptila

• Broad-billed Prion Pachyptila vittata, Around subtropical convergence New Zealand, South Atlantic. 

• Salvin's Prion Pachyptila salvini:  south Indian Ocean, subantarctic to subtropics. 

• MacGillivray's Prion Pachyptila macgillivrayi, St. Paul's and Amsterdam I. Recently proposed split from T. salvini.

• Antarctic Prion Pachyptyla desolata, Almost circumpolar subantarctic and Antarctic. Three dubious subspecies:

•    P. d. desolata

•    P. d. maquariensis

•    P. d. banksi

• Fulmar Prion Pachyptila crassirostris; range at sea unknown. Two subspecies:

•    P. c. crassirostris, breeding islands south-east of New Zealand area.

•    P. c.. eatoni, Heard Is.

•    P. c. flemingi, Auckland Is. Recent subspecifc split (litt!)

• Fairy Prion Pachyptila turtur, probably circumpolar in southern oceans. Two subspecies:

•    P. t. turtur

•    P. t. subantarctica

• Thin-billed Prion Pachyptila belcheri, probably circumpolar between subtropics and Antarctic waters.

Skulls of Prions differ mainly by the size of the bill. See also the figure below (from Warham 1990).

The length of the culminicorn (i.e. distance between the nostrils and the rear end of the hook, or maxillary unguis) is an important measure to distinguish belcheri, turtur and crassirostris. In turtur this measure averages 5.1 mm (4.2 - 6.0), much shorter than in belcheri with an average of 9.2 mm, but not less than 8.3 mm.  In crassirostris the length of the culminicorn is 2 - 4 mm which is shorter than in turtur.

Antarctic Prion Pachyptila desolata, Baylyss Beach, North Island, New Zealand Total: 68.2 mm, unsexed adult. Ramphotecal coating not present.

Blue Petrel

Genus Halobaena

One single species that resembles the larger Prions in size and plumage. It shares also some anatomical features and characteristics of the structure of the bill such as the striae that resemble the lamellae of the Prions. These are obviously from the same origin. On the other hand the bill also resembles those of the genus Pterodroma  to which it might be related also. The lachrymal bones are fused to the frontals.

• Blue Petrel Halobaena caerulea, circumpolar southern Oceans.

Literature