Black and Grey Petrels

Genus Procellaria

The Procellaria petrels represent a group of large and bulky seabirds that can be placed between the shearwaters of the genus Calonectris and the more fulmarine petrels.
Presently five species are recognized:

  • White-chinned Petrel or Shoemaker Procellaria aequinoctialis, circumpolar southern seas
  • Spectacled Petrel Procellaria conspicillata, mainly southern Atlantic Ocean
  • Westland (Black) Petrel Procellaria westlandica, New Zealand waters and southern Pacific Ocean
  • Parkinson’s or Black Petrel Procellaria parkinsoni, New Zealand and into tropical Pacific Ocean
  • Grey petrel or Pediunker Procellaria cinerea, circumpolar southern seas

Taxonomy

Until recently the largest of the Procellaria-species, the White-chinned and the only slightly smaller Spectacled Petrel, were considered to be conspecific. Now they are split into two separate species. Both have a large and strong bills, ivory colored with black sulci between the horny plates and ivory colored ungues, the latter sometimes slightly darker in the Spectacled Petrel. Specific identification based on skulls alone is probably not possible. Other morphological characteristics are indispensable.

The Westland and Parkinson’s Petrel are also two similar species, of which the latter is a smaller version of the first. Both have ivory colored bills (with a bluish tinge in young birds), with blackish ungues. In the Parkinson's the black is less extensive than in the Westland. There is no overlap in bill measurements. The Westland Petrel is of the same size as the White-chinned and its culmen is always longer than 47.8 mm. That of the Parkinson’s Petrel not longer than 45.1 mm
The bill of the somewhat distinct Grey Petrel is about the size of the larger Procellarias, with the same pattern as the White-chinned and Spectacled, but instead of ivory, more pearl-grey. The Grey Petrel's somewhat lighter bill structure comes close to that of the Calonectris species. Because its somewhat different coloration, habits and structure this species formerly formed a genus of its own: Adamastor. It is now considered to belong to Procellaria. 

Osteology

Skulls of this group show a certain similarity to those of the fulmars, but the intermediate position between these and the shearwaters is obvious because of their structure and the shape of some parts of skull and bill. Especially the lower mandible shows the typical concave unguis, like a shearwater’s bill. The lachrimal bones are not fused to the frontals as in the fulmarine petrels. The cranium of Procellaria has a rounded shape and rather shallow temporal fossae taking position between the shearwaters and the fulmars. The nostrils form a distinctive tube and are more like the fulmar’s than shearwater-like. Procellaria bills can have a flaky texture, increasing with age. 


White-chinned Petrel Procellaria aequinoctialis Falkland Islands.
Culmen: 52.2 mm; total: 119.7 mm, unsexed adult. Courtesey of J. Pompert, The Falkland Fisheries Department and W. v. Gestel

Parkinson's Petrel Procellaria parkinsoni Oakura, North Island, New Zealand.
Culmen: 40.5 mm; total: 95.2 mm, unsexed adult.

  • Skull
  • Flight apparatus
  • Pelvis and legs
  • Vertebrae and ribs

References

Photos:
Upper: White-chinned Petrel © Eric Preston
Lower: Parkinsons's Petrel  © Eric Preston