Gaviidae

Divers or Loons


The group of the Divers or Loons, as they call them in North America, is formed by five species exclusively from the Northern Hemisphere. All of them are rather large birds, breeding in the arctic and boreal zone of Eurasia and North America. Although ranges overlap a great deal, identification is pretty straightforward. The bills are so distinctive that it is easy to tell them apart.
The Great Northern and the White-billed Diver, both the larger of this group, are more or less similar in appearance by their plumages, black headed and intensively spotted white on the backs in summer and greyish in their juvenile and winter plumage. The main difference is formed by their large bills which are straight and black in the Great Northern and yellowish white and somewhat 'upturned' in the White-billed.
Until recently the smaller Black-throated and Pacific Diver were considered subspecies of a single grey-headed and black-throated circumpolar species, but are now separated. Both have straight dark bills, in the slightly smaller Pacific Diver a little bit shorter.
The Red-throated Diver is the smallest of all, but also a grey-headed with - as the name says - a red throat in summer. Its bill is less heavy, but the main difference is its upturned appearance. Winter and juvenile plumages of the latter species are also greyish.
Skulls of all divers have very pronounced depressions for the nasal glands above the eyecases and strongly developed supraorbital ridges. Like in the auks this ridge becomes thicker with age. In all species bills of juvenile and first winter birds are not as heavy as in adult birds and the lachrimal bones are not fused to the nasal bones yet.
 

Genus Gavia
  • White-billed Diver or Yellow-billed Loon Gavia adamsii, high North of North America and Siberia, moving south in winter.
  • Great Northern diver or Common Loon Gavia immer, northern North America, southward and European coast in winter.
  • Black-throated Diver or Arctic Loon Gavia arctica, two subspecies:
  •   G. a. arctica, northern Europe east to Lena river. European coast and Mediterranean in winter.
  •   G. a. viridgularis, from Lena River eastward into Siberia.
  • Pacific Diver or Pacific Loon Gavia pacifica, eastern Siberia, Alaska, Canada to Baffin I.
  • Red-throated Diver or Red-throated Loon Gavia stellata, circumpolar in the high North, moving south in winter.
     
    • White-billed Diver Gavia adamsii

    Terschelling, The Netherlands

    Culmen: 91.8 mm; total: 185 mm; adult female 
    Great Northern Diver Gavia immer

    Hampton, VA, USA

    Culmen: 74.4 mm; total: 159 mm; adult female

    Summer bill
    Great Northern Diver Gavia immer

    The Netherlands

    Culmen: 75.7; total: 159 mm, adult female

    Winter bill

    		Black-throated Diver Gavia arctica arctica

    Vlieland, The Netherlands

    Culmen: 55.0 mm, Total: 131.4 mm, 1st winter

    		Red-throated Diver Gavia stellata

    The Netherlands

    Culmen: 57.0 mm, Total: 126.3 mm , adult male

    Skeleton

    Literature: