DIVERS (or LOONS) Gaviidae

DIVERS (or LOONS) Gaviidae

4 species

Fairly large to large, long-necked, low-bodied, cormorant-like diving birds of fresh and inshore coastal waters with dark upperparts and pale underparts. Normally appear tailless (although short tail can be elevated when bird at rest). Dive by slipping gently below surface, with slight forward roll. Not very gregarious but will form loose flocks away from breeding territories. In flight, have humpbacked appearance, with head and feet drooped below level of body. Flight swift and direct, often quite high, with rapid beats of strongly pointed wings. Normally visits land only when breeding, and then only immediate waterside. Generally silent outside breeding season. Feed mainly on fish.

Sexes similar. Marked seasonal variation. Juveniles resemble winter adults.

Partial post-breeding moult (complete in Red-throated) commences in late summer or early autumn and finishes by early winter. Complete pre-breeding moult (partial in Red-throated) takes place from late winter to spring. Post-juvenile moult virtually continuous during second calendar year, with adult plumage fully attained by second autumn or winter (apart from Yellow-billed, which has more complex and protracted moult and does not acquire full adult plumage until spring of fourth calendar year).

Divers (also known as loons) show an obvious white breast in all plumages, and when not in adult summer plumage also show extensive white on foreneck and face. On water, confusion likely only with the large grebes, cormorants and mergansers. Large grebes are shorter-bodied and longer-necked, with more abrupt, less gently sloping sterns. Cormorants have long, prominent tails, usually visible as bird dives, and tend to hold their heads angled upwards when swimming. Often (especially European Shag) jump well clear of water when diving. Cormorants also tend to look all-dark, but beware immatures with whitish or pale brown underparts. Adult female or immature mergansers show little or no white on foreneck, have solid brown head/hindneck, shaggy appearance to back of head and a white wing patch (sometimes obscured). In flight, large grebes and mergansers show conspicuous white patches on upperwing, while cormorants have slower wingbeats, carry their heads higher (so do not look humpbacked) and have conspicuously long tails.

Identification of adult summer-plumaged birds straightforward given reasonable views, but winter, immature and moulting birds more difficult. Identifying larger species in flight is particularly difficult. Points to concentrate on (for birds on water) are:

Pattern of head and neck • Head shape • Bill colour and shape • Contrast between neck and mantle
• Flank pattern