Stercorarius pomarinus (Temminck, 1815)

Species Naming

This species, Stercorarius pomarinus, measures 46 to 67 cm (18 to 26 in) in total length, has a wingspan of 110 to 138 cm (43 to 54 in), and weighs 540–920 g (1.19–2.03 lb).

Breeding Adult Tail Feature

The upper end of the total length range includes the elongated 10 cm (3.9 in) tail streamer that develops on breeding adults.

Identification Difficulty

Identifying this jaeger is difficult because it closely resembles the parasitic jaeger, and it occurs in three distinct plumage morphs.

Body Size Comparison

Pomarine jaegers are larger than common gulls. Compared to parasitic jaegers, they are much bulkier, have broader wings, and are less falcon-like in shape, though they share the same wide range of plumage variation.

Flight Characteristics

Their flight is more steady and slower-paced than that of the smaller parasitic jaeger.

Vocalizations

This species produces many harsh chattering calls, along with other calls that sound like "which-yew".

Light Morph Adult Plumage

Adult light-morph pomarine jaegers have a brown back, mostly white underparts, and dark primary wing feathers marked with a white "flash". Their heads and necks are yellowish-white with a black cap.

Dark & Intermediate Morph Plumage

Adult dark morph individuals are solid dark brown, while intermediate morph birds are dark overall with slightly paler underparts, heads, and necks.

Shared Morph Wing Feature

All three morphs have the characteristic white wing flash, which appears as a distinctive double flash on the underwing.

Breeding Adult Tail Structure

In breeding adults of all morphs, the two central tail feathers are much longer than the other tail feathers, with a spoon shape and a twist away from the horizontal orientation.

Juvenile Identification Challenge

Juvenile pomarine jaegers are even more challenging to identify, and cannot be easily distinguished from juvenile parasitic jaegers at a distance based on plumage alone.