E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Stercorarius parasiticus (Linnaeus, 1758)
Parasitic Jaeger
Family: Stercorariidae

Species account author: Jamie Fenneman

Photo of species

© Tim Zurowski  Email the photographer   (Photo ID #12772)

Distribution of Stercorarius parasiticus in British Columbia.
(Click on the map to view a larger version.)
Source: Distribution map provided by Jamie Fenneman for E-Fauna BC

Species Information

Breeding adult
Breeding plumage is held primarily between March and November, and thus virtually all adults observed in B.C. are in breeding plumage. This species occurs in two colour morphs (as well as intermediates), with the light morph dominating in B.C. All colour morphs share similar bare part colouration (dark iris, blackish bill, and blackish legs and feet). Light morph: The upperparts (including the upperwings) are uniformly dark brown, slightly darker on the flight feathers, with white shafts on the primary feathers that produce a pale flash when in flight. The short tail is dark blackish-brown with the central pair of feathers noticeably elongated and pointed, producing a distinctive tail shape. The underparts are primarily whitish, with dark brown undertail coverts, lower belly, and flanks and a partial (and variable) dark brown collar across the upper breast (typically confined primarily to the sides of the breast). The underwings are uniformly dark, except for a prominent white patch across the base of the primaries. The crown, forehead, lores, and area below the eye are dark blackish-brown, contrasting sharply with the pale whitish (and often yellowish-tinged) sides of the face, neck, and throat; there is also a narrow pale crescent above the base of the upper mandible. Dark morph: Dark morph adults are uniformly dark blackish-brown, usually with slightly darker crown and forehead, but still show whitish primary shafts and a prominent white patch across the base of the primaries on the underwing. Many individuals are intermediate in colour between the light and dark extremes of plumage.

Non-breeding adult
This plumage is held between November and March, and is very rarely observed in British Columbia. Light morph: Non-breeding plumage is similar to breeding plumage, but the underparts tend to show more brownish barring on the sides of the breast, sides, flanks, lower belly, and undertail coverts, and the uppertail coverts are barred with whitish. In addition, the head pattern is less sharply defined and the upperparts show narrow pale fringes on many of the feathers. Dark morph: This plumage is essentially identical to the breeding plumage.

This plumage is acquired in late summer of the first year and retained through the following winter (typically lost by March). Most individuals observed in B.C. are light morph or intermediate plumages. All colour morphs share similar bare part colouration (dark iris, blue-grey or flesh-grey bill with a dark tip, and greyish or flesh-grey legs with blackish feet). Light morph: Upperparts, including the back, scapulars, upperwings, and rump dark blackish-brown with broad buffy to cinnamon-coloured feather edges, forming a barred or scalloped pattern across the upperparts. The short tail is blackish-brown with slightly elongated central feathers that form a short point. The underparts and underwing coverts are buffy to cinnamon-buff and are heavily barred with blackish-brown. There is a bold white patch across the base of the primaries on both the upperside and underside of the wings. The head and neck are buffy to cinnamon-coloured and finely streaked with dark brown throughout. Dark morph: This plumage is uniformly dark blackish-brown, with variable (usually minimal) very fine paler brown edges on the feathers of the upperparts and very fine, indistinct paler brown barring on the underparts. A prominent white patch is present across the base of the primaries across both the upperside and, especially, underside of the wings.

Second- and third-year immatures
Acquisition of adult plumage takes three years in this species, and it undergoes a series of plumages during this time that gradually become less like the brown juvenile plumage and more like the true adult plumage. See Olsen and Larsson (1997) for more detailed discussion of these infrequently-observed plumages.

Total Length: 41-50 cm
Mass: 350-540 g (f >m)

Source: Olsen and Larsson (1997); Sibley (2000)



Identification of all jaeger species is a complicated procedure, particularly for immature birds. Parasitic Jaeger is intermediate in size and structure between the smaller, more slender Long-tailed Jaeger and the larger, bulkier Pomarine Jaeger. As a result, many identifications rely on subtle differences in structure and flight style rather than plumage characteristics. Long-tailed Jaeger tends to have a more tern-like flight than the falcon-like flight of Parasitic Jaeger, while Pomarine Jaeger has a distinctly gull-like flight style. These characteristics require extensive experience with all three species, however, and are unlikely to be reliable except by very experienced field observers. All adult Parasitic Jaegers show two short, pointed central tail feathers that extens past the tip of the tail. In comparison, Long-tailed Jaeger has very long, pointed central tail feathers, while Pomarine Jaeger has heavy, round-tipped, spoon-shaped central tail feathers.

Light-morph adult Parasitic Jaeger has dark brown upperparts that are intermediate in colour between the paler greyish-brown upperparts of Long-tailed Jaeger and the darker blackish-brown upperparts of Pomarine Jaeger. Light-morph Parasitic Jaeger tends to show a smudgy partial brown band across the breast, whereas Long-tailed Jaeger shows little or no dark breast band and Pomarine Jaeger shows a variable, but usually heavy, dark blackish-brown breast band. The amount of white on the shafts of the primaries of adult Parasitic Jaeger is also intermediate between the other two jaeger species (less white in Long-tailed, more white in Pomarine). Finally, additional field marks include the all dark bill (Pomarine has a bicolored bill), minimal contrast betweent he colour of the upperwing coverts and flight feathers (flight feathers considerably darker and blacker in Long-tailed), the small pale area above the base of the bill (lacking in either of the other jaeger species), and the brownish-black cap (blacker in both other jaeger species).

Due to the complexities of jaeger identification, only certain field marks pertaining to the most commonly-observed adult plumage (light morph) will be discussed here. For further information, including a discussion of immature and dark-morph plumages, readers are directed towards references such as Sibley (2000) or Olsen and Larsson (1997).

Generally silent at sea, although it may utter a high-pitched weet, weet when feeding on offal. The most commonly-heard calls on the breeding grounds include a nasal KEwet, KEwet…and a short, barking gek. Also gives a “long call” during courtship, which is a series of 1-12 nasal, whining or crowing, bisyllabic feee-leeerrrr notes given at a rate of ~1.3 notes/sec.

Source: Wiley and Lee (1999); Sibley (2000)

Breeding Ecology

Pair formation occurs on the breeding grounds. Courtship involves a variety of vocal and behavioural displays, generally beginning with the unpaired male assuming an upright posture as a potential mate apporoaches. During initial contact, the female approaches the male and throws her head back with her bill open; the male responds by bowing his head, raising his tail, and calling loudly. Both birds also emit squeaking calls during this initial encounter. Prior to copulation, the male often engages in courtship feeding and associated behavioural displays, such as lowering of the neck.

The nest consists of a shallow depression in the ground that is sometimes lined with small amounts of dry grass or lichens; some individuals lay eggs directly on bare ground. The nest depression is created by the female and is typically placed in open areas away from cover, sometimes on a low mound or hummock.

A single clutch of (1) 2 eggs is laid by the female in late May or early June and is incubated by both sexes for 24-28 days before hatching. The smooth, slightly glossy eggs are dull olive or buffy (often tinged with green, grey, or brown) with variable spots, blotches, and lines of brown and/or grey that are either evenly distributed or are clustered towards the larger end. Very rarely, some eggs may show a pale blue ground colour. Eggs likely occur in British Columbia between late May and late June.

The young are semi-precocial and downy at hatching, with thick, soft, dark brown to blackish-brown down that is paler and tinged with grey around the eyes, on the chin, on the belly, and at the tips of the wings. Differences between light morph and dark morph individuals are often apparent even at the nestling stage. The short bill is grey with a darker tip and the legs and feet are blue-grey. The young are tended at the nest by both adults for 1-2 days after hatching, but quickly disperse into nearby areas. They are capable of flight by 28-33 days of age, and become fully independent within 7-8 weeks of hatching.

Source: Baicich and Harrison (1997); Wiley and Lee (1999)
Foraging Ecology

The Parasitic Jaeger, as with all other jaegers, specializes in kleptoparasitism as a foraging method throughout much of the year. During the breeding season, this species relies less heavily on kleptoparasitism and preys primarily on small birds, small mammals, and eggs that are obtained near the nest site in upland or riparian habitats; other food items such as carrion, berries, insects, and fish are also sometimes consumed in small amounts during the breeding season. Outside of the breeding season, however, kleptoparasitism is the primary means of obtaining food items such as fish, marine invertebrates, and offal. During bouts of kleptoparasitism, the jaeger targets a smaller species such as a storm-petrel, tern, or small gull (Bonaparte’s Gull, Sabine’s Gull, Black-legged Kittiwake) and pursues it mercilessly until the individual disgorges its last meal, which is subsequently consumed by the pursuing jaeger. Although kleptoparasitism accounts for nearly 90% of all foraging activities by individuals outside of the breeding season, this species does also occasionally acquire food items independently by picking them from at or near the surface of the water, and it sometimes pursues and captures small passerines that are migrating over the ocean.

Source: Olsen and Larsson (1997); Wiley and Lee (1999)


Breeding birds are found along riverine gravel bars, in sedge or grass meadows, and in open willow-birch scrub. Outside of the limited breeding range, this species is observed primarily during migration along coastal B.C. During migration, it frequents both nearshore and offshore marine waters where it is found in habitats such as exposed coastlines, coastal headlands, sheltered straits and channels, coves, estuaries, surge narrows, bays, and even sewage outfalls; it occasionally occurs over large coastal lakes or at the heads of inlets and fiords. Offshore migrants occur both over the continental shelf as well as beyond the continental slope over deepwater habitats. Inland vagrants typically occur on large, deep lakes. Wherever it occurs, the Parasitic Jaeger is most frequent in areas that support congregations of species such as Bonaparte’s Gull, Black-legged Kittiwake, Mew Gull, Sabine’s Gull, Arctic Tern, and Common Tern.

Source: Campbell et al. (1990b); Wiley and Lee (1999)


Global Range

Breeds in arctic areas of North America, Greenland, and Eurasia. In North America, breeding populations occur from south-coastal Alaska east to Nunavut (including north through the Arctic Archipelago), northern Manitoba, northern Ontario, northern Quebec, and northern Labrador. Winters primarily at sea in the southern hemisphere and in tropical regions, although small numbers occasionally occur north into North American waters (California, Florida, Gulf of Mexico, etc.).
BC Distribution

Uncommon along the lower Tatshenshini and Alsek Rivers in extreme northwestern B.C., where it has only recently been detected breeding.

Casual during winter (December-early January) in the Strait of Juan de Fuca and southern Georgia Strait, although most/all of these records likely pertain to exceptionally late fall migrants rather than true overwintering birds.

Migration and Vagrancy
Uncommon spring and fairly common fall migrant in all marine waters along the coast, including both nearshore and offshore waters (as well as occasionally on large coastal lakes). Casual spring and very rare fall migrant throughout the interior, most commonly around Shuswap Lake and Okanagan Lake in the south-central interior. Accidental in summer (June) in the southeastern interior (Creston).

Spring migration along the entire coast is very brief, occurring primarily from mid-May to early June and peaking in late May (occasional individuals occurring as early as early April or lingering as late as late June). The few observations of spring migrants in the interior (Okanagan Valley, Creston area) have all occurred in late May, which is consistent with the peak coastal movement. Individuals arrive on the breeding grounds in May and early June.

Fall migration is considerably more protracted than spring migration, with the first individuals departing the breeding grounds in July and the bulk of the population dispersing through August and early September. The first southward-bound migrants detected along the coast in late July or early August (occasionally in mid-July), with peak occurrence from late August to early October; some later individuals occasionally linger into early or mid-November (exceptionally into December). Fall migrants in the interior occur primarily from late August (occasionally July in northeastern B.C.) to mid-October (exceptionally into November), which is again consistent with peak movements along the coast.

Source: Campbell et al. (1990b); Kenyon et al. (2009)


Population and Conservation Status

This is the most frequently encountered jaeger species in British Columbia nearshore waters, and is thus the species that is most familiar to land-based observers. It is also a globally-secure species, with worldwide population estimates as high as 1,000,000 birds. As a result, it is not recognized as a species of conservation concern by either the B.C. CDC (Conservation Data Centre) or COSEWIC (Committee on the Status of Endangered Wildlife in Canada).

Source: Wiley and Lee (1999)


This species is monotypic, with no recognized subspecies.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
NativeS1B,SUMRedNot Listed
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Additional Range and Status Information Links

Additional Photo Sources

General References

Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2021. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 2023-09-24 1:22:04 PM]
Disclaimer: The information contained in an E-Fauna BC atlas pages is derived from expert sources as cited (with permission) in each section. This information is scientifically based.  E-Fauna BC also acts as a portal to other sites via deep links.  As always, users should refer to the original sources for complete information.  E-Fauna BC is not responsible for the accuracy or completeness of the original information.

© E-Fauna BC 2021: An initiative of the Spatial Data Lab, Department of Geography, UBC