Parasitic Jaeger

The Parasitic Jaeger is an incredibly fascinating bird. True to their name, they are kleptoparasitic birds which means that they steal the food of other birds. They commonly chase Gulls and Terns until they are forced to drop their food, after which they swoop in and catch the feed. They inhabit and breed in coastal or tundra regions with dense populations of other birds so that they can easily obtain their food.

About Parasitic Jaegers

Jaeger birds are named after the German word jger, meaning hunter. These birds might be commonly confused with other Jaegers such as the Long-tailed and Pomarine Jaeger, but there are characteristics that we will delve into that make them unique. They also come in two distinct color patterns, which we call light and dark morphs. Parasitic Jaegers are also known by the name Arctic Skua and belong to the seabird Skua family.

● Parasitic Jaeger Photos, Color Pattern, Song
● Parasitic Jaeger Size, Eating behavior, Habitat
● Parasitic Jaeger Range and Migration, Nesting

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Parasitic Jaeger Color Pattern

Parasitic Jaegers have two main color patterns- a light morph and a dark morph, with some intermediates. The presence of two distinct morphs has been linked to mutations. Light morphs have brown upperparts, blackish-brown caps and white collars with white underparts. Their necks are white with yellowish shading on the sides. Their breasts can have brown bands, either complete or partial. There is a large degree of variation among light morphs, and these birds can be dusky or closer to intermediates.

Dark morphs have a similar color pattern, but have white patches on their heads and brown underparts. Intermediates follow a similar color pattern, but have white patches on their bellies and paler collars. They also have yellow shading on their necks, just like the light morphs.

Across all morphs, these Jaegers have whitish-gray shafts of their outermost primaries, whitish areas on the base of the undersides of their wings, brownish underwing coverts and pointed central rectrices that protrude past the tail.

The juveniles have a high degree of variation between the light and dark morphs. The plumage of the dark morphs is dark brown, lighter brown and gray, The light morph juveniles have brown, golden brown and cream barred plumages. Approximately half of the birds have orange-brown barring on their backs.

Description and Identification

Parasitic Jaegers can easily be mistaken for Pomarine and Long-tailed Jaegers because of their similar size. This section will help you distinguish one from the others.

Adults in their definitive alternate plumage have elongated, pointed central rectrices. This distinguishes Parasitic Jaegers from Pomarine Jaegers. The rectrices are not as long or flexible as that of Long-tailed Jaegers, which is another feature to note while trying to identify them.

Parasitic Jaegers do not have the broad-winged, heavy chested anatomy of Pomarine and Long-tailed Jaegers. Parasitic Jaegers usually have 4-6 shafts, which is more than the Long-tailed Jaegers on average.

Light morphed Parasitic Jaegers have a stronger contrast between their brown and white areas from the Pomarine Jaeger, and lack the white forehead spot and contrast between their upperwing coverts and remiges, which distinguishes them from Long-tailed Jaegers.

Juveniles can be extremely tricky to correctly identify because of the high degree of variation between the two morph extremes. As we mentioned before, some Parasitic Jaegers have orangish or cinnamon barring on their necks and back, which can set them apart from immature Pomarine Jaegers, who have tan or whitish barring. Immature Parasitic Jaegers also lack the double white flashes on the underside of the wings, unlike Pomarine Jaegers.

Like the adults, immature Parasitic Jaegers have more white shafts than the immature Long-tailed Jaegers. However, we need to be careful while counting these shafts because some have sharper definition than the others.

Parasitic Jaeger Song

Parasitic Jaegers have several different calls, and we need to research their vocalizations more to have more accurate knowledge on the subject. Their long call consists of up to 12 two-syllable notes at a speed of approximately 1.3 notes per second. The call is a low pitch, nasal call, that sounds like a mewing “nyeeAh-nyeeAh-nyeeAh”. This call can be preceded and succeeded by other low pitched, subdued notes as the birds pick up or cool down their vocal momentum. They make this call from the ground or mid-air during flight to acknowledge other members of their species passing by. They also make this call to mark the end of pursuit flights, when the rivals separate to return to their territories.

It is important to note that their long call increases in pitch as they warm up, as compared to the long call of the Long-tailed Jaegers, who have a falling pitch. The long call often comes before the short call. The short call consists of staccato or fragmented notes in an irregular arrangement. You can also hear the short call during aerial displays or pursuits. It is often in response to an attacker.

Other notes let out by these birds sound like a yelping “kyeew! kyeew!”, a shorter “kiuk!” and a longer disyllabic “kyeew-ew!”. Another vocalization is a trill series of “kek-kek-kek-kek” notes. You can hear these vocalizations when the birds are under attack or in the view of a predator.

Various other important calls include the adult male’s copulation call, and the corresponding female’s purring call. They also have a squeaking call, which is a hissing call initiated with a squeak, often let out during nest building. They have a begging call used during their courtship ritual of feeding. When birds at sea feed on offal, they may let out high pitched “weet-weet” notes. These birds remain silent while pursuing other species for food.

Parasitic Jaeger Size

The average length of Parasitic Jaegers, across sexes is about 14.6-20.9 inches. Their average weight is 10.6-20.6 ounces, and their average wingspan is 42.5-46.5 inches.

On the size spectrum of Jaegers, they fall between the size of smaller Long-tailed and larger Pomarine Jaegers. Females can be 15-20% larger than males.

Parasitic Jaeger Behavior

These birds are agile kleptoparasitic birds, and migrant birds can fly as high as 5-10 meters above the ground or sea level. They can swim readily, but they don’t dive.

When members of their own species intrude their territory, they take an aggressive upright stance, extending their necks vertically and keeping their beaks horizontal. This posture is to intimidate and discourage the other birds from advancing further. When intimidated, these birds take an intimidated upright posture, extending their necks vertically and angling their beaks upward. They usually back away or escape the territory following this.

Aggressive interactions on occasion can involve them pecking at the ground, or intensive preening. Parasitic Jaegers can also attack intruders in mid-air. The attacker bird swoops from above at a high speed, and can also strike the intruder with their feet. After the intruder has been knocked down, they crouch to face their rival. Next, they fight each other by facing each other and fight each other with their feet.

Parasitic Jaeger Diet

These birds have a diet consisting primarily of fish, birds and rodents. True to their name, they are kleptoparasitic birds- in other words, they steal food from other birds. In coastal or sea-proximal habitats, they mainly steal and eat fish. On land, they eat several small birds and their eggs, along with rodents, insects, berries and small fruit. They do their foraging at sea by chasing other birds into dropping their foraged food, and swoop to catch it. Parasitic Jaegers also dip down to catch fish on the surface of water or the coast. They feed while walking. They come under the category of kleptoparasites, but they also forage and hunt themselves.

Parasitic Jaeger Habitat

Parasitic Jaegers are marine birds and their habitats are predominantly coastal. They gravitate towards site such as estuaries that attract terns and small gulls, particularly for their food.

Parasitic Jaegers often migrate over land instead of the sea. They breed on wet tundra, moorland or grassland. They often breed near other coastal seabird colonies to rob them of their food. If this isn’t possible, they make do in areas of low nesting densities to forage themselves. Their nests can be placed in low-lying, wet tundra, often near a lake or river.

Their breeding ranges are more extensive than the Long-tailed and Pomarine Jaegers. Unlike the Long-tailed Jaeger, they breed near rivers and lakes. In northern Alaska, they have been recorded to occupy low-lying, marshy tundra and
drier tussock-heath tundra near the coast and in the foothills of the Brooks Range. They are also found in Northeast Greenland, where they breed near the mouth of fjords and also along the outer coast, again near lakes. In Iceland, they breed throughout the island.

Range and Migration

These birds are long distance migrants. They fly from their breeding range in Arctic and Subarctic regions, to their wintering range in tropical or southern temperate oceans. They typically migrate near coasts, but can also migrate over land. Small numbers of their populations can spend the winters in the Northern Hemisphere. Contrastingly, some of them also choose to stay in the Mediterranean and coastal Atlantic year-round.

Unlike the other members of the Jaeger family, they rarely make large movements on the arctic coast, and scarcely migrate on the north coast of the Chukchi Peninsula. The adults leave the breeding ranges before the juvenile birds. They typically depart from July onwards. Some birds travel to the far offshore side.

Parasitic Jaeger Lifecycle

We have little information on their hatching and phenology of their development. We know that it is common for the parents to leave their chicks unguarded when they leave their territory to gather food. In northern Alaska, both parent birds have been recorded to be absent from the nest for 50% of the day, whereas this proportion of time was only 8% for birds studied in the Anderson River delta.

The hatchlings enter the chick stage and remain on their parent territories for up to 2-3 weeks after they have fledged the nest. This usually takes place in the first week of September.

Once the migration season has begun, the young seldom stay with their parents. There are outlying reports of an adult Jaeger feeding their young ones during migration. In southern Spain, migrating juveniles are often unsuccessful in attacking Gulls and terns for food.

Nesting

Their nest-building process is initiated by the male of the pair, who walks or flies towards an appropriate site and emits the nest call. At the site, both birds begin to squeak and peck at each other’s beaks. The female then proceeds to build the nest by scraping the ground.

As mentioned before, these birds choose wet areas of tundra. They also prefer slightly elevated sites. The nest itself is a slight depression in the ground made by scraping from the female’s feet and breast. On occasion, it is lined with dry grass or lichen.

Anatomy of a Parasitic Jaeger

Parasitic Jaegers have hooked bills which lets them effectively scoop up their feed. They also have webbed feet and a white patch on their wings’ underside. They have pointed central rectrices that protrude past their tail feathers. During the nonbreeding season, they lose their central tail feathers. The anatomy of both sexes is almost identical.

Final Thoughts

These birds are wonderfully intriguing creatures. Parasitic Jaegers are the among the most intensively studied seabirds, but there are still areas for us to study further. We must study more about their hatching and phenology to understand them better. Thankfully, these birds are not endangered. They are the most commonly sighted Jaegers. However, we do not have a precise count of their worldwide population. We must also study the biology of their Arctic populations in better detail.

Ornithology

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