{"id":4752,"date":"2022-10-07T16:54:39","date_gmt":"2022-10-07T16:54:39","guid":{"rendered":"https:\/\/wordpress.viu.ca\/biol325\/?p=4752"},"modified":"2022-10-07T16:54:39","modified_gmt":"2022-10-07T16:54:39","slug":"parasitic-jaeger-the-avian-pirate","status":"publish","type":"post","link":"https:\/\/wordpress.viu.ca\/biol325\/2022\/10\/07\/parasitic-jaeger-the-avian-pirate\/","title":{"rendered":"Parasitic Jaeger: The Avian Pirate"},"content":{"rendered":"\n

As you are scanning the ocean looking for shorebirds you notice something strange through your binoculars. It\u2019s a gull, not an uncommon sight, but its erratic flight patterns are. It\u2019s twisting and turning even flying straight up as high as it can go, it looks as if it is trying to escape something. You look around more and that\u2019s when you see it, a dark flash pursuing the gull, the avian pirate, the bully of the seas, the parasitic jaeger. Enamored by the chase you can\u2019t help but watch. After an exhausting chase the jaeger finally catches its victim and collects its hard-earned meal, straight from the gullet of the gull.<\/p>\n\n\n

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Figure 1: Parasitic jaeger and black-legged kittiwake engaged in aerial combat. Photo by Doug Gochfeld<\/a>.<\/figcaption><\/figure>\n<\/div>\n\n\n

Description & Identification<\/h2>\n\n\n\n

The parasitic jaeger (Stercorarius parasiticus<\/em>), also known as the arctic skua in Europe, is a member of the order Charadriiformes (the shorebirds) and the family Stercorariidae (the skuas). It is a relative of the gulls and as such bears a similar appearance. They breed in the arctic tundra and spend the winter in southern and tropical seas. During the breeding season their diet consists of generally whatever they can find, including fish, insects, small mammals, berries, carrion, and other birds (AllAboutBirds<\/a>). During the rest of the year, their diet becomes far more unique, they get most of their food by stealing it from other seabirds, also known as kleptoparasitism. This is where their name comes from and it can have significant negative effects on the victimized seabirds (Simeone et al.<\/em>, 2014; Jones et al.<\/em>, 2008). <\/p>\n\n\n\n

Identification of the parasitic jaeger can be quite difficult. It has three different morphs: a dark morph, a light morph, and an intermediate morph (Janssen et al<\/em>., 2005) and there are also two other jaeger species in British Columbia, the pomarine jaeger (Stercorarius pomarinus<\/em>) and the long-tailed jaeger (Stercorarius longicaudus<\/em>) (AllAboutBirds<\/a>). Luckily, the parasitic jaeger is the most common to be seen from shore (Sibley, 2016).<\/p>\n\n\n\n

Visually the things to look out for when identifying the parasitic jaeger are size, tail length, and wing tips. The parasitic jaeger is the middle size of the three jaegers, with the pomarine being the largest, and the long-tailed being the smallest. They will have a long-pointed tail, but still shorter than the long-tailed jaeger. The last diagnostic feature is the number of white bars on the wing tip. This follows a similar trend to size where the pomarine will have the most, the parasitic will have 4-6 (one on each outermost feather) and the long-tailed will have the least (AllAboutBirds<\/a>; Sibley, 2016).<\/p>\n\n\n\n

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Figure 2: Left: Dark morph of the parasitic jaeger. Photo by Ian Davies<\/a>. Right: Light morph of the parasitic jaeger. Photo by Eric Gofreed<\/a>. Notice the long tail and the white bars on the top-side of the outermost wings.<\/figcaption><\/figure>\n<\/div><\/div>\n<\/div>\n<\/div>\n\n\n\n

As for sounds, they are generally quiet birds, but they do have two common calls. The first is their main call that is a series of nasally two-parted notes that is heard most often during breeding in the arctic. The second is an irregular, sharp, separated note that is often heard during an attack or chase (Audubon<\/a>; AllAboutBirds<\/a>).<\/p>\n\n\n\n

Audio 1: A collection of common parasitic jaeger calls. From Audubon<\/a>.<\/figcaption><\/figure>\n\n\n\n

Behaviour<\/h2>\n\n\n\n

Parasitic jaegers will generally first start breeding at the age of four or five and tend to nest as isolated pairs or small colonies. Mates are chosen by the female based on a flight display by the male accompanied by calls, upright posturing, and supplying of food. After mating, the male will find a nest location on the ground, often on a slant, and the female will build a nest in a shallow depression using plant material. Jaegers lay one to three olive to brown eggs and incubation takes place for about a month by both parents. During which they are quite territorial and often defend their nests (Audubon<\/a>).<\/p>\n\n\n\n

As the namesake of the species, kleptoparasitism is one of the most notable behaviours of the parasitic jaeger. This is when a jaeger will chase another bird, often a tern or gull, until it regurgitates or spits out its food (Dakota, 2009<\/a>). The jaeger will first fly low to the ocean camouflaging with its dark plumage. Once in position, the jaeger will try to surprise the victim to make them drop the food. If this does not work, then the jaeger will instead try and chase the bird until it drops its food. Although the jaeger harasses other birds, it rarely results in a physical attack (Taylor, 1979, as cited in Dakota, 2009<\/a>). This technique is not flawless though, many birds have learned to counter it by foraging in large groups and mobbing any jaegers that pose a threat (Dakota, 2009<\/a>). <\/p>\n\n\n\n

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