Arctic Jaeger (Stercorarius parasiticus)

Key Facts

• Latin name: Stercorarius parasiticus
• IUCN status: Least Concern (Global) – Endangered (Europe)
• Global population: The global population is placed in the band 400,000-600,000 mature individuals. The European breeding population is estimated at 27,100–41,500 pairs (54,200–83,000 mature individuals).
• Migration Route: Atlantic Ocean flyway, Central Asian Flyway (population breeding in northern Russia), Americas Flyway (Atlantic)

Description

• Wingspan:  107–125 cm 
• Life span: Up to 33 years (oldest individual recorded), few records of individuals who lived more than 20 years 
• Distinct features: Arctic Jaegers come in different colours – lighter and darker plumage. The dark morph prevails in the southern parts of its range. They are almost completely dark brown, apart from pale wingtips. The light morph predominates in the northern regions. They have a dark cap, and the back and the tail contrast with a yellowy-white underside and neck. Overall, the Arctic Jaeger’s flying style is more like a falcon.
• Favourite food: Most of their diet during winter and migration consists of fish acquired by robbing other birds. This act is also known as kleptoparasitism.
• Top Speed: Up to 50 km/h
• Habitat: Moorland, coastlines, islets and open sea.

Flight for survival

Arctic Jaegers, also called Arctic skuas, are known to be acrobatic flyers. At sea, they can be seen flying low and fast over the waves in impressive pursuit of prey. But these forceful sky artists have two faces.  At their breeding grounds on land, they are very aggressive – dive-bombing anyone who gets close to their nests. When the breeding ends, Arctic Jaegers embark on spectacular migrations, some wintering in the Canary Current off West Africa, while others travel further into the southern hemisphere, wintering off south-west Africa or south-east South America, and covering distances of over 10,000 km.

Nowadays, Arctic Jaegers are among Europe’s most endangered seabirds, experiencing one of the fastest population declines of all seabird species in the UK. The species faces increasing threats at their breeding and wintering sites and at refuelling areas such as the mid-North Atlantic Ocean, where they stop to rest and feed during their journeys during spring migration. Human persecution is a local problem in some areas of Northern Europe. Wind energy production, fisheries and rising temperature extremes all pose pressure, and the species has been classified as highly sensitive to changes in sandeel populations, with decreases in sandeel stocks causing declines in the northernmost Scottish population.

BirdLife’s work

Through its marine programme, the BirdLife Partnership is committed to tackling the main threats on land and at sea for dwindling seabirds. In the past decades, our UK partner RSPB has campaigned tirelessly to close industrial sandeel fisheries. Sandeels are a core food source for many seabirds and sea mammals and their decline has a huge negative effect on top predators and the whole marine ecosystem.  In 2024, we celebrated a historic win as the UK’s and Scottish governments decided to close industrial sandeel fisheries in their waters, great news for seabirds, including Arctic Jaegers. But, things are still far from safe. At the end of October, the European Commission triggered an Arbitration tribunal to assess compatibility of the closure with the EU–UK Trade and Cooperation Agreement (TCA). The RSPB and BirdLife Europe prepared a joint NGO statement to respond to this move by the European Commission and highlight again the importance of this vital measure taken by the UK and Scottish Governments to build resilience in seabird populations and wider marine biodiversity.

Interesting facts

The pirates of the seas

The powerful and agile Arctic Jaegers, as indicated by their scientific name, are widely regarded as the pirates of the seas, chasing other seabirds (such as puffins, terns and gulls), and stealing the fish they have caught. The attacks involve aerial chases with aerobatic twists and turns until their victim drops its food. At sea, smaller seabirds such as terns, kittiwakes, and auks act as the skuas’ main ‘hosts.’ Most skuas nest close to these species’ breeding colonies and match their own breeding time to that of their “victims” to steal from.
In North America, Arctic Jaegers are even called Parasitic Jaegers due to their habit of pursuing other seabirds and forcing them to drop their food. Jaeger/Jäger, the other term used for skua, is a German word meaning “hunter”, which again highlights their kleptoparasitic behaviour, accounting for almost the entirety of its diet during the winter migration season.

Long-distance Migration exploring the High Seas

Even if they are a Northern breeder, Arctic Jaegers have been spotted as far as the South Pole during their winter migration period. They are long-distance migratory seabirds and spend only around a third of the year at the breeding colony. British Trust for Ornithology (BTO) researchers have found that skuas from the same breeding population migrated to different wintering areas across the entire Atlantic Ocean – a pattern observed in other populations breeding globally. Furthermore, the mid-Atlantic is an important staging area for Arctic Jaegers during their northbound (spring) migration, where they feed up to get in good body condition before the breeding season. This mid-Atlantic area is a region of high marine productivity and, therefore, high food availability. Part of the region was recently designated as a Marine Protected Area (NACES MPA) due to its importance for numerous seabird species thanks to a study led by BirdLife.

Alarming declines

An alarming and rapid decline has been documented at Europe’s largest Arctic Jaeger colony in northern Norway, Slettnes. The decline in Arctic Jaegers along the coast of northern Norway is in line with decreasing numbers of Arctic Tern and Black-legged Kittiwake, on which Arctic Jaegers kleptoparasitise, with low fish stocks to blame. Predation is also causing low breeding success in the Slettnes’ (Norway) Arctic Jaeger colony due to the increase in Red Fox numbers in the area. The ongoing highly pathogenic avian influenza (HPAI) outbreak is increasing the pressure on the Jaeger’s population.

Skuas predating skuas

The RSPB has participated in collaborative studies to assess the relative impacts on breeding Arctic Jaegers of ‘bottom-up’ pressures, like food shortage, and ‘top-down’ pressures, such as predation. Over the past 30 years, Arctic Jaegers declined by 81% in some of its strongholds in Scotland. The decline is due to Great Skuas’ predation of chicks. Although Great Skuas are in the same family as the Arctic Jaeger, they are adding top-down pressures onto a species that is already facing significant bottom-up pressures due to lack of food.

Cover picture by Yves Adams