The Great Cormorant - extinct and back again in Sweden

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The Great Cormorant - extinct and back again in Sweden

Discover Sörmland Blog
Published by Stefanie Schlosser in Nature · 17 February 2022
Tags: cormorantnature
The great cormorant (Phalacrocorax carbo) is a member of the cormorant family of seabirds and can be found all across the world, except in Antarctica and South America.

In Sweden, the cormorant’s habitat ranges from Southern and Middle Sweden until the coast of Norrland. Phalacrocorax carbo is breeding both in the archipelago and at some inland lakes, like Mälaren in Stockholms län. However, mostly it is found along the Baltic Sea coast.

Most of the Swedish cormorants spend winter time in Southern Europe and a couple stays together for one season only. Interestingly, cormorants show different breeding behavior in different regions. Those in the Kalmar Strait for example breed only in the crowns of pine trees while those along the bay Bråviken breed directly on the rocky cliffs.
Taxonomists classify different subspecies. In Sörmland the great cormorant Phalacrocorax carbo appears in two subspecies (P. carbo carbo and P. carbo sinensis) which are very hard to distinguish and therefore mostly seen as one.
During the 19th century, great cormorants were only breeding in Southern Sweden. Humans saw them as competitors for fish and pursued them until their extinction. About 40 years later, some colonies established in the southern Kalmar Strait and from there the cormorant spread across the country again.

The population has increased from 340 pairs in 1975 to 45.000 pairs in 2006, from where on it stagnated or decreased slightly, depending on the area. 2012 Sörmland counted 2.320 pairs in 11 colonies. Compared to the peak in 2008 the population has slightly decreased here.

In the complexity of ecosystems, it’s hardly possible to identify a single root cause for certain developments. Many environmental factors influence both growth and reproduction rate of any species. The overfertilization of the Baltic Sea for example leads to an abundant food supply for cormorants and therefore enhances the population’s growth, while the white-tailed sea-eagles found both eggs and young cormorant birds to be a great food source as well. Environmental toxins and pollution through plastic presents another thread to the great cormorant. At present moment Phalacrocorax carbo occurs numerous throughout a wide range of habitats and the conservation status given by the IUCN is “least concern”.

Fig.1: Cormorant diving in Tamaríu, Spain (Maria Pichlmaier, Stollis Divebase)

While the great cormorant’s movements on land are a bit clunky, it is a very elegant swimmer, diver and fisher. Its feathering absorbs water and thereby minimizes both buoyancy and resistance when moving under water. The feathers, however, need to be dried after each dive. It is therefore we often can see cormorants sitting on the rocks with their wings widespread.

Fig.2: Cormorant (Ken Billington; CC-BY-SA 3.0)

Stunning fact: Historically, great cormorants were used for fishing! With a rope around their neck, they were prevented from swallowing the fish, which instead was taken by the fisherman. In Asia, this practice is still used – nowadays even for tourist attraction.

Fig.3: Cormorant fishing on Eir lake near Dali, Yunan, China (Frédéric Lemaréchal; CC-BY-1.0)

Have you already seen the great cormorants sitting by the water, with their wings spread wide? Please share your experiences in the comments below.

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17 Feb 2022
genial 😍👌🏻
© Stefanie Schlosser 2023
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