Great Cormorant
The great cormorant (Phalacrocorax carbo) is a large, powerful water bird known for its exceptional diving abilities and widespread global presence. First described by Carl Linnaeus in 1758, this species is a member of the order Suliformes and the family Phalacrocoracidae. Its name reflects its appearance: the genus Phalacrocorax is derived from the Ancient Greek words for "bald" and "raven," while the specific epithet carbo is Latin for "charcoal," referencing its deep black plumage.
From the rocky coasts of the North Atlantic to the inland waterways of Asia and Africa, the great cormorant has adapted to a variety of aquatic environments, making it one of the most successful members of its genus.
Key Facts
- Conservation Status: Least Concern (IUCN 3.1).
- Size: Length varies from 70 to 102 cm; wingspan ranges from 121 to 160 cm.
- Weight: Ranges from 1.5 kg to 5.3 kg, with males typically larger than females.
- Diet: Primarily fish, captured via foot-propelled diving.
- Nesting: Colonial breeders that use sticks to build nests in trees, cliffs, or on rocky islands.
- Special Ability: Evolved hearing optimized for underwater detection of prey.
Taxonomy and Subspecies
The great cormorant is categorized into several subspecies, often distinguished by their geographic distribution and subtle physical differences. While identification can be challenging due to hybridization, experts often look at the shape of the gular skin patch (the skin of the throat) to differentiate between them.
| Scientific Name | Common Name | Primary Distribution | Distinguishing Features |
|---|---|---|---|
| P. c. carbo | Atlantic cormorant | North Atlantic / Europe | Nominate race; acute angle gular patch |
| P. c. sinensis | Continental cormorant | Europe / Asia | Obtuse angle gular patch |
| P. c. hanedae | Japanese great cormorant | Japan (Hokkaido to Kyushu) | Often found inland; ecologically separate from P. capillatus |
| P. c. maroccanus | Moroccan cormorant | Northwest Africa | White neck and upper breast |
| P. c. lucidus | White-breasted cormorant | Sub-Saharan Africa | White neck and breast |
| P. c. novaehollandiae | Black cormorant / Black shag | Australia and New Zealand | Known as "kawau" in Māori |
Physical Description and Identification
The great cormorant is characterized by its heavy build and dark plumage. In European waters, it is larger and bulkier than the European shag, possessing a thicker bill and lacking a crest. Its plumage often exhibits a purple tinge, whereas the shag's is more green. In North America, it is distinguished from the double-crested cormorant by its larger size, the presence of white thigh patches during breeding, and having 14 tail feathers instead of 12.
Behavior and Ecology
Feeding and Diving
The great cormorant is a specialist in foot-propelled diving. It captures prey in its beak, diving to depths of up to 9.5 meters (31 ft) for durations of 1 to 3 minutes. Research indicates that approximately 60% of these dives target the benthic zone (the lowest level of a body of water), while 10% target the pelagic zone (the open ocean/water column).
Interestingly, their hearing has evolved for underwater use to help detect fish, though this adaptation results in lower hearing sensitivity when the bird is in the air.
Breeding and Nesting
These birds are colonial breeders, often returning to the same nest site year after year. They construct nests from sticks in various locations, including cliff ledges, trees, and predator-free rocky islands. A typical clutch consists of three to five pale blue or green eggs, which are incubated for 28 to 31 days.
Human Relationships and Conservation
The relationship between humans and the great cormorant is complex. Because they are efficient fishers, they are often viewed as competitors by commercial and recreational fishermen. This led to historical hunting that nearly drove the species to extinction in some areas. However, conservation efforts have seen populations rebound; there are currently about 1.2 million birds in Europe.
In some cultures, the bird holds a different status. In North Norway, cormorants are traditionally seen as semi-sacred, and legends suggest that those lost at sea spend eternity on the mythical island of Utrøst, visiting home in the form of cormorants. In other regions, such as China, cormorants have been traditionally trained for fishing.
Health Threats
As colonial breeders, great cormorants are highly susceptible to highly pathogenic avian influenza (HPAI). Significant outbreaks have occurred in the Baltic Sea, where over 1,700 birds died between 2021 and 2022.
Frequently Asked Questions
How can you tell a great cormorant apart from a shag?
The great cormorant is generally larger and heavier, has a thicker bill, lacks a crest, and has plumage with a purple tinge rather than green. Additionally, it has 14 tail feathers, while the European shag has 12.
What is the diet of the great cormorant?
The great cormorant primarily eats fish, which it captures by diving. It utilizes both the benthic zone (bottom) and pelagic zone (open water) to find prey.
Are great cormorants protected?
Their status is "Least Concern" globally. However, legal protections vary by region. For example, in the UK, it is illegal to kill a cormorant without a specific license, although some licenses are issued to manage predation in fisheries.
Why do they have specialized hearing?
Their hearing has evolved to be more effective underwater, which likely aids them in detecting the movement and location of fish while diving.