Phalacrocoracidae Cormorants and Shags
Version: 1.0 — Published March 4, 2020
Introduction
Cormorants and shags are foot-propelled divers that grasp their piscine prey with sharply hooked bills. Possessing poorly waterproofed plumage, they never wander far from shore, but they can be found on all but the most polar coasts, and inland on freshwater rivers and lakes. The plumage of Northern Hemisphere cormorants is mostly dark brown or black, but in the Southern Hemisphere there is a radiation of shags in boldly patterned grays and white and black. Some species are accented with bright red, yellow, or blue feet or facial skin. Their eyes, often of a beguiling blue or blue-green color, apparently focus very poorly under water, perhaps explaining why they often take such large fish.
Habitat
Most cormorant and shag species live along the sea coasts, breeding in large coastal colonies or on small islands just offshore; however, some species are primarily freshwater inhabitants.
Diet and Foraging
Cormorants and shags feed primarily on fish of a wide variety of species, but many also take a smaller number of crustaceans, mollusks, or cephalopods. Cormorants in Asia are sometimes adopted as household commensals, trained to dive for fish from a boat, fastened by a tether on a neck collar that is too tight to allow swallowing the fish they catch.
Breeding
Cormorants and shags are monogamous with biparental care. Though some species will nest in trees, they typically nest on the ground, often in a bowl-shaped nest made of seaweed and grass that is held together with mud and excrement, although some species merely construct a scrape on the ground. Cormorants and shags usually lay 2 to 4 eggs, although up to 7 can be laid. Both male and female assist in nest construction, incubation, and provisioning the chicks. Incubation begins after only the first or second egg is laid; thus chicks hatch asynchronously and develop an evident size hierarchy within the brood. Incubation takes 23 to 35 days, and the chicks fledge after 50 to 80 days in the nest. Post-fledging care can last up to 4 months.
Conservation Status
At least 14 cormorant species (41%) face conservation challenges, and populations have declined as a result of introduced mammalian predators, disturbance, changes to fisheries, and climate change (3 NT, 7 VU, 3 EN, 1 CR). One species has even gone extinct in the past 150 years: the Spectacled Cormorant Phalacrocorax perspicillatus, found on islands in the Bering Sea, was thought to be flightless (or nearly so) and went extinct shortly after being described.
Systematics History
Phalacrocoracidae traditionally has been placed in Pelecaniformes, but recent phylogenetic evidence shows that it is embedded within a group that also includes Anhingidae, Sulidae, and Fregatidae, which we treat here collectively as the order Suliformes. Within this group, Phalacrocoracidae is sister to Anhingidae, and these together are in turn sister to Sulidae, and these three together are sister to Fregatidae (Livezey & Zusi 2001, van Tuinen et al. 2001, Ericson et al. 2006a, Hackett et al. 2008).
Conservation Status
Least Concern |
50%
|
---|---|
Near Threatened |
5%
|
Vulnerable |
17.5%
|
Endangered |
7.5%
|
Critically Endangered |
2.5%
|
Extinct in the Wild |
0%
|
Extinct |
2.5%
|
Not Evaluated |
0%
|
Data Deficient |
0%
|
Unknown |
15%
|
Data provided by IUCN (2023) Red List. More information