The Red-legged Cormorant, Phalacrocorax gaimardi, also known as the Red-legged Shag, Red-footed Cormorant, Red-footed Shag, Gaimard’s Cormorant and Grey Cormorant,^[1] is a resident of the coastline of South America. It is non-colonial unlike most seabirds. The Red-legged Cormorant has not been observed wing-spreading, which is characteristic of most cormorant species.^[2] It is considered near threatened under the IUCN Red List of Threatened Species.^[3]

Taxonomy

The Red-legged Cormorant is placed within the genus Phalacrocorax, but it has been debated that it should be placed within Notocarbo as phylogenetic studies suggest that it is most closely related to other southern-hemisphere shags, such as Spotted Shag.^[4] Its been suggested that the population of Red-legged Cormorants on the Atlantic coast are a separate subspecies. They are slightly smaller and have marginally paler plumage compared to the birds of the Pacific coast.^[2][1]

Description

The Red-legged Cormorant is a medium sized seabird, with a long neck, streamlined body, webbed feet and a long, thin hooked bill. Its body length is 71–76 centimetres (28–30 in), with an average wingspan of 91 cm (36 in).^[4] It weighs 1.3–1.5 kilograms (2.9–3.3 lb).^[2] There is no sexual dimorphism between the male and female Red-legged Cormorants.^[5]

The Red-legged Cormorant's appearance is unmistakable. Breeding adults have a smoky grey body, with a slightly paler underside. They have scattered areas of white filoplumes behind the eyes and down the neck. The wing coverts have a speckled, silvery grey appearance, followed by broad black wing tips. The tail is also black. The eyes are green, surrounded by sixteen tiny blue marks. The bill is yellow, shading to orange toward the base, the gular skin is a vibrant orange or red. The legs and feet are a striking coral red.

Non-breeding adults look similar to breeding adults. They lack the white filoplumes, the wing coverts appear less silvery, but more dark grey, and the bill and gular skin are duller in coloration.

Juvenile Red-legged Cormorants usually possess paler, brown plumage with a speckling of white around the throat. Juvenile plumage coloration can be highly variable between the Atlantic and Pacific coasts. Their eyes are grey and their bills and gular skin range from black to orange. The legs and feet can be a dull orange to a reddish black.^[2][1][6]

Distribution and Habitat

The Red-legged Cormorant is native to the coast of South America. On the Pacific coast it ranges from Macabi Island, Peru to Chiloe Island, Chile. There are small isolated populations on the Atlantic coast scattered across Santa Cruz, Argentina.^[2] It rarely occurs further south than the Strait of Magellan.^[7]

Red-legged Cormorants nest sparsely on steep rock faces, including coastal cliffs, rocky islets, and sea caverns. They become virtually undetectable against these rocky outcrops by their speckled grey plumage, with the exception of their colourful bills and feet.^[2] They forage within inshore bodies of water and in shallow offshore waters.^[8]

Behaviour

Feeding

Red-legged Cormorants are generally solitary foragers, but hunting in pairs or small flocks may occur.^[1] Most Red-legged Cormorants forage no further then 3 km away from their nest. They hunt in inshore waters, including estuaries, and in shallow offshore waters.^[8] They never enter exclusively fresh water.^[2] Many Red-legged Cormorants forage at low tide, presumably to minimize their travel time to and from the surface and to maximize time searching for food.^[8] They can dive 8–10 metres (26–33 ft) below the surface in pursuit of prey. Its diet mainly consists of fish, specifically including eels and anchovies, and planktonic crustaceans.^[1]

Reproduction

The Red-legged Cormorant is a non-colonial seabird, instead living in pairs or small groups. Courtship typically occurs in January and February. The males can engage in elaborate mating displays, which include darting and throwback postures. During darting, males chirp quietly while moving the head back and forth exposing the interior of the mouth.^[2] When the female advances, the male displays a throwback posture; outstretching the neck and pointing the bill towards the tail.^[1] The female may respond to the male's display by hopping and throat clicking. When the female selects a male, periods of allopreening ensue, followed by copulation. Red-legged Cormorant pairs are observed to be monogamous for at least one season.^[2]

Nests are constructed on steep cliffs and are usually isolated from other birds, but can form small colonies on rare occasions.^[7] They are composed of feathers, guano, seaweed, the cases of tube-dwelling worms and even garbage.^[9][5] They have been observed diving 8 to 10 meters collecting billfulls of various nesting materials.^[2] Egg laying takes place between October and January, with clutch sizes averaging three eggs.^[4] After hatching, the nestlings initially have no feathers, but are quickly covered in brownish down.^[2] As with all cormorants, nestlings are altricial, incubation period averages 30 days and the chick-rearing period is 60-70 days. ^{[2] [1]}

Vocalizations

The Red-legged Cormorants vocalizations are unlike most seabirds, they consist of high-pitched chirps and chirrups more like a songbird.^[1]

Predation

Due to the Red-legged Cormorants habit of nesting on cliffs with sheer rock faces and no ground approach, they are inaccessible to most predators.^[1] Their main predators is the Kelp Gull ^[10] along with humans, who consume adults, nestlings and eggs.^[1][5] The Red legged Cormorant’s threat display appears to be underdeveloped, consisting only of gaping and thrusting the bill towards the intruder. This could be due to its solitary life and lack of predators.^[1]

References

Further reading

• Carlos B. Zavalaga, Esteban Frere & Patricia Gandini (2002). "Status of the Red-Legged Cormorant in Peru: what factors affect distribution and numbers?". Waterbirds 25 (1): 8–15. JSTOR 1522265. 
• Esteban Frere, Flavio Quintana & Patricia Gandini (2002). "Diving behavior of the Red-Legged Cormorant in Southeastern Patagonia, Argentina". The Condor 104 (2). JSTOR 1370047. 
• Ana Millones, Esteban Frere & Patricia Gandini (2008). "Breeding habitat use by the Red-legged Cormorant (Phalacrocorax gaimardi) in Patagonia, Argentina". Waterbirds 31 (4): 656–660. doi:10.1675/1524-4695-31.4.656. 
• E. Frere, P. Gandini, J. Ruiz & Y. A. Vilina (2004). "Current status and breeding distribution of Red-legged Cormorant Phalacrocorax gaimardi along the Chilean coast". Bird Conservation International 14 (2): 113–121. doi:10.1017/S0959270904000139.