Flightless cormorant
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| Elizabeth Bay, Isabela Island, Galapagos. | |
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P. harrisi
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| Phalacrocorax harrisi (Rothschild, 1898)
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The flightless cormorant (Phalacrocorax harrisi), also known as the Galapagos cormorant, is a cormorant native to the Galapagos Islands, and an example of the highly unusual fauna there. It is unique in that it is the only cormorant that has lost the ability to fly. Once it was placed in its own genus, Nannopterum or Compsohalieus, although current taxonomy places it in the genus with most of the other cormorants, Phalacrocorax.
Contents
Description
Like all cormorants, this bird has webbed feet and powerful legs that propel it through ocean waters as it seeks its prey of fish, eels, small octopuses, and other small creatures. They feed near the sea floor and no more than 100 m offshore.
The flightless cormorant is the largest extant member of its family, 89–100 cm (35–40 in) in length and weighing 2.5–5.0 kg (5.5-11 lbs), and its wings are about one-third the size that would be required for a bird of its proportions to fly. The keel on the breastbone, where birds attach the large muscles needed for flight, is also greatly reduced.
The flightless cormorants look slightly like a duck, except for their short, stubby wings. The upperparts are blackish and the underparts are brown. The long beak is hooked at the tip and the eye is turquoise. Like all members of the cormorant family, all four toes are joined by webbed skin. Males and females are similar in appearance, although males tend to be larger. Juveniles are generally similar to adults but differ in that they are glossy black in colour with a dark eye. Adults produce low growling vocalizations.
Like other cormorants, this bird's feathers are not waterproof, and they spend time after each dive drying their small wings in the sunlight. Their flight and contour feathers are much like those of other cormorants, but their body feathers are much thicker, softer, denser, and more hair-like. They produce very little oil from their preen gland; it is the air trapped in their dense plumage that prevents them from becoming waterlogged.
Distribution and habitat
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This unique cormorant is endemic to the Galapagos Islands, Ecuador, where it has a very restricted range. It is found on just two islands; Fernandina, where it is found mainly on the east coast, as well as on the northern and western coasts of Isabela. The population has undergone severe fluctuations; the 1983 El Niño event resulted in a 50% reduction of the population to just 400 individuals. The population recovered quickly, however, and was estimated to number 900 individuals in 1999.
This species inhabits the rocky shores of the volcanic islands on which it occurs. It forages in shallow coastal waters, including bays and straits and rarely ventures further than one kilometer from the breeding areas.
Behavior
Breeding
Nesting tends to take place during the coldest months (July–October), when marine food is at its most abundant and the risk of heat stress to the chicks is decreased. At this time, breeding colonies consisting of around 12 pairs form. The courtship behavior of this species begins in the sea; the male and female swim around each other with their necks bent into a snake-like position. They then move onto land. The bulky seaweed nest, located just above the high-tide mark, is augmented with "gifts" including pieces of flotsam such as rope and bottle caps, which are presented to the female by the male.
The female generally lays three whitish eggs per clutch, though usually only one chick survives. Both male and female share in incubation. Once the eggs have hatched, both parents continue to share responsibilities of feeding and brooding (protecting the chicks from exposure to heat and cold), but once the chicks are old enough to be independent, and if food supplies are plentiful, the female will leave the male to carry out further parenting, and she will leave to find a new mate. Females can breed three times in a single year. Thus, although their population size is small, flightless cormorants can recover fairly quickly from environmental disasters.
Conservation
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These cormorants evolved on an island habitat that was free of predators. Having no enemies, and taking its food primarily through diving along the food-rich shorelines, the bird eventually became flightless. However, since their discovery by man, the islands have not remained free of predators: cats, dogs, and pigs have been introduced to the islands over the years. In addition, these birds have no fear of humans and can easily be approached and picked up.
In the past, introduced feral dogs were a great threat to the species on Isabela, but they have since been eradicated from the island. Future introduction of rats or cats to Fernandina is a huge potential threat to the species. Fishing with nets poses a current threat to the species; this not only reduces the availability of the cormorant's food, but also often results in birds becoming caught in the nets and killed.
The fact that this uniquely adapted bird is found in such a small range and in such small numbers greatly increases its vulnerability to chance events such as environmental disasters (especially an oil spill), extreme climatic events and the introduction of diseases or predators. Unfortunately, marine perturbations such as those caused by El Niño events are becoming increasingly extreme. Still, its ability to breed quickly can allow it to recover from disasters as long as the population remains above the critical level.
Because of these factors, the flightless cormorant is one of the world's rarest birds. A survey carried out by the Charles Darwin Research Station in 2004 indicated that the species has a population of about 1,500 individuals. In 2009, BirdLife International set the number of individuals of the flightless cormorant at only 900 individuals, although a more recent estimate in 2011 was 1679 individuals.[2] It was formerly classified as Endangered by the IUCN, but recent research shows that it is not as rare as previously believed and that its population has stabilized. Consequently, it was downlisted to Vulnerable in 2011.[3]
All populations of this species are found within the Galapagos National Park and Marine Reserve; furthermore, the archipelago was designated as a World Heritage Site in 1978.[4] The Charles Darwin Research Station has monitored the species regularly to keep track of fluctuations in numbers over time. The species is considered vulnerable, and conservation proposals include the continuation of annual monitoring programs, the reduction of disturbance by humans, and the prevention of fishing with nets in the bird's foraging range.
References
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- ↑ BLI (2011)
- ↑ BLI (2011)
- ↑ http://whc.unesco.org/en/list/1
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- RIT.edu - personal observations of the flightless cormorant by Dr. Robert Rothman.
- IUCN Red List of Threatened Species 2003 (March 2004)
- BirdLife International 2003 BirdLife's online World Bird Database: the site for bird conservation Version 2.0. Cambridge, UK: BirdLife International (March 2004)
- UNEP-WCMC/ WWF Species Fact Sheet – flightless cormorant (March 2004)
- Galapagos Conservation Trust – flightless cormorant (March 2004)
- Livezey, B.C. (1992) Flightlessness in the Galapagos cormorant (Compsohalieus [Nannopterum] harrisi): heterochrony, gigantism and specialisation. Zoological Journal of the Linnean Society, 105: 155.
- Allaby, M. (1991) The Concise Oxford Dictionary of Zoology. Oxford University Press, Oxford.
- The flightless cormorant – Prof. Robert H. Rothman (March 2004)
External links
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