Pelagic Cormorant

Identificazione

This is a smallish cormorant which measures 25 to 35 in (64 to 89 cm) in length, with a wingspan of about 3.3 ft (1.0 m) and a weight of 52–86 oz (1,500–2,400 g) when fully grown. Adults in nonbreeding plumage are all-black with a metallic iridescence. In breeding plumage they grow two short crests (one on top of the head and one at the nape), white thighs, and scattered white filoplumes on the head and neck. The long thin bill and the large feet with all-webbed toes are black throughout the year, while the patch of dark naked skin below the eye turns a vivid magenta in the breeding season.<p>Males and females do not differ in appearance, though the latter is a bit smaller. Immature birds lack iridescence and are dark brown, grading into slightly lighter brown on the underside.<p>The widely sympatric red-faced cormorant (U. urile) looks very similar. Breeding adults are easily told apart by the amount of naked facial skin, which does not noticeably extend beyond the eye in U. pelagicus, but extends to above the bill and above and behind the eye in U. urile; the latter species also has larger crests. Juveniles and nonbreeding adults of the two species are often indistinguishable even to trained observers when in mixed flocks, or if they cannot be observed up close. In the former case, the large naked face "mask" and light bill of U. urile can be easily recognized, in the latter case its larger size (though male pelagic cormorants can be as large as female red-faced cormorants). Unlike the red-faced cormorant, the present species usually calls out before taking off, particularly during the breeding season. In courtship display, nest material is typically torn and moved about (which U. urile might not do) and the males apparently do not bow their heads before the females as U. urile males do. Other North Pacific cormorants and shags are larger, with a thicker bill, and/or lack the white thighs in breeding plumage.

Tassonomia

The cormorant family Phalacrocoracidae has traditionally been included – like all other birds with fully webbed toes – in the Pelecaniformes. But the namesake pelicans (Pelecanidae) are actually closer relatives of storks (Ciconiidae) than of cormorants. Hence, it has been proposed to separate the Phalacrocoracidae and relatives as order Phalacrocoraciformes. More recent evidence indicates that they and the darters actually belong in the order Suliformes, alongside the boobies and gannets.<p>This species was formerly placed in the catch-all genus Phalacrocorax. Modern authors were previously reserved about uniting all cormorants in one "wastebin genus", but most revisions published had on phylogenetic merit. Though it was proposed to place the pelagic cormorant in Stictocarbo for example, this is quite certainly wrong, as the present species is by no means closely related to the spotted shag (P. punctatus), the type species of Stictocarbo. Similarly, Leucocarbo would refer to the group around the imperial shag (P. atriceps) complex, which occurs on the opposite end of the Earth from P. pelagicus. The supposed "cliff shag" subfamily Leucocarboninae is entirely paraphyletic cannot be accepted as originally circumscribed. If subfamilies are to be accepted in the Phalacrocoracidae, the pelagic shag and its relatives would go in the Phalacrocoracinae like most Northern Hemisphere cormorants and shags, while Leucocarboninae would include mainly Southern Hemisphere taxa.<p>Another theory held that the genus name for the pelagic cormorant, if Phalacrocorax was to be split up, would be Compsohalieus. This name would apply to the group around its type species (Brandt's cormorant, P. penicillatus). This is a North Pacific clade, which apart from Brandt's and the pelagic cormorant also includes the red-faced cormorant (P. urile) and probably also the extinct spectacled cormorant (P. perspicillatus). They all have black feet, and in breeding plumage grow white filoplumes on the head and/or neck, and usually also two head-crests and white thigh patches like the present species does. They also share the back-thrown head during the "yawning" and the rapid wing-flutter in courtship display. Among the Compsohalieus group, the red-faced cormorant is the sister species of P. pelagicus. Apart from looking almost alike, these two species also "yawn" many times in a row instead of giving the display just once, twist their bodies before taking flight during courtship, and the male and female post-landing calls are identical. The point-and-gargle response to threats is also an apomorphy of these two species. In 2014, a study was published supporting this treatment, albeit classifying the species in the genus Urile rather than Compsohalieus. The IUCN, BirdLife International, and the IOC have since followed this classification, legitimizing it.<p>Its former scientific name was the literal Latinized Ancient Greek equivalent of the common name: Phalacrocorax is an ancient term for cormorants; literally, it means "bald raven", from falakrós (φᾶλακρός, "bald") + kórax (κόραξ, "raven"). Pelagicus is – like the English loanword "pelagic" – derived from pelágios (πελᾶγιος, "of the open seas"). Compsohalieus, meanwhile, means "sleek fisher"; it derives from kompsós (κομψός, "elegant" or "sleek") + (h)alieus' (ἇλιεύς, "fisherman"). Urile is a term coined by Bonaparte in 1855 as the species name for the red-faced cormorant.<p>Two subspecies are generally recognized. The difference between them is slight and generally agrees with Bergmann's Rule:<p>The Amchitka cormorant or Kenyon's shag (U. kenyoni) is a supposed species that was presumed to be closely related to the pelagic cormorant. It was described from the bones of three individuals snared in fishing nets in the late 1950s at Constantine Harbor on Amchitka in the Aleutian Islands. The specific name kenyoni honors USFWS biologist Karl W. Kenyon, who collected the type specimen USNM 431164 on 22 February 1959. Some bones from prehistoric middens on Amchitka were also attributed to this taxon. As distinctive cormorants were never seen alive in recent years on Amchitka, it was conjectured by some that Kenyon's shag might have gone extinct in the 1960s–1970s (marine pollution and overfishing would be possible reasons).<p>However, a subsequent analysis of a larger number of comparison specimens of the pelagic cormorant – mainly from birds that fell victim to the Exxon Valdez oil spill – determined that the bones were attributable to small females of the latter species, and that their apparent distinctness was due to the original canonical analysis being distorted by insufficient specimens. The researchers also found that contrary to what was generally assumed, pelagic cormorants from the Aleutians were generally small birds – as opposed to western Alaskan individuals, which are usually very large. If the Aleutian population were to be considered a distinct subspecies, the name kenyoni would apply. Verification of subspecies status would require DNA sequence analyses however, since the differences in morphology are not large and there is much variation between individuals.<p>In 2003, during an USFWS survey three small pelagic cormorants whose bills appeared to be red were noted at Karab Cove on Agattu Island. It may be that these were kenyoni, but whether the bill color distinguishes the presumed subspecies or whether it is due to a simple mutation has not been determined. The large birds from the Prince William Sound region were formerly called U. p. robustus, but are not considered distinct today. Since there appear to be at least two recognizable and allopatric size groups in the northern subspecies alone, more research is clearly necessary.

Nome scientifico

Urile pelagicus

Autorità

(Pallas, 1811)

Ordine

Suliformi

Famiglia

Phalacrocoracidae

Genere

Urile

Areale e habitat

The pelagic cormorant inhabits the shores and the neritic zone of the North Pacific. Its North American range extends from Alaska to the Baja California Peninsula in Mexico. It furthermore is found on the Aleutian and other Bering Strait islands, and from the Russian Far East Chukchi Peninsula via Sakhalin south to Kamchatka, and ultimately Kyūshū (though not the rest of Japan). The subarctic populations are migratory, while the birds from temperate and subtropical regions only disperse locally after breeding, but even so Asian birds may reach China or Korea. Vagrants have been recorded in the Hawaiian Islands.

Areale riproduttivo

PO : coastal Arctic to subtropical North Pacific Ocean, from ne Siberia to n Japan (w North Pacific) and Aleutian Is. to n Baja California (e North Pacific)

Areale non riproduttivo

s to Korean Pen. and ec China (w North Pacific); to w Baja California (nw Mexico; e North Pacific)

Migrazione

Migratori completi

Comportamento

Comportamento migratorio: Migratori completi.

Conservazione

Tendenza della popolazione: in diminuzione.

Tendenza della popolazione

in diminuzione