| Pelagic cormorant | |
|---|---|
 | |
| Nonbreeding adult (probablyP. p. resplendens) flying offMorro Rock (California, United States) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Suliformes |
| Family: | Phalacrocoracidae |
| Genus: | Urile |
| Species: | U. pelagicus |
| Binomial name | |
| Urile pelagicus (Pallas, 1811) | |
| Subspecies | |
2 subspecies (but see text) | |
| Synonyms | |
Phalacrocorax pelagicusPallas, 1811 | |
Thepelagic cormorant (Urile pelagicus), also known asBaird's cormorant orviolet-green cormorant, is a small member of thecormorantfamily Phalacrocoracidae. Analogous to other smallish cormorants, it is also called thepelagic shag occasionally. Thisseabird lives along the coasts of the northernPacific; during winter it can also be found in the openocean.[2] Pelagic cormorants have relatively short wings due to their need for economical movement underwater, and consequently have the highest flight costs of any bird.[3]
It was formerly classified in the genusPhalacrocorax, but a 2014 study supported reclassifying it and several other Pacific cormorant species into the genusUrile.[4] TheIOC followed this classification in 2021.[5]
This is a smallish cormorant which measures 25 to 35 in (64 to 89 cm) in length, with awingspan 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 metalliciridescence. In breeding plumage they grow two short crests (one on top of the head and one at thenape), whitethighs, and scattered whitefiloplumes on the head and neck. The long thinbill and the large feet withall-webbed toes are black throughout the year, while the patch of dark naked skin below the eye turns a vividmagenta in the breeding season.[2]
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.[2]
The widelysympatricred-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 inU. pelagicus, but extends to above the bill and above and behind the eye inU. urile; the latter species also has larger crests. Juveniles and nonbreeding adults of the twospecies 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 ofU. 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. Incourtship display, nest material is typically torn and moved about (whichU. urile might not do) and the males apparently do not bow their heads before the females asU. urile males do. Other North Pacific cormorants and shags are larger, with a thicker bill, and/or lack the white thighs in breeding plumage.[6]
The pelagic cormorant inhabits the shores and theneritic zone of theNorth Pacific. ItsNorth American range extends fromAlaska to theBaja California Peninsula inMexico. It furthermore is found on theAleutian and otherBering Strait islands, and from theRussian Far EastChukchi Peninsula viaSakhalin south toKamchatka, and ultimatelyKyūshū (though not the rest ofJapan). Thesubarcticpopulations aremigratory, while the birds fromtemperate andsubtropical regions only disperse locally after breeding, but even so Asian birds may reachChina orKorea.Vagrants have been recorded in theHawaiian Islands.[2]
On land, pelagic cormorants are rather clumsy and walk with the high-stepped waddling gait typical for allSulae exceptdarters; after landing they often scratch the ground, as is typical for cormorants. When they feel threatened, they will dart their bills at the intruder, and shake their heads and make a gargling noise. This bird forages by swimming to locateprey, then diving and going after it underwater, propelled by its feet and steering with the wings. It can dive as deep as 140 ft (43 m) to feed on or near theseafloor. Typical hunting grounds are shelteredinlets andbays; especially outside the breeding season they can also be seen fishing out at sea. They prefer to hunt in the vicinity ofkelp beds or among rocks. Typical prey are smallish, bottom-living non-schoolingfishes, such asAmmodytessand eels,sculpins (Cottidae),gunnels (Pholidae) andSebastes (rockfish). Apart from fish, smallcrustaceans – in particularshrimp – are also often eaten. It has been observed to joinmixed-species feeding flocks going after schools of youngPacific herrings (Clupea pallasii). Like all cormorants, due to their vestigialuropygial gland their plumage is notwaterproof. Thus, the birds return to a safe place after foraging topreen and dry their feathers, typically adopting a spread-winged posture.[7]
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The pelagic cormorant breeds onrocky shores and islands. They do not form largecolonies, but smaller groups may nest together. In some cases these birds alternate between two or three nesting sites in a region from one year to another. The nest is built at the cliff face, usually on ledges, less often in crevices or caves. The nest is built from stringyplants, such asgrasses orseaweed, and held together by the birds' ownguano. Once the birds have found a nest site they like, they tend to remain faithful to it for the rest of their lives. The nest is repaired and improved in each season if need be; it can thus grow up to 5 ft (1.5 m) deep.[2]
Males searching for a mate or bonding with their partner give an elaboratecourtship display, as is typical for Sulae. Like all cormorants, this includes stretching thegular sac with thehyoid bone and repeated "yawning"; as in many but not all cormorants, the pelagic cormorant's display furthermore includes arching the neck and hopping, lifting the folded wings and rapidly fluttering them to show the white thigh patches. During the yawning display, the head is thrown back and calls are given which differ between males and females; when the birds land, males and females give an identical call. Otherwise, the displays are given in silence.[8]
Theclutch is generally between two and fiveeggs, most often three or four, but clutches of up to seven eggs have been recorded.Incubation lasts for 3 weeks[9] to one month. At hatching, the young weigh somewhat more than an ounce (35 g) and are naked, but they soon growsooty-graydown feathers. In normal years, all young of a typical clutch may be raised successfully, but less than four rarelyfledge. On the other hand, during unfavorable phases of thePacific decadal oscillation, most pairs manage to raise only two young at most. They reachsexual maturity at two years of age, and a maximum age of almost eighteen years has been recorded in the wild.[10]
This numerous and widespread species is not considered threatened by theIUCN. The bulk of its population is found in the relatively inaccessible waters of the Bering Sea region; about 50,000 each breed in the Kuril Islands, the Bering Sea islands, and the U.S. state of Alaska and its offshore islands (including the Aleuts). About 25,000 breed down the Pacific coast of North America, some 60% of which are found in California. Local populations may be all but wiped out temporarily byoil spills, and on a larger scale competition withgillnet fisheries and drowning in such nets is putting a limit to its stocks.[2]
Theacanthocephalan parasiteAndracantha phalacrocoracis was described from this cormorant.[11]
The cormorantfamily Phalacrocoracidae has traditionally been included – like all otherbirds with fully webbed toes – in thePelecaniformes. But the namesakepelicans (Pelecanidae) are actually closer relatives ofstorks (Ciconiidae) than of cormorants. Hence, it has been proposed to separate the Phalacrocoracidae and relatives asorderPhalacrocoraciformes.[12] More recent evidence indicates that they and thedarters actually belong in the orderSuliformes, alongside theboobies andgannets.
Thisspecies was formerly placed in the catch-allgenusPhalacrocorax. Modern authors were previously reserved about uniting all cormorants in one "wastebin genus", but most revisions published had onphylogenetic merit. Though it was proposed to place the pelagic cormorant inStictocarbo for example, this is quite certainly wrong, as the present species is by no means closely related to thespotted shag (P. punctatus), thetype species ofStictocarbo. Similarly,Leucocarbo would refer to the group around theimperial shag (P. atriceps) complex, which occurs on the opposite end of the Earth fromP. pelagicus. The supposed "cliff shag"subfamily Leucocarboninae is entirelyparaphyletic 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 mostNorthern Hemisphere cormorants and shags, while Leucocarboninae would include mainlySouthern Hemispheretaxa.[13]
Another theory held that thegenus name for the pelagic cormorant, ifPhalacrocorax was to be split up, would beCompsohalieus. This name would apply to the group around itstype species (Brandt's cormorant,P. penicillatus). This is aNorth Pacificclade, which apart from Brandt's and the pelagic cormorant also includes thered-faced cormorant (P. urile) and probably also theextinctspectacled cormorant (P. perspicillatus). They all have black feet, and in breeding plumage grow whitefiloplumes on the head and/or neck, and usually also two head-crests and whitethigh patches like the present species does. They also share the back-thrown head during the "yawning" and the rapid wing-flutter incourtship display. Among theCompsohalieus group, the red-faced cormorant is thesister species ofP. 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 anapomorphy of these two species.[14] In 2014, a study was published supporting this treatment, albeit classifying the species in the genusUrile rather thanCompsohalieus. TheIUCN,BirdLife International, and theIOC have since followed this classification, legitimizing it.[5]
Its formerscientific name was the literalLatinizedAncient Greek equivalent of the common name:Phalacrocorax is an ancient term for cormorants; literally, it means "baldraven", fromfalakrós (φᾶλακρός, "bald") +kórax[15] (κόραξ, "raven").Pelagicus is – like theEnglishloanword "pelagic" – derived frompelágios (πελᾶγιος, "of the open seas").Compsohalieus, meanwhile, means "sleek fisher"; it derives fromkompsós (κομψός, "elegant" or "sleek") +(h)alieus'[16] (ἇλιεύς, "fisherman").[17]Urile is a term coined byBonaparte in 1855 as the species name for the red-faced cormorant.[4]
Twosubspecies are generally recognized. The difference between them is slight and generally agrees withBergmann's Rule:[2]
TheAmchitka cormorant orKenyon's shag (U. kenyoni) is a supposedspecies 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 atConstantine Harbor onAmchitka in theAleutian Islands. Thespecific namekenyoni honorsUSFWSbiologist Karl W. Kenyon, who collected thetype specimenUSNM 431164 on 22 February 1959. Some bones fromprehistoricmiddens on Amchitka were also attributed to thistaxon. As distinctive cormorants were never seen alive in recent years on Amchitka, it was conjectured by some that Kenyon's shag might have goneextinct in the 1960s–1970s (marine pollution andoverfishing would be possible reasons).[18]
However, a subsequent analysis of a larger number of comparison specimens of the pelagic cormorant – mainly from birds that fell victim to theExxon 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 originalcanonical 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 distinctsubspecies, the namekenyoni would apply. Verification of subspecies status would requireDNA sequence analyses however, since the differences inmorphology are not large and there is much variation between individuals.[19]
In 2003, during an USFWS survey three small pelagic cormorants whose bills appeared to be red were noted atKarab Cove onAgattu Island. It may be that these werekenyoni, but whether the bill color distinguishes the presumed subspecies or whether it is due to a simplemutation has not been determined. The large birds from thePrince William Sound region were formerly calledU. p. robustus, but are not considered distinct today. Since there appear to be at least two recognizable andallopatric size groups in the northern subspecies alone, more research is clearly necessary.[20]
