Pelagic cormorant

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Pelagic cormorant
Nonbreeding adult (probably P. p. resplendens) flying off Morro Rock (California, United States)

Least Concern  (IUCN 3.1)[1]
Scientific classification Edit this 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 pelagicus Pallas, 1811
Leucocarbo pelagicus (Pallas, 1811)
Phalacrocorax kenyoni (Siegel-Causey, 1991)
Stictocarbo kenyoni Siegel-Causey, 1991
Stictocarbo pelagicus (Pallas, 1811)

The pelagic cormorant (Urile pelagicus), also known as Baird's cormorant or violet-green cormorant, is a small member of the

Pacific; during winter it can also be found in the open ocean.[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 genus Phalacrocorax, but a 2014 study supported reclassifying it and several other Pacific cormorant species into the genus Urile.[4] The IOC followed this classification in 2021.[5]

Description

Nonbreeding adult U. p. resplendens on Morro Rock (California, United States)

This is a smallish cormorant which measures 25 to 35 in (64 to 89 cm) in length, with a

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.[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 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.[6]

Range

The pelagic cormorant inhabits the shores and the

Vagrants have been recorded in the Hawaiian Islands.[2]

Ecology and biology

Diet

preening
after fishing. Note spread-winged posture of bird in center.

On land, pelagic cormorants are rather clumsy and walk with the high-stepped waddling gait typical for all

preen and dry their feathers, typically adopting a spread-winged posture.[7]

Breeding

Adult on a nest in San Luis Obispo, California, United States
A parent with approximately one-month-old chicks on a nest

The pelagic cormorant breeds on

grasses or seaweed, and held together by the birds' own guano. 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 elaborate

gular sac with the hyoid 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]

The

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 grow sooty-gray down feathers. In normal years, all young of a typical clutch may be raised successfully, but less than four rarely fledge. On the other hand, during unfavorable phases of the Pacific decadal oscillation, most pairs manage to raise only two young at most. They reach sexual maturity at two years of age, and a maximum age of almost eighteen years has been recorded in the wild.[10]

Status

This numerous and widespread species is not considered threatened by the

gillnet fisheries and drowning in such nets is putting a limit to its stocks.[2]

The

Andracantha phalacrocoracis was described from this cormorant.[11]

Taxonomy and systematics

The cormorant

Phalacrocoraciformes.[12] More recent evidence indicates that they and the darters actually belong in the order Suliformes, alongside the boobies and gannets
.

sister species

This

taxa.[13]

Another theory held that the

apomorphy of these two species.[14] 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.[5]

Its former

pelagic" – derived from pelágios (πελᾶγιος, "of the open seas"). Compsohalieus, meanwhile, means "sleek fisher"; it derives from kompsós (κομψός, "elegant" or "sleek") + (h)alieus'[16] (ἇλιεύς, "fisherman").[17] Urile is a term coined by Bonaparte in 1855 as the species name for the red-faced cormorant.[4]

Subspecies

Two

Bergmann's Rule:[2]

The Amchitka cormorant or Kenyon's shag (U. kenyoni) is a supposed

extinct in the 1960s–1970s (marine pollution and overfishing 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 the

DNA sequence analyses however, since the differences in morphology 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 at

allopatric size groups in the northern subspecies alone, more research is clearly necessary.[20]

Footnotes

  1. doi:10.2305/IUCN.UK.2019-3.RLTS.T22728950A155630943.en
    . Retrieved 12 November 2021.
  2. ^ a b c d e f g Orta (1992a)
  3. PMID 23690614
    .
  4. ^
    PMID 24994028
    .
  5. ^ a b "Taxonomic Updates – IOC World Bird List". Retrieved 2021-07-28.
  6. ^ Siegel-Causey (1991), Orta (1992a), Kennedy et al. (1996)
  7. ^ Orta (1992a,b), Kennedy et al. (1996)
  8. ^ Kennedy et al. (1996)
  9. ^ "PELAGIC CORMORANT Phalacrocorax pelagicus" (PDF). U.S Fish & Wildlife Service.
  10. ^ Orta (1992a), AnAge [2009]
  11. ^ Monteiro et al. (2003)
  12. ^ Christidis & Boles (2008)
  13. ^ Orta (1992a), Siegel-Causey (1988), Kennedy et al. (2000)
  14. ^ Orta (1992a,b), Kennedy et al. (1996, 2000)
  15. Modern Greek
    : koráki (κοράκι)
  16. ^ Modern Greek: aliéas (αλιέας)
  17. ^ Woodhouse (1910)
  18. ^ Siegel-Causey (1991), Siegel-Causey et al. (1991), Fuller (2000): p.382
  19. ^ Rohwer et al. (2000)
  20. ^ Hobson (1997), Rohwer et al. (2000), Byrd & Williams (2004)

References

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