Animal Diversity Web

Pelecaniformes comprises six families (Phaethontidae (tropicbirds), Sulidae (boobies and gannets), Phalacrocoracidae (cormorants and shags), Anhingidae (anhingas), Pelecanidae (pelicans) and Fregatidae (frigatebirds)), six genera, and 67 species.

Pelecaniform birds are distributed worldwide, primarily in coastal and marine zones.

Pelecaniform birds inhabit marine and inland waters. Habitat varies from pelagic to coastal to inland freshwater environments.

Incubation ranges from 25-55 days. Young are altricial and all chicks, except tropicbirds, are born without natal down. Fledging age is highly variable, ranging from 65-210 days. Post-fledging care is pronounced and may last for as long as 18 months in some species. Age at first breeding varies with species and ranges from two to perhaps eleven years.

Pelecaniform birds are medium to large aquatic birds with totipalmate feet (all four toes joined by web). Most have distensible gular sac located between the branches of the lower mandible. In tropicbirds the small gular region is feathered, in pelicans the bare sac is pendulous, and in frigatebirds the large, bare, red gular sac is inflatable. Only tropicbirds have exposed external nares. All pelecaniform birds' skulls lack supraorbital groove for a nasal gland and dorsal vertebrae are opisthocoelous. Plumage ranges from mostly black with some white to mostly white with some black. Feet and bare regions of face and gular sac may become brightly colored during breeding. Most have desmognathous palate, except tropicbirds, which have schizognathous palate. All except frigatebirds lack brood patches.

Many pelecaniforms breed in mixed colonies with other pelecaniforms, gulls, terns, or penguins.

Pelecaniform birds feed primarily on fish and squid. They may also prey on mollusks, crustaceans, amphibians, reptiles, and invertebrates.

Predators of pelecaniform birds include humans, birds, rats, cats, dogs, and reptiles.

Most pelecaniform birds are considered seasonally monogamous. Nest-sites and mates may change from year to year, except perhaps for sulids. Mating displays and pair formation behaviors are elaborate and complex. Generally males display to attract females. Females defend the nest-site and construct the nest from materials collected by the male. Copulations generally occur at the nest or display site.

Breeding may be annual or biennial, seasonal or year round. Pelecaniform birds nest in colonies, sometimes consisting of thousands of pairs. Nest sites are variable, located on the ground, in trees or shrubs, or on cliff ledges. Nests may be insubstantial scrapes or constructions of twigs and other materials. Clutch size varies with species and ranges from one to six eggs. Egg color ranges from white to pale green-blue to red-brown.

In pelecaniform birds both sexes take approximately equal stints incubating eggs. All species except the frigatids lack brood patches and use foot webbing to transfer heat to eggs. Duration of incubation varies considerably from 24 -57 days. Both parents brood and feed chicks regurgitated food. Many species have post-fledging care where parents continue to feed chicks, in some species post-fledging care is prolonged and may last for as long as 18 months.

Some pelecaniforms are migratory whereas others are mostly sedentary with wide dispersal of young. All pelecaniforms are aquatic birds and associated with large bodies of water. Foraging techniques vary from hunting singly to foraging cooperatively in large groups, from plunge diving to surface diving, from underwater stalking ambushes to aerial and underwater pursuit diving. Species with large gular sacs use them in conjunction with foraging, mating displays and thermoregulation.

Most pelecaniforms are gregarious, gathering in colonies for breeding and roosting in large groups.

Pelecaniforms are notably noisy when in large groups. Vocalizations are variable with species, and range from the sharp piercing whistle of the tropicbirds to the guttural grunting of cormorants.

Humans exploit pelecaniform birds extensively. The eggs, chicks, and/or adults of many species are collected for consumption, purported medicinal purposes, or for goods and clothing. Humans collect and sell pelecaniform guano as fertilizer. Some species are trained and used by humans in conjunction with fishing.

Twenty-two pelecaniform species are included in the IUCN Red List of Threatened Species.

One species, Pallas's Cormorant (Phalacrocorax perspicillatus), is listed as 'Extinct'; two are listed as 'Critically Endangered' (Andrew's Frigatebird (Fregata andrewsi) and Abbott's Booby (Papasula abbotti)); and two species are listed as 'Endangered', (Flightless Cormorant (Phalacrocorax harrisi) and Chatham Island Shag (P. onslowi)). Of the remaining species, eleven are listed as 'Vulnerable' and six are 'Lower Risk'. Major threats include habitat destruction, introduced predators, pesticide poisoning and oil spills.

The evolutionary relationships of pelecaniform birds remain unclear and the monophyly of Pelecaniformes is strongly debated. Traditionally, Pelecaniformes (or Steganopodes) is a group comprising six families including:(Phaethontidae (tropicbirds), Sulidae (boobies and gannets), Phalacrocoracidae (cormorants and shags), Anhingidae (anhingas), Pelecanidae (pelicans) and Fregatidae (frigatebirds). Analyses of morphological and ethological evidence suggest that phaethontids are relatively primitive whereas frigatids are relatively most derived of the group. In contrast, fossil evidence appears to support the hypothesis that phaethontids and frigatids fall basal relative to the rest of the group. Some morphological evidence supports the monophyly of Pelecaniformes and its sister group relationships with procellariids (albatrosses, petrels, shearwaters) and ciconiids (storks, herons, ibises, spoonbills). Some molecular, ethological, and morphological evidence refutes the monophyly of Pelecaniformes. One hierarchy based on DNA hybridization places phaethontids sister to a group comprising sulids, anhingids, and phalacrocoracids; pelecanids as sister to a Shoebill Stork (Balaeniceps); and frigatids as sister to spheniscids (penguins) and included in a group (Procellarioidea) along with gaviids (loons) and procellariids (petrels, shearwaters, albatrosses).

The oldest pelecaniform fossils include a phaethontid (Prophaethon) from England dating from the early Eocene and a fregatid (Limnofregata) from Wyoming also dating to the Eocene. Phalacrocoracid fossils extend back to the Eocene-Oligocene boundary.

Sulid (Sula ronzoni) and pelecanid (Pelecanus gracilis) fossils from France date from the early Oligocene and lower Miocene respectively. Old and New world fossil anhingids date from the early (Anhinga subvolans) and the late (A. pannonica, A. grandis) Miocene.

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Feduccia, A. 1999. The Origin and Evolution of Birds, 2nd edition. Yale University Press New Haven.

Johnsgard, P. A. 1993. Cormorants, Darters, and Pelicans of the World. Smithsonian Institution Press Washington.

Sibley, C. G. & J. E. Ahlquist. 1990. Phylogeny and Classification of Birds, A Study in Molecular Evolution. Yale Univ. Press.

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Van Tets, G. F. 1976. Australasia and the origin of shags and cormorants, Phalacrocoracidae. Pp. 121-24 in: Proc. 16th Inter. Ornith. Congr. Canberra, Australia, 1974.

Contributors

Laura Howard (author), Animal Diversity Web.