Classification Genome studies have shown that Frigatebirds, Gannets and Boobies, Cormorants and Shags, Anhingas and Darters form a monophyletic clade, meaning they descend from a common ancestor and they are the only progeny of this ancestor. For this reason, they have been moved from the Pelecaniforme to the newly individualized Suliforme order.
Fregatidae (Frigatebirds) are among the most aerial of all sea birds. Their best-known feeding habit involves piracy, in which they harry other sea birds until they disgorge their prey, after which the frigate birds catch the food in the air or pick it from the surface.
Sulidae (Gannets and Boobies) Although their feet have large webs, their legs are not streamlined, and they are not specialized for fast swimming. The feet are probably used underwater more for steering than for propulsion, and the birds depend mainly on the impetus of the dive (from more than 30 metres, about 100 feet) to enable them to approach their prey at high speed. When hunting in groups, Blue-footed Boobies tend to dive almost simultaneously. The simultaneous plunging of several birds may confuse the fish in a school and so increase each bird's chance of catching one. Red-footed boobies, and perhaps also other boobies, catch flying fish (family Exocoetidae) in the air as well as in the water.
Phalacrocoracidae (Cormorants and Shags) are adapted for underwater swimming. The cormorants pursue free-swimming or bottom-living fish, When feeding on schooling fish, cormorants often engage in mass fishing activities. Dives of most species usually last less than half a minute, although dives as long as one minute are not uncommon.
Anhingidae (Anhingas and Darters) do not pursue their prey but lie in wait underwater and then stab passing fish. Most of the fish that they eat are slow swimming and laterally flattened. Anhingas often stay underwater for as long as two minutes, and a dive of nearly seven minutes has been recorded in a captive bird.
pelecaniform (2012). Encyclopædia Britannica Ultimate Reference Suite Chicago: Encyclopædia Britannica. (The four families above used to be members of the "old"pelecaniform order and are described under that heading in the Encyclopedia Britannica.)